JOVE MEMORANDUM

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TO:

FROM:

DATE:

SUBJECT:

JOVE Faculty Research Associates

Maury Estes

JOVE Program Office

May 16, 1997

JOVE ,amnualProgressReport

Enclosed you will find an Annual Progress Report form and a copy of the JOVE

Performance Expectations. The information you provide through this report is invaluable

to us in providing statistics/metrics for NASA regarding the program and will be used to

evaluate your performance against the JOVE Performance Expectations. A Feedback

Letter regarding your performance will be sent to you in the fall.

,M1 schools with grants which expire in ,May of 1997 will receive an additional form

requesting information that will be necessary for grant close-out. This form should be

completed only if you do not anticipate an extension of your grant or a JOVE

Augmentation Grant.

This year's deadline for reports is June 30. Please mail 3 copies of your completed report

(including attachments) to USKA/JOVE, 4950 Corporate Drive, Suite 100, Huntsville, AL

35805. To obtain an electronic copy of the ProgresI Report in Microsoft Excel

format contact Mona Miller via mona@apace.hav.usra.edu.

We greatly appreciate the hard work that goes into preparing this report and look forward

to learning more about your project. Please notify me or Debbie Hurst at (205) 895-0582

if you have questions.
JOVE FINAL TECHNICAL REPORT*

Note: Please print or tl_pe.

Dr. Benjamin K. l_lphrus

Naun6

b. ma1phr@morehead- st. edu

E-Mail Address

Date: 6/27/97

Morehead State University

Institution

NAG8-1119

Grant Number

Io Comprehensive summary of research conducted under this

NASA/JOVE grant. (Attach adcZltional page (s) if neceimary. )

See attached document.

II. Please list all subject inventions/patents as a result of

your Grant or provide a statement that there were none.

No patents or inventions resulted from this project.

Signature _ / f Date -- /

*Complete this form only if you do not anticipate continuing your research on

a No-Cost Extension or on a JOVE Augmentation Grant (JAG}.
I. Comprehensive summary of research conducted under this NASA/JOVE grant.

The goal of this project has been to search for genuinely young irregular galaxies that have formed

during gravitational encounters. The research has specifically involved high spatial resolution HI

observations made using the VLA of NGC 5291, an interacting system consisting of a massive

lenticular galaxy, companion galaxy and gaseous extensions. During the internship, data that had

been collected by the mentor was calibrated, edited, reduced, and images of the HI distribution and

kinematics produced. The 1995 academic year was devoted to further imaging and to the analysis

of these data. Results indicated that dwarf irregular galaxies had indeed formed from material

tidally removed from the interacting pair. Our observations of NGC 5291 show that some of the

associations of HI and HII would be considered dwarf irregular galaxies, if they were isolated

objects. Initial results were reported at the January meeting of the AAS and via a press release

requested by the AAS. The 1996 academic year was devoted to further analysis of the data in an

attempt to prove that the young galaxy is bound against its own internal kinetic energy and lies

outside of the tidal radius of the host galaxy. An analysis method was developed that can be

applied to observations of additional systems. This initial study proved the viability of the

•observation and analysis procedures in searching for genuinely young dwarf irregular galaxies

formed in interaction fields. A scientific paper describing these observational and analysis

procedures was prepared, submitted, and accepted for publication in the Astronomical Journal.

We have begun to define the role that collisions play in the building of irregular galaxies. New

questions, however, are indicated by the research. What can be said about the long term stability of

these potential dwarf systems? How do they evolve during the course of the interaction; do they

tend to fall back into the galaxy or remain free as dwarf satellites, possibly in orbit? The next

phase of the research will be devoted to developing proposals to observe other systems in attempt

to prove that the phenomenon is not unique indicating that many if not all dwarf irregular galaxies

have formed from material removed from major galaxies during mergers and gravitational

encounters.

Two observing proposals were developed and submitted to the VIA. A multi-institutional research

proposal involving was developed and submitted to NSF in which 21 cm observations will be

combined with optical and infrared (IR) observations (provided by our collaborators at the Instituto

de Astrofisica de Canarias (IAC)) and numerical simulations in a comprehensive program. This

research could ultimately contribute to our understanding of galactic evolution resulting

from gravitational encounters.

JOVE ANNUAL P_SS REPORT: ACADEMIC YEAR 1996-97"

Wot_: PleaJe print o: tTpe.

Dr. Ben Malphrus

Nm

E-Mail Address: b.malphr@ morehead-st.edu

Date :

Morehead State University

6/27197

Zrult_. _:u_.ion

Grant Numbe_:

,_IAG8-1119

Z. RESE,_

Brief dmseri_tion of rese_re.h =esm.].'cJ to date on _our pZ'O3eCt::

The goal of this project has been to search for genuinely young irregular galaxies that have formed during

gravitational encounters. The research has specifically involved high spatial resolution HI observations made using

the VLA of NGC 5291, an interacting system consisting of a massive lenticuiar galaxy, companion galaxy and

gaseous extensions. During the internship, data that had been collected by the mentor was calibrated, edited, reduced.

and images of the HI distnbuuon and kinematics produced. Results indicate that a dwarf irmguJar galaxy had indeed

formed from mamnal tidally removed from the mteracung parr. Imual results were reported at the January meeung

of the AAS and via a press release requested by the AAS. The 1996 academic year was devoted to further analysis

(i.e. gravitational stability) of the system. An analysis method was developed that can be applied to observations of

addiuonal systems. In addition, a scientific paper was prepared, subnntted, and accepted for publication in the

Astronomical Journal. The next phase of the research will be devoted to developing proposals to observe other

systems in attempt to prove that the phenomenon is not unique indicating that many if not all dwarf irregular

g_ies have formed from mamnal removed from major galaxies during mergers and gravitational encounter. An

exW,nsive multi-wavelength, multi-institulon project has been initiatied. Two observing proposals were developed

and submitted to the VLA. A multi-institutional research proposal was developed and submitted to NSF.

]?lem i¢le_P.i£_ the clapt =etm, if a.zl_e nlmd _ _ Z_lMtlt.TC=h.

NASA Exlragalactic Database (NED), Astrophysical Journal Abstracts, SpaceLink, SkyView, NRAO WWW pages.

Interaction with the meator has been extensive during the 1996 academic year. I have spent a total of appmxima=ly

three weeks at the mentor's institution during the academic year. In addition, we communicate regularly by

electronic mail and telephone. We have collaborated on the dam analysis stage closely and have co-authored a

scientific paper announcing the research results that has been accepted for publication in the Astronomical Journal.

We are also in the process of developing proposals for observing time on various msu'uments to extend the research.

A multi-institutional research proposal was developed and submined to NSF. Although it received very good

reviews, the proposal was not funded. We intend to revise the proposal this summer and resubmit it in the fall. I

believe that the conaboration has been extremely viable.

*This P=n_jrL-ems Italpoz-_ should include infozzation for the pe_:iod 6/1/96 to 5/31/97.
JOVE ANNUAL P_SS REPORT: ACADEMIC YEAR 1996-97

III. EXTRAI4URAL FUNDING

Proposalm Av_: (At_ .h. s_jmmeuxe _,

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"Space Sciences Reso_ Travel,"

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NSF Extragaiacdc and Cosmology Division

1997-1999 atom=L,:: $ $384.846.00

_: Kentucky Space Grants Consortium

Pd. of lNt,t_ozmm_ : 7/01/97 - 6/30/98 amount: $ $3,761.00

"Collid/ng GaMx/es: A Search for C__nuir_ly Young Cra/axMs in Interacting Systems"

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JOVEFrdtyAduhm Dr. Benjamin K. Malphrus 

rndhth Morehead State University 

Cirde ga& academic yeu participating as a JOVE student researchar: 9394 

Has your participation in XlVE i- your carear choke? ayes CINa 

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Nation,.. Radio Astronomy OL.,ervatory

-----......_

Array _rm Center P.O. Box O, Socorro, New Mexico 87801-0387

J-- (505) 835-7000

' FAX (505) 835-7027

VIA The Very Large Array VLBA The Very Long Baseline Array

For Release:

9:20 a.m. CST, Tuesday, Jan. 16, 1996

J

Contact: Dave Finley (505) 835-7302

df inley_ccao, edu

New Galaxies From Old?

VLA Observations Strengthen the Case

Astronomers using the Very Large Array (VLA) radio telescope have found some of

the best evidence to date that small, new galaxies can form from material pulled out of

otder galaxies. The new observations senously weaken models of galactic evolution that

attempt to explain the various types of galaxies seen in the universe as the result of

different, but independent, processes. Steve Gottesman of the University of Florida in

Gainesville, Tim Hawarden of the Joint Astronomy Center in Hilo, Hawaii, Caroline

Simpson of Florida International University in Miami and Benjamin Malphrus of Morehead

State University in Morehead, Kentucky, presented the results today to the American

Astronomical Society meeting in San Antonio, TX.

The astronomers used the VIA, a facility of the National Science Foundation, to study

a galaxy system some 180 million tight-years distant in the constellation Centaurus called

NGC 5291. NGC 5291 is a peculiar spiral galaxy that appears to be interacting with a

nearby object called the Seashell. The VIA observations show a large, elongated cloud

of neutral hydrogen gas surrounding NGC 5291 and the Seashell.

Within that gas cloud there are several concentrations. These mostly coincide with

faint =knots" which were first seen on optical photographs taken twenty years ago with the

UK Schmidt Telescope in Australia for the ESO/SRC Southem Sky Survey. In a detailed

study at that time, using the 4-meter Anglo-Australian Telescope (AA'r) and the 65-meter

Parkes radio telescope, the knots were shown to be giant star-forming regions and the

system was found to contain an extremely large cloud of gas. Though details were lacking

then, astronomers suggested that the larger knots would turn out to be galaxies either in

- more -

The National Radio Astronomy. Observatory is a facility of the National Science Foundation,

operated under cooperative agreement by Associated Universities, Inc.,
Old Galaxies From New Page 2

the process of formation or recently formed from the matedal of the parent system.

Subsequently, similar suggestions were made about concentrations of material in the

"tidal tails" ejected by galactic collisions elsewhere in the sky, but it was not possible to

put the suggestions on a firm footing. This latest research, however, shows conclusively

that one of the knots in the NGC 5291 system is indeed a dwarf irregular galaxy similar to

the Mageilanic Clouds, companion galaxies to our own Milky Way. The knot of gas, in

which stars are being formed, has about 5 billion times the mass of the Sun.

"In order for it to be considered an independent galaxy, it must meet two conditions

-- its mass must remain gravitationally bound against its own kinetic energy and it must

remain bound against the gravitational effect of the primary galaxy. This knot in the NGC

5291 system has the stable properties, the required mass, and sufficient distance from the

remnant galaxies that, were it an isolated system, it would be classified as an actively starforming dwarf irregular galaxy," said Gottesman.

In addition, the researchers' analysis of the VLA observations indicates that several

other knots seen in the region probably are protogalaxies or young dwarf irregular

galaxies in various stages of development.

"It was a great thrill to see the VLA images confirm in detail the association between

the neutral hydrogen concentrations and the star-forming knnts which we predicted 17

years ago, and especially rewarding to see our suspicion that some knots would turn out

to be young galaxies so nicely verified," said Hawarden, who was part of the earlier

research team.

The new observations, combined with earlier evidence from interacting systems such

as Arp 105 and NGC 7252, strengthen the idea that galaxy collisions must be considered

an important agent of galactic evolution. "This is strong evidence that galaxies, especially

in clusters where they can interact with each other and with any hot medium present in

the cluster, can and do evolve in dramatic ways, including being able to form genuinely

young systems," Simpson said.

Maiphrus addea, =An important implication of this research is that genuinely young

galaxies may evolve from the debris formed of material tidally removed by galactic

interactions. We look forward to verification of this by the discovery of additional examples

of genuinely young irregular galaxies in interacting systems."

The astronomers used the VLA, a 27-antenna radio telescope west of Socorro, NM,

- more-
Old Galaxies From New Page 3

at times when its antennas were spacea in two different configurations in order to gain

both high resolving power and high sensitivity for the images. Observations of the radio

spectral line of neutral hydrogen allowed the astronomers to use the Doppler shift in

frequency of the received radio emissions to derive information about the velocity of the

gas in different parts of the cloud.

Reduction and analysis of the data were made possible by a grant received from the

National Aeronautics and Space Administration Joint Ventures in Research (NASAJOVE) Project. Initial observations were made with the Very Large Array, an instrument

of the National Radio Astronomy Observatory, a facility of the National Science

Foundation operated under cooperative agreement by Associated Universities

Incorporated. Digitized image and object positions were obtained using the Guide Star

Astrometdc Support Program deve, toped at the Space Telescope Science Institute

(STScl), which is operated by the Association of Universities for Research in Astronomy,

Inc., for NASA. This research has made use of the NASNIPAC Extragalactic Database

(NED) which is operated by the Jet Propulsion Laboratory, California Institute of

Technology, under contract with the National Aeronautics and Space Administration.

For More Information Contact:

Dr. Benjamin K. Malphrus

Dr. Caroline Simpson

Dr. Tim Hawarden

Dr. Steve Gottesman

###

(606) 783 2212

(305) 348 1565

(808) 935 0407

b.malphr@ msuacad.morehead-st.edu

simpsonc @ galaxy.fiu.edu

hawarden @jach .hawaii.edu

sgottes @ II.iac.es
Radio and Optical Images of the 5291 Region

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RIGlrr ASCENSION (B1950)

A Young Galaxy Emerges From the Debris of a Galactic Collision

in this image, contours (lines) representing the strength of radio emission from neutral atomic hydrogen are

superimposed on an optical image (greyscale). "Knot B" is the optical object that coincides with a large

concentration of hydrogen gas, and has been shown by detailed analysis to be an independem, star-forming

galaxy. The gas from which it formed is believed to have been ejected by the interaction of the older galaxies,

NGC 5291 and the Seashell.

Photo Credit: Steve Gottesman, Tim Hawarden, Caroline Simpson, Benjamin Malphrus; ESO/SRC Sky Survey

and Space Telescope Science Institute; and NRAO/AUI.
NGC 5291: Implications for the Formation of Dwarf Galaxies

Benjamin K. Malphrus

Department of Physical Sciences, Morehead State University, Morehead, KY 40351

b.malphr_morehead-st.edu

Caroline E. Simpson

Department of Physics, Florida International University, Miami, Florida 33199

simpsonc_fiu.edu

S. T. Gottesman

Department of Astronomy, University of Florida, Gainesville, Florida 32611

gott@astro.ufl.edu

Timothy G. Hawarden 1

Joint Astronomy Centre, 660 North A'ohoku Place, Hilo, Hawaii 96270

hawarden@jach.hawaii.edu

Received ; accepted

To appear in The Astronomical Journal

1Royal Observatory, Blackford Hill, Edinburgh EH9 3H J, United Kingdom
-2-

ABSTRACT

The possibleformation and evolution of dwarf irregular galaxies from

material derived from perturbed evolvedgalaxiesis addressedvia an H I study

of a likely example,the peculiar system NGC 5291. This system, located in the

westernoutskirts of the cluster Abell 3574,containsthe lenticular galaxy NGC

5291which is in closeproximity to a disturbed companionand is flanked by an

extensivecomplexof numerousknots extending roughly 4_north and 4_south

of the galaxy. In an initial optical and radio study, Long'moreet al. (1979)

showed that these knots have the spectra of vigorous star-forming regions, and

suggested that some may in fact be young dwarf irregular galaxies.

High resolution 21-cm line observations taken with the VLA are presented

here and reveal that the H I distribution associated with this system encompasses

not only the entire N-S complex of optical knots, but also forms an incomplete

ring or tail that extends approximately 3 _ to the west. The H I associated

with NGC 5291 itself shows a high velocity range; the Seashell is not detected.

The formation mechanism for this unusual system is unclear and two models

- a large, low-luminosity ram-swept disk, and a ram-swept interaction - are

discussed.

The H I in the system contains numerous concentrations,mostly along the

N-S arc of the star-forming complexes, which generally coincide with one or

more opticalknots; the larger H I features contain several x 109 M® of gas.

Each of the knots iscompared to a set of criteriadesigned to determine ifthese

objects are bound against their own internalkineticenergy and are tidally

stable relativeto the host galaxy.

An analysisof the properties of the H I concentrations surrounding the

opticalstar-forming complexes indicates that at leastthe largestof these is
3

a bound system; it also possesses a stellar component. It is suggested that

this object is a genuinely young dwarf irregular galaxy that has evolved from

the material associated with the system and that this entire complex contains

several proto- or young dwarf irregular galaxies in various stages of development.

We are therefore witnessing the early evolution of a number of genuinely young

galaxies. Given the evident importance of the NGC 5291 system as a "nursery"

for young galaxies, careful modeling is required if we are to understand this

remarkable galaxy.

Subject headings:
-4-

1. Introduction

NGC 5291 lies at _ = 13 h 47 TM 24_.3, 5 = -30 ° 24' 26" (J2000), in the western parts of

the cluster Abell 35742 (AbeU 1958) of which it is probably a member. We adopt a value

for H0 of 75 km s -1 Mpc-1; the cluster recession velocity of 4350 km s-1 (e.g. Richter 1984)

then implies a distance of 58 Mpc. Pedersen et al. (1978) presented and briefly discusseddeep images of the system taken with the ESO 3.6m telescope, drawing attention to the

immense complexes of optical knots which extend several galactic diameters to the north

and south and hypothesizing that these are H II regions (or at least, sites of recent star

formation) from their blue colors. In the Second Reference Catalog of Bright Galaxies (de

Vaucouleurs et al. 1976) NGC 5291 is classified as a peculiar elliptical (Ep?) with a nearby

companion. Longmore et al. (1979, hereafter L79), using deep IIIaJ plates from the UK

Schmidt Telescope for the Southern Sky Survey, reclassified NGC 5291 as SA.0+.

Table 1 summarizes the properties of the NGC 5291 system, while Figure 1 shows a

B-band image of NGC 5291 taken by Pedersen et al. (1978) with the ESO 3.6m telescope.

The main bodies of the galaxies NGC 5291 and its companion (dubbed "the Seashell"

by L79 because of its appearance) are themselves relatively unremarkable. The overall

lenticular morphology of the former is evident in the bulge-disc structure, and its late

lenticular sub-type in the weak, smooth, possibly spiral, structure and dust lane evident to

the NE. The Seashell is basically smooth in texture, and therefore probably also lenticular

in underlying type; perhaps slightly earlier than NGC 5291, since no dust structure is

visible. It displays dramatic evidence of its tidal distortion, in its contorted disk morphology

and sharply defined edge. Nevertheless, the most unusual feature of this double system is

not so much the morphology of the main bodies of the galaxies but the clearly-associated

2a.k.a. Shapley 1346-30 (Shapley 1936), IC 4329 (de Vaucouleurs & de Vancouleurs 1964),

and Klemola 29 (Klemola 1969).
-5-

swarmsof knotty condensations,ranging in sizedown to the resolution limit of the image,

and extending ,-_ 4' both north and south of the pair.

EDITOR: PLACE FIGURE 1 HERE.

EDITOR: PLACE TABLE 1 HERE.

Longmore et al. (L79) obtained optical spectra of NGC 5291, the Seashell and of a

number of the outlying knots, confirming that these last are indeed the locations of vigorous

star formation as suggested by Pedersen et al. (1978), and have the spectra of H II regions.

Longmore et al. also made 21-cm observations of the system, using the 64m Parkes (HPBW

-- 15') and 100m Effelsberg (HPBW = 9') telescopes, which revealed that -,_ 5 × 101°Mq)

(H0 = 75 km s-_ Mpc -_) of H I gas was present in the complex. The velocity ranges both of

the optical features and of the H I are > 650 km s -1 and are centered on that of NGC 5291,

with which they are clearly associated. This H I distribution was not resolved, however,

although the H I centroid could be seen to be offset ,,_ 1_5 to the west of the optical system

(primarily, it is now apparent from our new data, as a consequence of the source geometry).

In their paper, L79 drew attention to the luminosities and sizes of the brighter H I!

objects in the complex and particularly pointed out that they appeared to have all the

properties of dwarf irregular galaxies, and that, if these are bound entities, they are

eventually likely to be lost from the parent galaxy and will assume an independent existence

as young dwarf systems. Two models describing the formation of these objects were then

postulated, namely, ram-sweeping and local compression of a pre-existing, very extended

H I disk and consequent collapse of the denser concentrations into star-forming cloud

complexes, or the formation of these complexes from clumps of material tidally removed

from the main bodies of the galaxies by the effects of the interaction.
-6-

Longmore et al. discussed the overall properties of the system and noted the very

evident interaction between NGC 5291 and the Seashell. However they pointed out that

the high relative velocity of the two galaxies (,-_ 600 km s-_, in an apparently retrograde

sense) which they measured made the creation of such massive and extensive tidal features

seem unlikely. The asymmetric, curved optical structure and the geometrical offset of the

H I centroid, together with the system's location in the northwest edge of a cluster then led

them to suspect the presence of ram-sweeping. They speculated that NGC 5291 initially

possessed a very extended, tenuous disk of H I, and suggested that this disk is now being

compressed from the east as the galaxy falls into the Abell 3574 cluster and encounters an

intracluster medium. Instabilities triggered by this ram-sweeping process would then, they

suggest, have given rise to the observed star-forming complexes, while the sweeping-up and

compression of the H I would give rise to the asymmetric distribution they observed.

To investigate further these scenarios, and the intriguing possibility that the starforming objects in the extended complex are, indeed, dwarf galaxies in the process of

formation, high resolution H I observations were taken using the Very Large Array (VLA)

Radio Telescope 3 and are presented here. The observations described in this paper of the

system, the debris field, and its contents show that it is even more complex and unusual

than previously suspected.

In section 2 of this paper, we present the observational procedures and data reduction;

section 3 contains a description of the H I distribution and kinematics, and section 4

discusses the analysis and interpretation of the results, including discussions of both the

primordial disk and interaction hypotheses. Conclusions and a summary are presented in

3The VLA is operated by The National Radio Astronomy Observatory; the National

Radio Astronomy Observatory is a facility of the National Science Foundation operated

under cooperative agreement by Associated Universities, Inc.
section 5.

-7-

2. Observations and Data Reduction

High spatial resolution spectral line observations of the 21-cm emission from the region

of NGC 5291 were made in 1989 by STG and R. Byrne with the Very Large Array radio

telescope (VLA) in its CnB and DnC hybrid configurations, using a 64 channel spectrometer

with a total bandwidth of 6.25 MHz. The resulting channel separation of 97 KHz provides

velocity resolution of 25.6 km s-t: the observations were made at a central velocity of 4386

km s-l. Data were collected for two polarizations, right and left circular, which were then

averaged together to enhance the signal-to-noise ratio in the final images.

The hybrid configurations have a long north arm to maintain resolution at extreme

southern declinations where projection effects for the beam are large. At the declination

of NGC 5291 the more extended CnB array provides spatial resolution of 14" x 13" while

the compact DnC array, with lower spatial resolution (50" x 39") is more sensitive to weak

extended emission. A third set of data was produced by combining that from both arrays -

this takes advantage both of the higher resolution of the CnB array data and of the higher

sensitivity of the DnC array observations. The spatial resolution of the combined data set

(hereafter referred to as the combined array data, or the C+D array data) is 26" x 15". The

observational parameters for all three sets of data are shown in Table 2.

EDITOR: PLACE TABLE 2 HERE.

Calibration and editing of the data were performed using the AIPS data reduction

package available from NRAO. The phase and amplitude response of the receiving system

were calibrated using the continuum sources 1354-152 and 1313-333 for the CnB array
-8-

observations, and 1313-333 for the DnC array observations. The calibrators were observed

every thirty minutes for the duration of the observations. These calibration sources and the

instrumental bandpass were in turn calibrated for radio frequency flux using the primary

standard 3C 286.

The data from each configuration was edited and calibrated independently and -

converted to separate high resolution and high-sensitivity image cubes; the two data sets

were also combined in the uv-plane to produce the C÷D combined array dataset.

The data reduction was complicated by the presence of an internal interference spike

at 1400 MHz, uncomfortably close to the observed frequency (1400.8 MHz) of the H I

hyperfine transition at the systemic velocity of NGC 5291. Calibration involves the use of a

continuum data set which is normally created by averaging together the central two-thirds

of the channels in the bandpass. The continuum data set created during our observations

was therefore affected by the interference spike, which was present in a few of the central

channels. Rather than attempting to identify and remove the contaminated data piecemeal,

a new interference-free continuum data set was created by identifying 21 interference-free

channels (those well away from the problematic frequency) in the line dataset and averaging

them in the uv-plane.

After calibration, the line data were examined and edited. The channels affected

by the interference spike were easily identified and the affected data were removed by

"clipping" data points above a specified value determined from an examination of the

unaffected channels. This process minimized the removal of uncontaminated data points

and hence resulted in the removal of very few data points (,,_ 2% of the total) in unaffected

channels. The contaminated channels, however, suffered the loss of approximately half of

the data, thus degrading their signal-to-noise. Fortunately, not more than three channels

were severely affected, due to the narrow frequency range of the interference spike. The
9

poorer quality of the data from the heavily clipped channelsresulted in somelossof signal

during the blanking and integrating processes(describedbelow), and slightly reducedthe

column densitiesand H I massescalculated from the integrated dataset.

The uv data set was Fourier transformed to produce images of the intensity distribution

of the source for each channel. The data cube of channel maps resulting from this process

includes not only the 21-cm line emission from the observed source, but also the continuum

emission from other sources. Continuum estimation was performed by combining channels

which were free of line emission from both ends of the data cube, thirteen from the low

frequency end and eleven from the high frequency end. This averaged continuum map was

then subtracted from each channel of the cube.

Since the images are produced using a fast Fourier transform, any unsampled points

in the uv-plane are automatically set to zero. In addition, the finite nature of the uv data

set produces a truncation effect, so that the fast Fourier transform process results in a

synthesized beam with extensive sidelobes: the "dirty beam." The continuum-subtracted

data cube, consisting only of 21-cm line emission from the source, is actually a representation

of the source brightness distribution convolved with the dirty beam. Confusion caused by

the dirty beam was corrected by using the AIPS CLEAN routine (HSgbom 1974, Clark

1980). The resulting point-source model was then convolved with the "clean beam," a 2-D

Gaussian with the same full-width half-maximum (FWHM) as the dirty beam, to remove

grating responses and sidelobes.

The data cubes were CLEANed down to 2 x the average r.m.s, noise (a) as determined

by a statistical analysis of the signal-free channel maps. Synthesized beamsizes representing

the effective spatial resolution of the Gaussian CLEAN beams were calculated for all three

data sets; these values are provided in Table 2. The average r.m.s, noise after CLEANing

was determined to be 0.60 mJy per beam solid angle for the CnB array data, 0.71 mJy per
- 10-

beam solid anglefor the DnC array data, and 0.56for the combinedarray data (Table 2).

After the data cubeswereCLEANed, final imaging wasperformedby the integration

of signalfrom ,,_ 40 contributing channels. This was done using the AIPS routine MOMNT,

which conditionally blanks the data cube using a mask created by smoothing the data

in both velocity and space (c_, 5) and then integrates the blanked dataset. Blanking is

performed in an attempt to isolate the signal from the noise by suppressing the noise.

The data for NGC 5291 were blanked and integrated using a mask created by Hanning

smoothing in velocity, and convolving in right ascension and declination with a Gaussian

corresponding to twice the FWHM of the clean beam. The blanking and integrating levels

were set to approximately 1.5 times the r.m.s, noise level on the unsmoothed data. Moment

maps representing the H I column density (integrated flux) distribution (0th moment),

velocity field (1st moment), and velocity dispersion (2nd moment) were created by this

process.

3. Results

3.1. H I Spatial Distribution

Moment maps from the high sensitivity DnC array data, the high resolution CnB

array data, and the combined C+D data were produced using the method described above.

Figure 2 shows a grayscale image of the integrated H I flux distribution from the CnB array

data overlaid with the 2a contour level of the H I distribution from the DnC array data.

We have indicated the positions of the original optical knots identified by L79 (A-H), as

well as the discrete H I features (I-M) detected in the VLA observations that also appear

to be associated with optical knots identified from either the optical image in Figure 1 or
-11-

the Digitized Sky Survey image4. Also identified are the locationsof NGC 5291and of the

Seashell. The H I forms what appears to be an incomplete ring structure extending about

9!9 north-south (163 kpc) and 5_6 east-west (93 kpc).

EDITOR: PLACE FIGURE 2 HERE.

The single-dish observations by L79 found the centroid of the H I to be offset ,,_ 1._5 to

the west of the optical objects. This appears to be an effect of the presence of the westward

arc, which was unresolved by the 9' and 15' beams of the Effelsberg and Parkes telescopes.

To test this, we smoothed the integrated intensity image from the present DnC array

observations with a 9' Gaussian to replicate the resolution of the Effelsberg observations.

This indeed produced a smooth distribution with the peak intensity located ,,_ 1'.5 to the

west of NGC 5291.

A grayscale image of the H I integrated flux from the combined C+D array data is

shown in Figure 3. The optical image from the Digitized Sky Survey (derived from a UK

Schmidt IIIaJ plate) overlaid with these H I contours is shown in Figure 4. The H I is highly

structured on scales at least down to the CnB beam size and many of the concentrations

are clearly associated with optical knots.

EDITOR: PLACE FIGURE 3 HERE.

EDITOR: PLACE FIGURE 4 HERE.

The spatial association of the H I concentrations with the larger optical knots is very

striking. Figure 3 shows that the H I distribution in the complex is generally clumpy; the

4Obtained using Skyview; see acknowlegements
0 200 400

-3004

O6

0

tt'b

o's

"" 08

Z

@

<

Z I0

12

14

16

•--, +

|

- =. [,_. ;

13 4445 30

"L. . t-i-.

Fig. 2. Grayscale image of HI integrated intensity from BnC array data, with 2or contour from CnD

array data overlaid. BnC array beamsize (14" x 13') indicated by upper ellipse in lower right comer;

CnD array beamsize (50" × 39") indicated by lower ellipse. Crosses indicate objects listed in the HST

Guide Star Catalog. Optical knots indicated by letters.
0 200 400 600

Z

©

b.,

<

Z

,.-.1

r,.)

-30 02

O4

06

08

10

12

14

16

+

" "5 . . ,

13 44 45 30 15 00

RIGHT ASCENSION (B 1950)

Fig. 3. Grayscale image of the HI integrated intensity from BnC+CnD combined array data. Contour

levels are 1.1 (2o,), 5, 10, 15, and 20 x 1020 atom crn -2. The beamsize (26" x 15') is indicated by

the ellipse in the lower right comer. Crosses indicate objects listed in the HST Guide Star Catalog.

Optical knots indicated by letters.
5 10 15

O_

Z

©

[.-,

<

Z

.2

rO

-30 02

04

O6

08

10

12

14

16

o •

°

RIGHT ASCENSION (B 1950)

Fig. 4. HI integrated intensity from the BnC+CnD combined array data superimposed over the digitized

optical image taken from the UK Schmidt lIlaJ Sky Survey plate. Contour levels are 1.1 (2tr), 5, 10, 15,

and 20 × 102o atom cm -2. The beamsize (26" x 15') is indicated by the ellipse in the lower left comer.

Crosses indicate objects listed in the HST Guide Star Catalog. Optical knots indicated by letters.
- 12-

amount and location of H I associatedwith the optical knots observedby L79 are clearly

visible in Figure 4. The greatestconcentration of H I is associatednot with NGC 5291

itself, but with optical Knot B. More detailed inter-comparison of the optical and H I images

shows that many of the H I features and clumps have underlying optical knots. Several of

these - those associated with the H I lying north of Knot A and also to the southwest of

Knot B, and possibly with Knot M as well - have been observed spectroscopically 5 and

confirmed to be emission line regions (H II complexes) like Knots A to H. The observed H II

regions have optical velocities in good agreement with those of the associated H I features

(Hawarden et al. 1997), while the rest are very similar in appearance in Figure 1 to the

confirmed H II complexes.

The existence of the westernmost H I emission, including the concentrations labeled as

knots K and L, was not previously suspected; examination of the optical image (Figure 1)

reveals faint optical knots coinciding with the H I features I-M as well. Knots I, J, and M

appear to be associated with several faint optical features rather than one large one as for

the other knots. However, we note that these objects could be chance superpositions of

faint background galaxies; spectroscopy is needed to verify these associations.

A strong, highly resolved H I feature (clearly visible in Figure 3) lies _-, 0_5 west of a

point about a third of the way from the nucleus of NGC 5291 to the brightest northern

knot, B. There is no single bright optical feature underlying this H I concentration, but it

does appear to be associated with a swarm of faint optical knots on Figure 1, which also

have the appearance of H II complexes.

Some H I, ,,_ 20% of the total amount in the system, is evidently associated with the

main body of NGC 5291, most of it lying slightly to the west and north of the center of

5by the late Dr. David Allen at the AAT
- 13-

the galaxy (Figure 3). The associationof this material with the galaxy is confirmed by the

correspondence of its flux-weighted systemic velocity, 4370 km s-1 (see section 3.3, with

that of the galaxy as determined from optical observations (4335 km s-1, L79; 4330 km s -I ,

Hawarden et al. 1997).

While some H I also lies in a similar projected position relative to the Seashell, this

material has a velocity ,,, 4380 km s -1, several hundred km s -1 too high to be associated

with that galaxy (which has cz = 3950 km s-l: Duc 1995 or 3730 km s-l: L79; see below).

The velocity range covered in the VLA observations is ,,_ 3590 to 4870 km s-1 and includes

both these values; however no H I was detected near these velocities. Evidently the Seashell

contains little or no H I at present: we derive (see below) an upper limit to its H I mass

(single-channel 5a detection) of 5.7 x l0 T M®.

Perhaps the Seashell was an H I-poor lenticular, a classification which is consistent

with its relatively smooth (if distorted) structure (even on the UV image of L79) and also

its moderately red colors (Daly et al. 1987). If any H I it may initially have possessed was

located in the outskirts of the system it would probably have been lost in the encounter

with NGC 5291, but the apparent absence, anywhere in this system, of detectable H I at

the velocity of the Seashell strongly suggests that this was not the case. Using the cooled

grating spectrometer CGS4 on the 3.8m UK Infrared Telescope (UKIRT), we have secured

a K-band spectrum covering the first overtone (A - 2.3#m) bandhead of CO in stellar

atmospheres. This spectral feature is unusually weak in the Seashell, which implies that

it cannot recently have housed a nuclear starburst since strong nuclear CO absorption in

the atmospheres of red supergiants is to be expected in the aftermath of such an event.

Together with its weak optical emission lines, this further argues against there having been

a significant amount of H I in the central parts of the Seashell.
- 14-

The galaxy located in the southwest part of the overall H I complex is number 435

in Richter's (1984) list of galaxies in the cluster and surrounding area. He classifies it Sc;

from Figure 1 we refine this to SA(s)c. Richter gives a heliocentric velocity of 4088 km

s-_, strongly suggesting that it is a member of the cluster. While its H I component is well

detected on our images among the gas associated with the southern end of the NGC 5291

complex, its velocity is quite different, so that no confusion arises. Evidently Richter 435

has no connection with the NGC 5291 complex.

Five arc-minutes to the northeast a second prominent galaxy is also included in the

VLA primary beam but is not detected in H I. This is a barred spiral listed as number

446 by Richter, who gives a radial velocity of 4409 km s -1, in excellent agreement with the

L79 velocity of 4420 km s-_ and a more recent AAT velocity of 4414 km s-_; its velocity

is clearly close to that of NGC 5291. Richter classifies this system Sd, which suggests that

it should be H I-rich and should have been detected in our images. However, scrutiny of

Figure 1 shows a generally smooth structure, except for some curious lateral spurs attached

to the bar, suggesting that R446 is actually a lenticular or very early spiral: we propose a

classification PJSB(s)0/a. Such a system would be quite likely to contain little H I.

Figure 5 shows the radio continuum emission as determined from those channels free of

line emission. There is continuum emission associated with the optical body of NGC 5291

as well as that of Knot B which is presumably due to ionization from O and B stars. The

low level (3a) of the detected emission precludes quantitative analysis.

EDITOR: PLACE FIGURE 5 HERE.
-30 05

15

10

oo 13 44 30 oo

RIGHT ASCENSION (B1950)

Fig. 5a. Individual channel maps produced from the CnD array observations. Contour levels are

at 2, 5, 10, 15, and 20o'. Heliocentric velocities are listed in the upper right of each image.
-30 05

10

15

-30 05

I0

15

-30 05

g

z

o 10

z

-30 05

10

15

-30 05

I0

15

0

t_ *

13 44 30 00

0

_ °0 • o

I |

., 39 3.3 

0 "

• • @

l II I

Fig. 5b. Individual channel maps produced from the CnD array observations. Contour levels are

at 2, 5, 10, 15, and 20o'. Heliocentric velocities are listed in the upper right of each image.
- 15-

3.2. H I Column Densities and Masses

Figures 2 and 3 represent the integrated intensity (column density) of the H I flux from

the system. The column density of the H I along the line of sight for a given position (a, 5)

may be determined for a source by integrating the brightness over all velocities using the

following expression (Mihalas & Binney 1981):

Nsi(a, 5) = 1.82 x 10 is /? Ts(a, 5) dv, (1)

OO

where TB is the brightness temperature in Kelvin and v is the velocity in km s-1. The peak

column densities found for the identified features (the galaxies and knots) on the moment

maps are listed in Table 3. These values were determined using the DnC array data, which

is most sensitive to extended emission. The highest column density in the entire complex,

12.6 x 102° atoms cm -2, is associated with Knot B. The peak column densities for NGC

5291 and the H I Concentration are 10.7 x 10 20 and 10.6 x 1020 atoms cm -2, respectively.

Peak column densities for the rest of the labelled knots range from 1.4 x 10 _° to 7.4 x 102°

atoms cm -2. The detection threshold (2a level) is 1 x 102° atoms cm -2.

The integrated flux from the H I gas may be found by integrating equation (1) over the

solid angle subtended by the feature, and expressing the brightness temperature in terms of

the observed flux S(v). The H I mass may then be calculated as follows (Mihalas & Binney

1981):

Mm 2.36 x 105 D 2 f_ S(v) dr, (2)

J--oo

where Mm is expressed in solar masses, D is the distance in Mpc, S(v) is the flux in Janskys

summed over the area of the feature, and v is velocity. The areas used to determine the

masses for each knot are indicated in Figure 6, and the corresponding calculated H I masses

are listed in Table 3.

EDITOR: PLACE TABLE 3 HERE.
- 16-

EDITOR: PLACE FIGURE 6 HERE.

The H I massesassociatedwith Knot B and the H I Concentration are roughly

comparable:2.48x 109M® and 2.03 x 109 M® respectively. The H I mass associated with

NGC 5291 is 1.60 x 109 ME). This value represents only 21% of the total H I mass of the

complex (see below); over three-quarters of the total H I mass is located in the extensions.

The H I masses of the other knots range from 7 x l0 T M® to 9 x 108 M® (Table 3).

The total H I mass detected with the VLA for the entire complex is 1.80 x 10 l° ME).

This is approximately 36% of that detected in the single-dish observations by L79 (Table 1).

Our estimate does not include the H I mass of Abell 3574 0435 (9.92 x 108 M®) which

must have been included in the large beams of the telescopes at Parkes (15 t FWHM) and

Effelsberg (9 °) used by L79. This would only add 5% to the total H I mass, however, and so

cannot account for the discrepancy.

It is well known that single-dish spectra are prone to substantial instrumental effects

that make them unreliable for weak extended emission-line spectra. The Effelsberg data

may be an overestimate of the H I present. Employing a very wide bandwidth, L79 were

observing for broad and weak spectral features, which is notoriously difficult with an

autocorrelation receiver. Indeed the data taken by the Parkes radio telescope were not used

for this reason. Baseline curvatures can add to or subtract from apparent line strengths,

especially on very broad lines such as that from the NGC 5291 complex. It is therefore

possible that the discrepancy between the masses determined from the VLA and single-dish

observations is somewhat less than reported. It is questionable, however, whether the entire

difference between the VLA and single-dish fluxes could be attributable to baseline errors.

Examination of the H I spectra in L79 suggests that an overestimate of around 40% is

the most that could reasonably be attributed to an unrecognized baseline rise around the

systemic velocity of 4400 km s -1. New, high-sensitivity single-dish observations, secured
-17-

with a systemhaving stable baselinesand a beam at leastas large asthat set by the VLA

minimum spacing,would clearly be most valuableto resolvethis problem.

There are four possibilities for accounting for the "missingH I", more than one of

which could be simultaneouslytrue. The singledish measurecould indeed be a 30% to

40%overestimate,asdiscussedabove. It is also possiblethat someof the H I could be so

extendedin velocity and/or spaceasto fall below the surfacedensity detection threshold

of the observations.We note, however,that if the "missingmass" were to fill in the ring,

then the H I surfacedensity would be approximately 2.0 × 1021cm-2, which is well above

the detection threshold of the DnC array.

3.3. Kinematics

Individual velocity channel maps of the D array data in a 15 _ x 15' area are presented

in Figure 7. It is clear that H I in the NGC 5291 complex has an overall ordered velocity

structure, with velocities varying (for the most part) in a regular manner from low values

in the north to high in the south.

EDITOR: PLACE FIGURE 7 HERE.

The cumulative velocity field of the gas can be determined by calculating the

intensity-weighted mean velocity of the gas at each position (a, (f). This is accomplished

by taking the first moment of the column density relationship (equation 1) with respect to

velocity as follows:

f_°°ooTB (a, _) v (C_,_) dv

(v(c_,J)} = f__ooTB(a, _) dv

(3)

Figure 8 shows the first moment map of the complex. The isovelocity contours are

separated by 25 km s -1. The wide N - S velocity range is evident. The maximum velocity,
- 18-

in the south of the complex, is 4750km s-t; the minimum, in the north, is 4040km s-_,

giving a (large) total velocity rangeof 710km s-1. The flux-weightedheliocentric velocity

of the gasassociatedwith NGC 5291itself is 4370km s-I, whereasthat for the entire

complexis 4406km s-1. The differencein the flux-weighted velocities show that the gas

density is not symmetrically distributed in velocity spacewith respectto the galaxy.

The velocity structure, though necessarilysimplified in this figure by averaging,

neverthelessshowsconsiderablecomplexityjust north and south of the main body of NGC

5291: here the isovelocity contoursare much closer-spacedthan in the outlying regions,

and considerableE-W velocity shearacross,e.g. the H I Concentration of Figure 2 is also

apparent. The overall behavior is not very dissimilar to that which would be expected from

a galaxy seen edge-on, but with additional complexities.

The general velocity trend apparent in the main, eastern arc of H I is also visible in the

western arc as well, but here the gradient appears roughly linear overall. The velocity of

the (northern) knot L in the western arc is ,,_ 145 km s-1 higher than the H I in the eastern

arc at the same N-S position. In the southern part of the western arc, an opposite trend is

(barely) apparent: knots J and K have (average) velocities ,,_ 60 and 50 km s-1 lower than

the H I in the corresponding parts of the eastern arc.

EDITOR: PLACE FIGURE 8 HERE.

The spatial distribution of the velocity dispersion of the H I is shown in Figure 9.

The velocity dispersions are calculated for each position by taking the second moment of

f:% Ts(a, ) dv (4)

equation 1 with respect to velocity:
0 50 100

-30 02

04

06

0

m 08

Z

O

<

Z 10

12

14

16

+ + +

A

B

+

+

+

NGC 5291

+

+

Seashell

+

+

13 4445

+

++

:1

K

+++

C Abell 3574 0_135

D + 'h --

4

+

II

1 1 I 1

30 15 190

RIGHT ASCENSION (B 1950)

Fig. 7. Isovelocity contours superimposed on the velocity dispersion image (second moment map)

produced from the BnC+CnD combined array observations. The contours are 10, 25, 30, 50, 75, 100

km s-l; the velocity resolution is 21 km s-l.
.025

_._ .015olijt I

.005 Jt !

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

"°z5f'.o2KnoUt''_ t'' 'C t _'' t ' ' _ !l_

.015 -

X

_.. .Ol

.005

0 -_--F-Vq--I--T i--F-_-T-I i

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

°25I.o2_J ' I Knot ' ' 'H i ' ' ' I ' ' ' I ' ' I

_-"-'_x.015 1

.ol -

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

.025 ,

.O2

.015

X

_ .01

.005

.025

.O2

.015

X

.ol

.005

.025

.O2

._..015

X

-= .Ol

.005

HI Concentration

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

NGC 5291

4000 4200 4400 4600 4800

Velocity (Ve) (km/sec)

Knot K

I=,_-_TU--_==i--_==::_=_: i' , -i==Uq--=?U---=

4000 4200 4400 4600 4600

Velocity (Vo) (km/sec)

Fig. 8a. Velocity profiles for components of NGC 5291 complex. Vertical axis (flux in Janskys)

drawn to same scale for all six objects, with a peak flux of 0.025 Jy.
.o,i

>¢

= .005 --

0

.01

v

X

.oo5

.01

><

.005

E

0

Knot C

-- .01

_=_

v

X

-- = .005

E

0

Iii I iii t i IiI i t II _, , I_

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

I I lKnot I I IJ [ I I I ] I 1 ' L _ I _ ]

! .01

X

- 2 .005

i I i ,, t, , I I t III ,, l

4000 4200 4400 4600 4800

Velocity (Vo) (kin/see)

L, , i , , , [ , , , l , , 1 I ! , , I _'

- Knot L

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

.01

X

= .005

E

- Knot D

_t

4000 4200 4400 4600 4800

Velocity (Vo) (kin/see)

Knot M

4000 4200 4400 4600 4800

Velocity (Vo) (kin/see)

- Knot I

4000 4200 4400 4600 4800

Velocity (Vo) (km/sec)

Fig. 8b. Velocity profiles for components of NGC 5291 complex. Vertical axis (flux in Janskys)

drawn to same scale for all six objects, with a peak flux of 0.0125 Jy. Note that the vertical scale is

therefore half of that used for Fig. 8a.
- 19-

EDITOR: PLACE FIGURE 9 HERE.

It can be seen in Figure 9 that there are two regions of very high dispersion, on

the order of 100 km s -1. These regions, one encompassing both NGC 5291 and the H I

Concentration, and one associated with Knot D, imply the presence in the line of sight of

bodies of gas with widely ranging velocities (see Figure 11). These are further discussed

below.

4. Discussion

4.1. Physical Nature of the System

The obvious, strong, distortion of the Seashell, presumably by interaction with NGC

5291, immediately suggests that the far-flung outlying structures in the system were caused

by tidal effects from this interaction. However the large velocity difference between the two

galaxies measured by L79 (640 km s-i), and its apparently retrograde sense, made the great

amplitude of the resulting disruption difficult to understand in terms of tidal effects. This

led them to seek alternative hypotheses for the origin of the outlying features.

Since the major problem with the tidal disruption scenario was the difficulty of moving

so large a mass of material to such large radii they hypothesized, instead, a pre-existing,

very extensive, and presumably primordial H I disk. This was a logical extrapolation of the

properties of several other H I-rich early-type systems listed by L79, and analogous to the

then-undiscovered Malin 1 (Bothun et al. 1987; see also Sprayberry et al. 1995 for more

details of the properties of this class of galaxies).

Longmore at al. then proposed two trigger mechanisms for the intense but localized

star formation activity seen in the outlying complexes. The first suggestion was that NGC
- 20-

5291has sufferedan almost orthogonal, off-center,penetration by a companion galaxy

(though probably not the Seashell)which has causedan eccentric kinematic density wave

to propagatethrough the disk, producinga ring galaxy with offsetnucleus (see,e.g., Lynds

& Toomre 1976;Theys & Spiegel1976). They tentatively identified Richter 446 (to the

northeast) as a potential culprit, but did not pursue the hypothesisbecausethe ring was

incomplete.

The secondtrigger mechanismwas suggestedto L79 by the location of NGC 5291in

the outskirts of a galaxy cluster, the concentrationof the H II complexesin an arc convex

toward the cluster and centeredon the galaxy and by the westwardoffsetof the centroid

of the H I emission. Theseled L79 to speculatethat the postulated H I disk is being

ram-swept,more or lessfrom oneedge,asthe galaxy movesmostly eastwardsthrough an

intracluster medium, and that it is this processwhich has triggered star formation, by

compressionof the previously too-tenuousH I disk.

We have noted that the H I offset, at least, now appears to reflect the detailed

distribution of the gas as seenat low resolution. The kinematics, but especially the

morphology of the H I in this system as revealed by the higher resolution VLA data

presented here, encourage us to reinstate as a possible scenario the original interpretation of

the outlying features as the products of tidal disruption consequent on an encounter, most

likely with the Seashell. The ring-arc seen in the H I may represent tidally removed debris

along the path of motion of the component galaxies of the system, similar to the Magellanic

stream. Alternatively, the arms, counter-arms and bridges of an interaction, first discussed

by Toomre & Toomre 1972 are seen at very large projection.

We also note that the western H I arc repairs the "incomplete ring" noted by L79 as

evidence against a possible orthogonal penetration by some galaxy other than the Seashell.

As they suggested, Richter 446 is the most probable candidate as it does appear poor in gas
- 21-

and possiblydisturbed, as might befit a systemwhich haspassedthough, and beenswept

cleanby, a giant neighbor.

In the rest of this section we discussthe casefor ram-sweeping,and revisit the

"primordial disk" and "tidal disruption" scenariosfor the creation of the outlying complexes

in the NGC 5291system,and thus of the candidate "young galaxies" lying within them.

There is supporting evidencefor both creation models, as well as for ram-sweeping. Each

of the two formation scenarios, however, has limitations based on analysis of the existing

optical, radio, and x-ray data.

._.1.1. Ram Sweeping

As NGC 5291 is located in the northwest part of the Abell 3574 cluster, ram-sweeping

would be expected to produce compression along the leading (east) edge, assuming that

the system is moving toward the center of the cluster, located to the southeast. On all

hypotheses one would expect to find that the star formation regions (SFRs) are associated

with H I concentrations. If ram-sweeping is occurring, one further expects that since the

SFRs are presumably of higher density than the less concentrated H I the latter will tend

to be displaced in tail-like structures trailing "downwind" from the SFRs. Furthermore one

expects the density gradient of the H I to be steeper on the side towards the compressing

wind than on the opposite side.

The gradient in the H I distribution is indeed higher on the eastward edge of the

east side of the ring-arc (Figure 4), which provides some evidence that compression of

the eastward edge of the H I is occurring, at least on the east side of the complex. The

distribution of the H I around the H II complexes (SFRs) B and H, in particular, exactly

fulfills the predictions of this scenario for ram-sweeping by a flow from the east: the densest
- 22 -

H I lies on or slightly west of the optical features,the H I density gradient is steeperto

the eastand shallow,and the H I muchmoreextended,to the west. Theseeffectsare also

present in the complexsouth of knot B: to the east a "prow" of H I wraps steepdensity

gradients closearound a knotty optical feature but tapers more gradually to the west.

However,we note that this sweepingto the west doesnot appear to be true for the knots

in the western arc (particularly K and L), which show a slightly higher density gradient on

their western edges.

Further evidence that ram-sweeping is operating may be indicated by the slightly

asymmetric distribution of the atomic hydrogen in the vicinity of the optical body of the

galaxy. As seen in Figure 4, the gas appears to extend farther to the west of the optical

emission than to the east, which is expected if the H I is being swept to the west.

To examine further the validity of ram-sweeping, Hawarden et al. 1997 have obtained

x-ray images of NGC 5291, first with the Einstein Observatory's Imaging Proportional

Counter (IPC) in 1980 and then with the ROSAT High Resolution Imager (HRI) in

1996. An archival observation of the super-Seyfert galaxy IC 4329A with the ROSAT

Position-Sensitive Proportional Counter (PSPC) (now defunct) is also available. It was

expected that if ram-sweeping was indeed occurring to a significant extent, density

enhancement (and possibly, if the galaxy is moving supersonically, heating) of the ICM

"upstream" of the H I should result in enhanced x-ray emission from just ahead of the H I

being swept. Possible ablation effects were also anticipated.

In fact NGC 5291 is a quite prominent extended x-ray source. Although the resolution

(2'.6) is not sufficient to examine the distribution of the x-ray emission in detail, the Einstein

image (Figure 10) shows a source coincident with the galaxy and possibly extended N-S

along the H II complexes and an apparent "tail" to the west, as might be associated with

ablation by a westward flow. The north-south extent of the x-ray emission is approximately
- 23-

7', somewhatsmaller than the 10'extent of the H I gas. Compressionof the x-ray emission

alongthe easternedgeis alsoevident.

EDITOR: PLACE FIGURE 10 HERE.

The ROSATimages(Hawarden& Chaytor 1997,Hawardenet al. 1997) have confirmed

some, but not all, of this impression. While there certainly exists extended emission which

may be spatially associated with the H II complexes to the north of NGC 5291, several

(variable) sources underly the _'tail" seen in the Einstein image; when these are removed

the tail is reduced. The ROSAT images lie to the west of the H I and H II complexes to the

south of the galaxy.

_.1.2. Large H I Disk Model

Longmore et al. concluded from both the optical and H I velocity field that the

complex of knots and the H I itself were entirely associated with NGC 5291. As noted

above, their interpretation therefore was that of a low luminosity SO galaxy surrounded by

a large (160 kpc) primordial H I disk, similar to the then-unknown Malin 1. Their estimate

of the total mass in the NGC 5291 system, assuming it was a disk in keplerian rotation,

was ;_ 9 x 1011 M®, making it one of the most massive systems then known.

As set out above, this scenario supposes that the outlying star-forming regions in NGC

5291 have been produced by local compression of the H I disk by the ram-sweeping process,

giving rise to instabilities and collapse of large bodies of gas to form the H II complexes

now observed in the optical.

The overall kinematics of the gas in the system, as seen in Figure 8, could be consistent

with a heavily disturbed massive rotating disk centered upon NGC 5291. The eastern
- 24 -

gradients seenin both the H I and x-ray data. as well as the x-ray "tail" to the west are

alsoconsistentwith a ram-sweptdisk system.

The previously unsuspectedring-arc morphologyof the H I complex may argueagainst

the existenceof a large disk however.As discussedin section3.2, above,no atomic hydrogen

was found "filling in" the ring-arc. The associationof the westernmost knots (I-L) is -

alsodifficult to understandif the NGC 5291complex is to be interpreted as a large disk.

Compression and subsequent knot formation along the trailing edge are then difficult to

explain, although it is possible that the western arc traces out a (large!) spiral feature.

There is also evidence that the gas associated with the NGC 5291 system is not

primordial. Metallicity measurements of the gas in the knots, approximately one-third solar

(Duc 1995, Hawarden et al. 1997), is higher than expected for primordial material, and

indicates enrichment from prior star formation. Either the knots formed from pre-enriched

material such as found in the outer parts of actively star-forming spiral galaxies, or there

has been self-enrichment occurring in the vigorously star-forming optical knots. This last

would increase the metallicity of the gas to an extent dependent upon the amount of mixing

in the object (i.e. from stellar winds, etc).

_.1.3. Interaction Model

Although in many ways the NGC 5291 complex does not closely resemble a "classical"

interacting system, many properties of the extensions could be consistent with the scenario

attributing their properties to a tidal origin. The most striking evidence is the optical

morphology of the system. As stated above, the Seashell, with its strongly distorted disk

and sharply-defined, curved southwestern edge is evidence that an interaction could be

of importance, since one is certainly affecting (or has recently affected) this galaxy. Its
- 25 -

projected position closeto NGC 5291makesthe latter the logical candidate to have caused

the disruption, and thereby to have beendisrupted in its turn to produce the outlying

features (though wecannot usetheseto support the identity of NGC 5291asthe disrupter

without prejudging the issueof their origin).

NGC 5291itself may showthe beginningsof a faint optical "tail" and dust lane

extending to the north and slightly west,oppositeto the position of the Seashell,although

it is just as likely that thesefeaturesmay instead be part of a spiral arm. If they are

tidal in origin however(i.e. it is a "tail" and not an "arm"), this type of morphology,

delineatedby tidal armsoppositea companion,with long pa_hy tails and scatteredclumpy

debris resemblingdwarf galaxies,could beconsistwith a high velocity grazing interaction

(Elmegreenet al. 1993).

Most of the features of the H I distribution detailed in these observations could

probably be explained in terms of an interaction. Over three-quarters of the total H I mass

is found in the extensions. The Seashell either is a gas free system or has been stripped

of its atomic hydrogen, and there is more gas associated with the H I Concentration and

with Knot B than with NGC 5291 itself. These characteristics are similar to those seen

in NGC 7252 (Atoms-for-Peace) and NGC 3921, as reported by Hibbard & van Gorkom

1996. They examined a sequence of interacting/merging galaxies, and found that the more

evolved the interaction, the lower the percentage of H I associated with the bodies of the

parent galaxies. They also reported substantial offsets between the H I and the optical

structures of their systems, and found that in the latest stage, essentially all the atomic gas

was located in the tidal extensions.

In addition to the optical and H I morphologies, the one-third solar metallicity of the

gas in the knots is consistent with that expected in material stripped from the outer disk

of a gas-rich system with an active star-forming history (although note the caveat about
- 26 -

self-enrichmentmentionedabove). The H II regions in the tails of the Antennae (NGC

4038/39) also havemetailicities about one-third solar (Mirabel et al. 1994).

The kinematics of the gas (Figures 7 and 8) may also consistent with an

interaction-dominated system. Interactions commonly produce plumes with monotonic

slowly-increasing velocities away from the main bodies, especially if the the material in

the plumes is escaping, so that the outermost features are not returning to the systemic

velocity as occurs in "bound" plumes like those in NGC 7252 (Figure 4 of Hibbard et al.

1994). In an interaction, orbital decay occurs as energy is transferred from the galaxies

to their particles. The particles receive energy and angular momentum from the relative

motion of the passage, which produces the tail-like structures and orbital decay. The tails

produced by these encounters move radially away and fan outwards from the parent systems

and the velocity increases along the tail. At the base, the tail particles are more tightly

bound, turn quickly in their orbits and fall back towards the remnants. The more distant

matter is less tightly bound and falls back more slowly, if at all. This monotonic increase in

velocity along the tail is a prominent feature of the H I structure in the NGC 5291 system.

The relative velocity reaches a maximum, and then as the feature arcs to the NW and

SW, the line-of-sight velocity component decreases as the tangential motions become more

important. The velocity map (Figure 8), for example, quite closely resembles that of the

merger NGC 4676 in Figure 13 of Hibbard & van Gorkom 1996. In NGC 5291 the reducing

velocity differences of the material in the western arc could also perhaps be ascribed to the

slowing of bound material as in NGC 7252, although it is also consistent with the velocity

contours which might be expected if the western arc were an H I feature delineating the

edge of a distorted disk.

We can draw some additional conclusions about the issues to be considered if the

interaction scenario is to be verified. As noted, from the optical image the most obvious
- 27-

candidatefor the partner in this destructive minuet, owing to its contorted shape,is the

Seashell.However,asfirst noted by L79, it is difficult to support this model if the passage

is retrograde. The construction of tidal tails is most pronouncedif the victims rotate in the

samedirection as the passage,and is further enhancedif the latter is roughly coplanar with

the disk of the victim (i.e. the closerthe alignment of the same-signangular momentum

vectorsof the participants, the greatertheir disruption of one another). Sucha prograde

(but not necessarilycoplanar) passageis neededto produce the morphology weobservein

the NGC 5291system. However,the Seashellappearsto be approachingthe observerin

the regionfor which the H I in the systemis receding.Therefore,a progradeorbit requires

a specialorientation for the NGC 5291-Seashellinteraction, and one with a high velocity

passage.It is clearthat careful modelling (alongthe lines of that discussedby Barnes1994

and Hibbard & Mihos, 1995will be required to clarify the possibility of constructing a

successfulscenario.

Alternatively, the SeashellmaYnot be the culprit here. In addition to the orthogonaI

interaction/ring-galaxy hypothesis put forth by L79, M. Balcells (1996, personal

communication)has suggestedthat Knot B is an irregular that hasentered the system at

almost the escapevelocity and is now spiraling into the centerof NGC 5291; perhaps it was

a satellite to the Seashell. Such a model has many resemblances to the relation between

M31, the Milky Way, and the LMC (Lynden-Bell 1994). The dense H I distribution shown

in Figure 3 looks very much like a trail of debris torn from a system dominated by the

Knot B complex. Much of the ring-arc might denote the orbit of the passage, although the

amount of H I involved is considerable, possibly one-half the total mass. The projected

difference in velocity between Knot B and NGC 5291 is 185 km s-_ and the projected

separation is 61 kpc. This would be a bound system if the mass of NGC 5291 were several

times its calculated (minimum) value (section 4.2). However, even one deeply plunging

passage could be extremely damaging if not totally destructive to the "magellanic" system.
- 28-

If, however,this systemhas beenproducedby an interaction betweenNGC 5291and

the Seashell,someof the specificscan be inferred from the velocity field. The relative

velocity betweenNGC 5291and the Seashellis either approximately 450 km s-l(Duc 1995)

or 630 km s-l(L79), and the projected separationis 10.7kpc (L79). Using the lower value,

the massnecessaryto gravitationally bind the Seashelland NGC 5291is then 5 x 1011M®.

The indicative (keplerian) mass for NGC 5291 is 1.5 x 1011 M® (see section 3.2, below),

which is a factor of 3 less than this binding mass. However, there are the usual uncertainties

associated with the unknown orbital phase terms and inclinations to the line of sight which

easily bracket this figure. Furthermore, Barnes (1994) shows that the overall dynamics of

encounters are largely controlled by the extended dark halos of the systems. As part of the

interaction, dark halos transfer angular momentum and energy, imparting spin and raising

broad tidal features. It is this halo interaction that brings about the merger and extracts

luminous tails from galactic disks. In the models considered by Barnes, the ratio of halo to

disk masses is 5:1, which is within the range of corrections to visible masses found by van

Moorsel (1987) in a study of binary galaxies. Given all the uncertainties, we believe that it

is entirely possible that the Seashell and NGC 5291 are bound and merging.

While somewhat suggestive of the debris fields produced in some galaxy encounters,

the optical image (Figure 1) alerts us to the unusual nature of this system. Although

appearance is dependent on both geometry and viewing angle, the complex shoals of objects

(known to be H II regions) to the north and south of the main body in Figure 1 do not

closely resemble the tails and countertails seen in canonical interacting or merging galaxies

such as the "Antennae" NGC 4038/9 and the "Atoms for Peace" galaxy NGC 7252 (e.g.

Hibbard & van Gorkom 1996). Nor, indeed, does this system closely resemble any of the

systems in the atlases of Arp 1966 or Arp & Madore 1987.

The classical interactors produce tails and countertails which are relatively narrow
- 29-

and quite smooth, sometimesstuddedalong their lengths "string-of-pearls" fashionwith a

number of condensations,often H II regions,which generally number a dozenor lessand

arequite inconspicuouscomparedto the continuousstructure. In the NGC 5291complex,

in contrast, there is little continuousstructure discernablebeyondthe visible galaxy. There

are perhaps two faint featuresextending ,,_ 1_5 to the SSE and, reinforced by an inner dust

lane to resemble a weak spiral arm, slightly west of north (Figure 1), but these do not

underlie the main swarms of H II knots. It may also be noted that the H II knots in NGC

5291 are mostly not arranged in a line (except, perhaps, to the south between D and G),

but appear to be spread out laterally (i.e. knots H through M: the western arc) much more

than is usual in the long filamentary arms and tails in the classical interactors. A final

discrepancy is evident in the unusually large number of the H II knots.

The energetics of the gas in the NGC 5291 system imply that a significant fraction of

the gas is unbound (at 20 kpc (72")) unless the galaxy contains a massive halo. The escape

velocity is about 255 km s-1, well below the maximum velocities observed). However, large

velocities and energetics are apparently not rare in the early phases of galaxy mergers.

Similar situations exist for NGC 4676 and especially for Arp 295 (Hibbard & van Gorkom

1996). For these three systems (NGC 5291, NGC 4676, and Aria 295) a mass of order

1012 M® is required to bind the H I. Thus, either substantial amounts of gas escape from

the systems or they possess dark matter. We presume both to be true. Certainly Hibbard

van Gorkom (1996) note the role of escaping gas in the scenario they describe for galaxy

mergers. The existence of large kinetic energies in NGC 5291 is thus neither unusual nor

unexpected, if in fact it is in the early stages of a galaxy merger. Mirabel and colleagues

(Mirabel et al. 1991, Mirabel et al. 1992), find similar situations for the Superantennae

(with a tail 260 kpc in length) and Arp 105; at the tip of a tidal tail, star formation is

occurring. These are objects with masses in excess of the LMC, and which Mirabel and

his associates believe were detached from the progenitor galaxies _ 108 years ago. Star
- 30-

formation is now occurring well after ejection of the tidal debris. Knot B representsan

analogoussituation; we will argue that Knot B is a stable entity (section3.2).

The formation and evolution of dwarf irregular galaxiesfrom tidally removedmaterial

in interacting systemshasbeenpostulatedby Zwicky (1956)and Schweizer(1978). Much

attention has recently beendevoted to clumps in tidal tails, as prominent Ha, H I and

stellar enhancementshave beenshown to exist in theseregions (e.g. Mirabel et al.

1991, Mirabel et al. 1992, Hibbard et al. 1994, Hibbard & van Gorkom 1996). This

discovery of regions of star formation associated with the tidal tails of interacting galaxies

is evidence that gravitational condensation is possible in tidally removed material. Previous

high spatial resolution observations of the H I in tidal tails have shown that the distribution

of gas in these regions is often clumped into organized regions of high density with masses

on the order of 10 _ ME) (Hibbard et al. 1994). These concentrations are very similar

to dwarf irregular galaxies in terms of their sizes, masses, colors, and stellar and gas

distributions. The observed star formation rates are also very similar to those found in

actively star-forming dwarf irregular galaxies.

Numerical modeling simulations have also been performed to test the possibility that

material ejected during a tidal encounter will remain bound, or develop into sub-units

on the scale of dwarf- and even full-sized irregular galaxies (e.g. Barnes & Hernquist

1992, Elmegreen et al. 1993). The models by Barnes & Hernquist (1992) produced strings

of bound subsystems along the unbound tidal tails of two model spirals, passing each

other in a prograde, direct, initially parabolic encounter prior to merging. They find

in their simulations that distinct clumps form in tidal tails, and that these objects are

gravitationally bound and stable against tidal stripping. These clumps form from the stellar

component; the most massive of these clumps are able to capture significant amounts of

gas.
-31 -

Rather similar results were obtained by Elmegreen et al. (1993). They claim that the

interaction will increase the energy of the interstellar medium (ISM) and thereby raise the

Jeans mass. This process erases fluctuations smaller than 108 M®. They show that the

formation of these objects at the ends of tidal tails is a natural consequence of the model,

and that they will continue to exist as distinct objects long after the tails have faded.

Hibbard et al. (1994), amongst others, suggest that the giant H II regions seen near

the ends of the tidal tails in NGC 7252 are examples of such objects; other candidates are

discussed by Mirabel and collaborators (Mirabel et al. 1991, Mirabel et al. 1992, Mirabel

et al. 1994). Indeed. Hibbard & Mihos (1995), in their model of NGC 7252, find that

at least one of these stable clumps will ultimately orbit the remnant as a satellite, with

peri/apocentric distances of 14 and 120 kpc and an orbital period of about 4 Gyr.

It seems clear that interactive processes can and do produce bound systems resembling

dwarf irregulars in this way. Unfortunately, objects like Knot B, or the features in the

Superantennae and Arp 105 discussed by Mirabel et al. (1991, 1992), have gas masses

that are an order of magnitude greater than the total masses of the clumps that appear in

models. It is not clear that current models can account for such large associations forming

in tidal tails. However, they may adequately explain the smaller knots and nebulosities

observed.

Since ram-sweeping is the most obvious explanation for the asymmetry of the atomic

gas and the large x-ray halo and tail, it is possible that we are seeing an interacting system

that is subsequently being ram-swept as it passes through an intracluster medium. However,

neither the ram-swept large disk nor the ram-swept interaction hypothesis alone can easily

explain all of the observed characteristics of this unusual system. Detailed dynamical

modelling is essential if more certain diagnoses are to be obtained.
- 32-

4.2. Analysis of Dwarf Galaxy Candidates in the NGC 5291 System

Regardless of the formation mechanism, it is clear that there are large star-forming

regions associated with the NGC 5291 system. As pointed out by L79, the optical knots

in the NGC 5291 complex resemble dwarf galaxies in size and content. Two conditions

must be met for a concentration of material to remain bound in the outer regions of such _a

complex field. These conditions require that the object (1) remains bound against its own

internal kinetic energy (is self-gravitating), and (2) remains bound against the tidal force of

the parent galaxy. We here examine whether the knots observed in the NGC 5291 complex

can remain bound against these two disruptive influences, as then the likelihood of their

eventual detachment from NGC 5291, to become independent systems, is quite high (see

L79). We note that the following arguments are independent of the process which has given

rise to the overall structure of the complex. (Ram-sweeping in fact causes compression,

providing extra containment and facilitating the production of a bound subsystem; if this

is the initiating process our estimates, below, will be even more conservative.)

To begin to understand the NGC 5291 system it is necessary to develop an estimate

of the total mass present. This may be done in a number of ways, making different

assumptions and therefore arriving at substantially different results. The simplest of these

is to assume, with L79, that the system is a bound rotating disk extending out to the

outermost H I and H II features, and that their velocities are projected orbital velocities.

This results in mass estimates similar to those of L79 (who made this assumption), scaled

for our larger assumed Hubble constant: Mtot "_ 1012 MQ, where we have implicitly assumed

that the galaxy is not far from edgeways-on. This value is large, but not without precedent

in early-type spirals: for example, NGC 5084 (Gottesman & Hawarden 1986) has a mass ,-_

1.5 x 1012 M®, though much less of this is H I than appears to be the case in NGC 5291.

A second approach is to ignore the H I and H II features in the outskirts of the complex,
- 33-

as under the interaction hypothesisof their origin, they may well not be bound to NGC

5291at all. A lower limit to the mass of NGC 5291 may be determined using a different

Keplerian approximation:

rv 2

MK = --_-. (5)

and estimating the orbital velocity as the full width at 20% peak intensity of the H I

velocity profile of the H I in the central optical image, corrected for inclination:

1 AV20

v = (6)

sin i

From Table 3 we have Av20 = 464 km s -1. For the extent of the gas we adopt the

optical major axis extent, 1_1 (NED) 6 and a distance of 58 Mpc, resulting in a linear

diameter of 18.2 kpc. For an inclination of 60 ° (L79) the total mass becomes 1.5 x 10 H M®.

Allowing for a dark halo, we increase this value by a factor of 5, as in the models by Barnes

(1994).

_.12.i. Binding Mass

For an object to maintain gravitational stability, its gravitational potential energy must

equal or exceed its internal kinetic energy. To estimate the binding mass, Mb, necessary

for an object to meet condition (1), we start with the well-known energy equation for two

gravitating point masses:

where a is the semi-major axis of the orbit, and rn is the mass of a "test particle" at a

distance r. Setting a equal to infinity for a parabolic orbit and assuming M >> m, we end

SThe NASA/IPAC Extragalactic Database
up with the classicescapevelocity equation. Rearranging,wefind an expressionfor the

minimum massrequired to bind the system:

r?) 2

Mb= (S)

We approximate the internal kinetic energy by means of the half-width of the H I velocity

profile at the 20 level (! Av20). Assuming an isotropic velocity dispersion: 2

v = v2o). (9)

The velocity profiles for NGC 5291 and the individual knots are shown in Figure 11.

Alternatively, if the H I is in an inclined plane, the v_ correction is equivalent to an

inclination of 35 deg. Our final expression for the binding mass now becomes

2G

As long as the knots are essentially spherical, and we are only considering the dense H I

cores, this is not likely to be much in error.

EDITOR: PLACE FIGURE 11 HERE.

We have evaluated the binding masses for the major knots in the NGC 5291 complex.

To do this, we have estimated the radius of each object from the cores of the H I associated

with each knot as delineated by the high resolution CnB array data. Knots D, J, and L

have cores which are unresolved by the CaB array beam, while F - G is nearly so. We have

therefore used the beamwidth as an upper limit to their diameters. The velocity widths

and H I masses have been determined from the spectra in Figure 11. These spectra were

calculated by summing the flux in each channel of the more sensitive (but lower resolution)

DnC array data cube, within the high density regions ("cores") as delineated by the high

resolution CnB array data; the method makes the exact shapes of the spectra somewhat
- 35 -

uncertain. The velocity widths weremeasuredat 20%of the peakvalue to eliminate someof

the uncertainty due to thesefluctuations. Table 3 lists the velocity widths, radii, resultant

binding masses,and H I massesfor eachobject.

To determinewhether the knots wereself-gravitating, wehavecomparedthe measured

H I massfor eachknot (Table 3) to the binding mass.Valuesrangefrom 0.82for Knot B to

0.02for Knot C. Howeverthis is a conservativetest, which assumesthat there is no other

contributor to the massthan the observedH I. In the caseof knots B and F-G there are

clearly two other components:the stars and the ionized componentin the optically-visible

SFR associatedwith the H I feature, and observedin the radio continuum. Allowing

for these masses, Knot B is self-gravitating, as is region F-G. Knots H, K and the H I

Concentration may be marginally bound as well. The case for the stability of Knot B

against its internal energy is clearly a very strong one. We would have to be underestimating

the mass by more than a factor of 4 before the properties of Knot B are peculiar compared

to a typical irregular galaxy.

4.2.2. Tidal Condition

To evaluate the second condition, we calculated the tidal limit for each dwarf candidate.

The tidal radius is the radius within which material in a knot must lie to remain bound

against the tidal force between the object and the parent galaxy. An object whose actual

radius is smaller than its tidal radius will be stable against tidal disruption.

The tidally limited radius, rT, can be expressed by (von Hoerner 1957):

where rr is the tidal limit of a test particle orbit in the satellite galaxy, M is the mass of

the parent galaxy, m is the mass of the satellite galaxy (both assumed to be point sources),
- 36 -

and Rv is the projected separation between the two galaxies.

Determining the tidal limit requires that the total mass of NGC 5291, the candidate's

separation from it, and the radius of each object be known. The effective tidal radius (rT)

has been calculated for each knot using its measured separation distance from NGC 5291

(listed in Table 3) and the knot's H I mass. The total mass estimate used for NGC 5291 is

7 x 1011M®, which includes the factor of five to allow for a dark halo.

This calculation provides a conservative tidal limit which is correct in detail for a point

source potential, and quite reasonable for this system. We have increased the minimum

mass by a factor of five to allow for the halo mass. Furthermore, the mass of an isothermal,

spherical halo increases directly as Ra. Thus rT is proportional to (Rv) 2/3. As our value for

M cannot be reduced and P_ is underestimated owing to projection effects, our assumed

values for Rv and M should lead to a realistic lower limit to the tidal radius fT. We assume

that the knots, as they are small, are essentially spherically symmetric and any model

dependence on M propagates slowly at the one-third power. Therefore, we believe that the

tidal radius can only be larger than indicated by equation 11.

This tidal limit is compared to each object's radius as measured from the H I data

to determine its tidal stability. As seen in Table 3, most of the high-density cores of the

objects meet this criterion. Knots C, M, and the H I Concentration do not, although for

the H I Concentration, the H I radius (1.9 kpc) just barely exceeds the tidal limit (1.8 kpc).

Candidate components that meet both the binding and tidal criteria are very possibly

irregular galaxies in various stages of evolution. It may be argued that a subset of these

objects become independent irregulars. An understanding of the likelihood of this process of

galaxy formation will allow us to estimate its contribution to the overall dwarf population,

especially in clusters where interactions and ram-stripping are more likely to occur.
- 37-

5. Conclusions and Summary

The high-resolution H I observations presented and discussed above shed considerable

light on the nature of the NGC 5291 system, but do not finally resolve the causes of its

peculiarities. Nevertheless we now have a much clearer picture of the basic parameters.

NGC 5291 is being significantly perturbed by interaction, either with another galaxy, or

with the intracluster medium of AbeU 3574, or both. What remains unclear is the relative

weight of these processes in arriving at the present condition of the system. However we are

at least in the position of being able to describe that condition in some detail. NGC 5291

is attended by veritable shoals of star-forming H II complexes, the brighter specimens of

which are associated with concentrations of H I on our VLA images.

The H I observations establish clearly that a major speculation of L79 was in

several elements correct: at least one (Knot B) and possibly several (H, K, and the H I

Concentration) of the H I/H II features are bound against their own internal energies

and stable against tidal disruption by the nearby galaxy. These objects are therefore

prime candidates for young irregular galaxies produced from stripped galactic material.

An argument particularly may be made for Knot B, which possesses a large young stellar

component (Duc 1995) in addition to its H I mass and performance on the stability criteria.

Knot B appears in every way to resemble an LMC-sized (or larger) "dwarf" irregular galaxy

and would certainly be categorized as such were it to be detached from its parent galaxy,

as appears likely in the next gigayear or so: it is a true, young, galaxy.

We suggest that the other knots may be dwarf irregular galaxies in formative stages

of evolution; Knot B representing the largest and perhaps most highly evolved of these

candidates. An important implication of this work is the verification that genuinely young

galaxies may evolve from components of the debris fields of destructive interactions between

parent systems and both their companions (via tidal effects) and their environments (via
- 38-

ram-sweeping).

Understandingof the processesinvolved in this formation, and hence,for example,the

ageof the new entity, requiressolvingthe puzzleof the dominant processin the NGC 5291

system. We haveattempted to set out the obviousevidencefor the ram-sweepingof a large

disk or of a tidally disrupted system,without selectingeither. This is becauseweconsider

it essentialthat careful modelingof the systemand its processeson both thesescenariosbe

undertaken,if a correct understandingis to be obtained. Suchan understandingis in turn

essentialif the lessonsto be learnedfrom the availability of a young dwarf irregular galaxy

areproperly to be absorbed.

It has beensuggestedthat half or more of the dwarf irregular galaxiesin compact

clusters haveformed from gravitational encountersof the more massivegalaxiesin the

cluster (Hunsbergeret al. 1996). The observations presented herein, along with a growing

body of evidence presented by many other researchers, seriously weaken models of galactic

evolution that attempt to explain the various types of galaxies seen in the universe as the

result of different, independent processes. To date however, too few systems have been

observed to determine if a new class of genuinely young galaxies is truly indicated, or if

instead this formation process is rare in the universe. Further investigations are needed to

establish the extent to which gravitational encounters are involved in the building of dwarf

irregular galaxies.

STG would like to acknowledge stimulating conversations about this topic with Drs.

Marc Balcells and Guillermo Tenorio-Tagle while he was a visiting professor at the Instituto

de Astrofisica de Canarias during 1995-1996 when this work was in its final stages.

Reduction and analysis of the data were made possible by a grant received from the

National Aeronautics and Space Administration Joint Ventures in Research (NASA-JOVE)
- 39-

Project. BKM, STG, and CES would like to acknowledgethe support provided by this

grant, without which this project could not havebeencompleted.

The Digitized Sky Survey image in Figure 4 was obtained using SkyView

(http://skyview.gsfc.nasa.gov/skyview.html). SkyView wasdevelopedand is maintained

under NASA ADP Grant NAS5-32068with P.I. ThomasA. McGlynn under the auspices

of the High Energy AstrophysicsScienceArchive ResearchCenter (HEASARC) at the

GSFC Laboratory for High Energy Astrophysics. The Digitized Sky Survey is basedon

photographic data obtained using The UK Schmidt Telescope,operated by the Royal

ObservatoryEdinburgh, with funding from the UK Scienceand Engineering Research

Council, until 1988June, and thereafter by the Anglo-Australian Observatory. Original

plate material is copyright (c) the Royal ObservatoryEdinburgh and the Anglo-Australian

Observatory. The plates were processedinto the presentcompresseddigital form with

their permission. The Digitized Sky Surveywasproducedat the SpaceTelescopeScience

Institute under US Governmentgrant NAG W-2166.

This researchhasalso made useof the NASA/IPAC Extragalactic Database(NED)

which is operated by the Jet Propulsion Laboratory, California Institute of Technology,

under contract with the National Aeronauticsand SpaceAdministration.
- 40 -
- 41 -

REFERENCES

Abell, G.O. 1958, ApJS, 3, 211

Arp, H.C. 1966, "Atlas of Peculiar Galaxies" (Calif. Inst. of Tech., Pasadena)

Arp, H.C. & Madore, B.F. 1987. "A Catalogue of Southern Peculiar Galaxies and

Associations" (Cambridge Univ. Press, Cambridge)

Balcells, M. I996, private communication

Barnes, J.E. 1994, in The Formation and Evolution of Galaxies, edited by C. Mufioz-Tufion

and F. Sanchez (Cambridge University Press, Cambridge), p. 399

Barnes, J.E., & Hernquist, L. 1992, Nature, 360, 715

Bothun, G.D., Impey, C.D., Malin, D.F. & Mould, J.R. 1987, A J, 94, 23

Clark, B.G. 1980, ApJ, 89, 377

Daly, P.N., Phillipps, S., Disney, M.J., 1987, A&AS, 68, 33

Duc, P.-A. 1995, Ph.D. Dissertation, University of Paris

Elmegreen, B., Kaufmann, M., & Thomasson, M. 1993, ApJ, 412, 90

Gottesman, S.T. & Hawarden, T.G. 1986, MNRAS, 219, 759

Hawarden, T.G. & Chaytor, D.H. 1997, BAAS, (in press)

Hawarden, T.G., Longmore, A.J., Allen, D.A., Gottesman, S.T., & Miller, L. 1997, in

preparation

Hibbard, J. E., & Mihos, J. C. 1995, A J, 100, 140

Hibbard, J. E., & van Gorkom, J. H. 1996, AJ, 111,655
- 42-

Hibbard, J. E., Guhathakurta, P.,van Gorkom, J. H., & Schweizer,F. 1994,AJ, 107,67

Hunsberger,S.D., Charlton, J.C., & Zaritsky, D. 1996, ApJ, (in press)

Hogbom, J.A. 1974, ApJS, 15, 417

Klemola, A.R. 1969, A J, 74, 804

Long-more, A.J., Hawarden, T.G., Cannon, R.D., Allen, D.A., Mebold, U., Goss, W.M., &

Reif, K. 1979, MNRAS, 188, 285 (L79)

Lyden-Bell, D. 1994, in The Formation and Evolution of Galaxies. edited by C.

Mufioz-Tufion and F. Sanchez (Cambridge University Press, Cambridge), p. 85

Lynds, R., & Toomre, A. 1976, ApJ, 209, 382

Mihalas, D., & Binney, J. 1981, in Galactic Astronomy (W.H. Freeman and Company, New

York), p. 489

Mirabel, I.F., Dottori, H., & Lutz, D. 1992, A&A, 256, L19

Mirabel, I.F., Duc, P.-A., & Dottori, H. 1994, in Dwarf Galaxies, ESO Conference No. 49,

edited by G. Meylan and P. Prugniel (European Southern Observatory, Munich), p.

371

Mirabel, I.F., Lutz, D., & Maza, J. 1991, A&A, 243, 367

Pedersen, H., Gammelgaard, P. & Laustsen, S. 1978, The Messenger, 13, 11

Richter, O.-G. 1984, A&AS, 58, 131

Schweizer, F. 1978, in The Structure and Properties of Nearby Galaxies, IAU Symposium

No. 77, edited by E. M. Berkhuijsen and R. Wielebinski (Reidel, Dordrecht), p. 279

Shapley, H. 1936, Harvard Bull., 903, 17
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Sprayberry,D., Impey, C.D., Bothun, G.D. & Irwin, M.J. 1995,AJ, 109,558

Theys, J.C., & Spiegel,E.A. 1976.ApJ, 308,650

Toomre, A., & Toomre,J. 1972,ApJ, 178,623

de Vaucouleurs,G. & de Vaucouleurs,A. 1964, ReferenceCatalog of Bright Galaxies

(University of TexasPress)

deVaucouleurs,G., deVaucouleurs,A., & Corwin, H.G. 1976,SecondReferenceCatalog of

Bright Galaxies(University of TexasPress)

van Moorsel, G.A. 1987,A&A, 176,13

von Hoerner,S. 1957,ApJ, 128,45

Zwicky, F. 1956,Ergebnisseder Exakten Naturwissenschaften,29, 344

This manuscript waspreparedwith the AAS LATEXmacrosv4.0.
- 44 -

Fig. 1.-- B-band Image of the NGC 5291 complex taken with the ESO 3.6m telescope

(Pedersenet al., 1978: reproduced by permission).

Fig. 2.-- Grayscale image of H I integrated intensity from the CnB array data, with 2a

(0.36 x 102o atom cm -_) contour from DnC array data. CnB and DnC array beamsizes

indicated by lower (14" × 13") and upper (50" × 39") ellipses in lower left corner. Crosses

indicate the optical knots identified by L79 (A - H) and the H I features discovered with the

VLA (I- M).

Fig. 3.-- Grayscale image of the H _ integrated intensity from the C+D combined array data.

Contour levels are 1.1 (2a), 5 10, 15, and 20 × 1020 atom cm -2. The beamsize (26" × 15") is

indicated by the ellipse in the lower right corner. Optical and H I knots are indicated with

labeled crosses.

Fig. 4.-- Contours of the H I integrated intensity from the C+D combined array data

superimposed over the digitized optical image from the UK Schmidt IIIaJ Sky Survey plate.

Contour levels are 1.1(2a), 5, 10, 15, and 20 x 1020 atom cm -2. The beamsize (26" × 15") is

indicated by the ellipse in the lower right corner. Optical and H I knots are indicated with

labeled crosses.

Fig. 5.-- Radio continuum contours over optical image. Contour levels correspond to 3, 5,

and 10a (la -- 2.7 × 10 -4 Jy/beam). The beam_size (26" × 15") is indicated by the ellipse in

the lower right corner. Optical and H I knots are indicated with labeled crosses.

Fig. 6.-- Grayscale image of H I integrated intensity from the C+D combined array data.

Outer contour indicates 2a level from DnC array data. Inner contours indicate boundaries

used for determining H I masses of knots.

Fig. 7.-- (a) Individual channel maps from the DnC array data. Contour levels are 2, 5, i0,
- 45 -

15,and 20a. The heliocentric velocity for eachchannelis listed in upper right corner.

Fig. 8.-- Velocity (first moment) map from the C+D combined array data. Isovelocity

contours are 25 km s -t apart and run from 4000 km s-1 to 4725 km s-1.

Fig. 9.-- Velocity dispersion (second moment) map from the C+D combined array data.

Contours are 10, 25, 30, 50, 75, and 100 km s-t.

Fig. 10.-- Einstein X-ray image courtesy T. Hawarden. The very strong source in the

northeast (upper left) of the image is the Seyfert galaxy IC 4329A; the NGC 5291 complex

is the extended source in the center of the frame. North is up; east is left. The grid lines are

2 minutes by 20'.

Fig. 11.-- (a) Velocity profiles for components of NGC 5291 complex. Vertical axis (flux

in Janskys) is drawn to same scale for all six objects. The peak intensity is 0.025 Jy. (b)

Velocity profiles for components of NGC 5291 complex. Vertical axis (flux in Janskys) is

drawn to same scale for all six objects. The peak intensity is 0.0125 Jy; note that the vertical

scale is one-half of that used for (a).
VLA OBSERVING APPLICATION

DEADLINES: 1st of Feb., June., Oct. for next configuration following review

INSTRUCTIONS: Each numbered item must have an entry or N/A

SEND TO: Director NRAO, 520 Edgemont Rd., Charlottesville, VA 22903-24?5

(1) Date Prepared: May 31, 1997

(2) Title of Proposal: The Evolution of Tidal Debris in Interacting Galaxies

A

rcvd:

IFor Grad Students

Only

Who Will Observation.,

(3) AUTHORS INSTITUTION Come To For Ph.D. Anticipated

The VLA? rhesis? Ph.D. Year

B. K. Maiphrus Morehead State University, KY x

S. T. Gottesman University of Florida ?

C. E. Simpson Florida International University, FL x

G. Tenorio-Tagle Institute of Astronomy, Cambridge University, UK ?

C. Munoz-Tunon Instituto de Astrofisica de Canarias, Spain

H.-J. Deeg Instituto de Astrofisica de Canarias, Spain

(4) Related VLA previous proposal number(s):

(5) Contact author

for scheduling:

address:

Caroline E. Simpson

Dept. of Physics

Florida International University

Miami, FL 33199

(6) Telephone: (305) 348-1565

Telex:

Internet: simpsonc@fiu.edu

Other E Mail:

Telefax: (305) 348-3053

(7) ScientificCategory: 0 astrometry,geodesy& techniques,(D solar,0 propagation, (D planetary,(D stellar,(D pulsar,

O ISM, O galactic center, O galactic structure & dynamics (HI), _ normal galaxies, O active galaxies, (_) cosmology

(8) Configurations (one per column)

(A, B, C, D, BnA, CnB, DnC, Any) D

(9) Wavelength(s) 20 cm

(400, 90, 20, 18, 6, 3.5, 2, 1.3, 0.7 cm)

(10) Time requested

(hours) 18.5

(11) Type of observation: _ mapping, C) point source, (_) monitor, C) continuum, O lin poln, C) circ poln, (_) solar, C) VLBI,

(check all that apply) _ spectroscopy, C) mnltichannel continuum, (_) phased array, O pulsar, C) high-time resolution

C) other

(12) ABSTRACT (Do not write outside this space. Please type.)

D configuration 21 cm observations of a sample of interacting galaxies are requested as part of a multiwavelength project to investigate the role of gravitational encounters in the formation of dwarf galaxies. We

intend to identify dwarf galaxy candidates in interacting systems, observe the systems at optical, infrared,

and 21 cm wavelengths to study both their stellar and HI distributions and kinematics, analyze these data to

determine whether the candidates are dwarf galaxies in formation, and perform numerical modeling of these

objects. High sensitivity (D configuration) observations are required to map the extended diffuse HI often

found in the outer regions of these interacting systems. These data will be used to identify candidate tidal

dwarfs and analyze their gravitational and tidal stability; and will provide needed parameters for numerical

simulations, including an investigation into the statistical production of tidal dwarfs. This work could lead

to revisions of current models of galaxy evolution, which has important implications for cosmological models.

NRAO use only
(13)

(14)

(15)

(1{})

Observer present for observations?

Help required: 0 None

Spectroscopy Only:

Transition (HI, OH, etc.)

Rest Frequency (MHz)

Velocity (kin/s)

Observing frequency (MHz)

Correlator mode

IF bandwidth(s) (MHz)

Harming smoothing (y/n)

Number of channels per IF

Frequency Resolution (kHz/channel)

Rms noise (mJy/bm, nat. weight., 1 hr)

Rms noise (K, nat. weight., 1 hr)

Yes O No Data reduction at?

C) Consultation _) Friend (extensive help)

line 1 line 2

HI

1420

637-5061

1417-1396

1A

6.25

N

128

48.828

1.55

0.47

O Home _ AOC or CV (2 weeks notice

line 3 line 4

Number of sources 6 (If more than i0 please attach list. If more than 30 give only selection criteria and LST range(s).)

Band- Largest

Band width angular

(cm) (MHz) line cont. size

(Jy)" (Jy)

D 21 6.25 0.028 2.5'

D 21 6.25 0.139 2.9 I

D 21 6.25 0.192 7.2'

D 21 6.25 0.084 8.7'

D 21 6.25 0.207 5.2'

D 21 6.25 0.008 1.5'

Total Flux Required Time

rms requested l

(mJy/bm) (hours)

1.1 2.5

4.8 0.5

2.7 0.5

1.0 3.5

4.0 0.5

0.5 11.0

Epoch: 1950 _ 2000 O

RA Dec

(1T) NAME hhmm -4- xx.x °

Arp 158 01 22 +33.77

Aria 31 01 48 +21.67

Alp 78 01 56 +18.76

Arp 135 02 37 +38.85

Arp 213 04 03 +69.68

Arp 298 23 00 +08.60

Contig.

"this should be the total flux at the peak of the line

Notes to the table (if any):

(18) Restrictions to elevation (other than hardware limits) or HA range (give reason):

(19) Preferred range of dates for scheduling (give reason):

(20) Dates which axe not acceptable:

(21) Special hardware, software, or operating requirements:

(22) Please attach a self-contained Scientific Justification not in excess of 1000 words. (Preprints or reprints will be IGNORED!)

Please include the full addresses (postal and e-mail) for first-time users or for those that have moved (if not contact author).

When your proposal is scheduled, the contents of the cover sheets become public information (Any supporting pages are for

refereeing only), v3.0 6/94
Scientific Justification

D array observations of a set of interacting galaxies are requested as part of a multiwavelength project to

investigate the role of gravitational encounters in the building of dwarf irregular galaxies. We propose to

study the nature of the interaction and to search for genuinely young dwarf galaxies that may have formed

from breakaway debris. 21 cm observations will be combined with optical and infrared (IR) observations

(provided by the collaboration with the Instituto de Astrofisica de Canarias (IAC)) and numerical simulations

in a comprehensive program.

A new model of the evolution of galaxies is emerging based on HST and other observations and numerical

simulations. Interactions are being shown to play a major role in the evolution of galaxies. Consequences

of these encounters may account for a significant fraction of the dwarf galaxies observed today (Hunsberger

et al. 1996). Numerical modeling has shown that dwarf galaxies are unlikely to form in clusters as density

fluctuations in proto-cluster clouds (Burkert & Silk 1997); some other mechanism may be at work in the

building of these galaxies.

Numerical simulations show that material ejected during a tidal encounter can develop into stable sub-units

on the scale of dwarf irregular and even full-sized irregular galaxies (e.g. Barnes & Hernquist 1992, Elmegreen

et al. 1993). Observations of regions of star formation (e.g. Mirabel et al. 1991, Mirabel et al. 1992) and

high density HI condensations (Hibbard et al. 1994) associated with the tidal tails of interacting galaxies

show that gravitational condensation is possible in tidally removed material. Using a gravitational and tidal

stability analysis, Malphrus et al. 1997 show that a large star-forming region ("Knot B') in NGC 5291's

tidal complex is serf-gravitating and strongly resembles a star-forming dwarf galaxy.

Objects like Knot B have gas masses that are uncomfortably large for many models. What kind of satellite

systems are generated by an interaction? Are tidally stable clumps produced and is it likely that they

will become genuine satellites? What percentage of the existing dwarf galaxies today have resulted from

gravitational encounters?

Proposed Observations

To address these questions, the collaboration is undertaking a multi-wavelength observational program to

be augmented by numerical simulations. We propose to search for small ejecta around a sample of galaxies

which exhibit evidence of gravitational interaction. 21 cm observations will be used to investigate the HI

distribution, dynamics, and kinematics of these systems and their interaction fields. Wide and narrow-band

optical images will be used to identify dwarf galaxy-like companions (Deeg et al. 1997), while imaging in

the near-IR as well as multi fiber spectroscopy will be done to measure velocities and determine the physical

nature, level of excitation, and metallicity of dwarf candidates, and to estimate star formation rates and

ages. Numerical modeling will be done in conjunction with colleagues at the University of Florida and with

Dr. Marc Balcells of the IAC.

D array observations of a subset of the interacting systems being studied by the IAC group are requested

(see figures). These objects represent a variety of Arp types and a range of merging interactions. For

example, Arp 78 and Arp 298 may be representative of early phases of interactions and possile mergers.

The components are well separated showing tidal arms and plumes, faint nebular companions and strong

absorption lanes. In contrast Arp 158 appears to represent a very advanced stage of a merger as the main

body is complex with several centers of emission and a faint tall with knots. The other systems probably lie

between these extremes.

We argue that these six systems represent close passages witnessed at different stages in the merging process.

For Arp 78, Alp 158 and Arp 298, small nebular knots are clearly visible on the Arp and DSS images. The

IAC group (see Deeg et al. 1997) has identified 21 non-stellar objects (NSOs) in the Arp 135 (NGC 1023)

field, while more than 100 are seen in the Arp 78 (NGC 772) field. If these interacting systems form a

temporal sequence, the distribution of ejected matter will vary as a function of the evolutionary stage of the
interaction.Astheinteractionages,muchofthematerialdrawnoutin theearlyphaseswill fallbackinto

the principle galaxy(ies). This may explain the difference between the Arp 135 and Arp 78 fields. We need

to assess the energetics and stability of dwarf candidates, and we will apply the methods developed in our

study of the NGC 5291 system (Maiphrus et al. 1997).

We will see a correlation between the broad distribution of HI and the non-stellar objects. Indeed, STG

(working with data supplied by the IAC collaborators and by John Hibbard) found such a correlation between

HI and the NSOs for NGC 520. Clearly, observations of the atomic hydrogen emission from these systems

is crucial to our understanding of the evolution and energetics of these sytems; these data will constrain the

dynamics and geometry of models.

Observational Parameters

To investigate the possible formation of genuinely young galaxies from tidal debris, we require broad angular

sensitivity to diffuse HI that may be tidally expelled into space by the interaction. Therefore, the CS array

is not of prime interest here as we require sensitivity and not coverage of the UV plane. Based on the results

from the D array data, we will apply for C array time in the future to get improved resolution.

A bandwidth of 6.25 MHz is required to accommodate the large velocity widths (200-500 kin/s) of these

systems and to examine the nearby velocity field for candidate tidal dwarfs. To achieve a velocity resolution

of 10 kin/s, we require a 128 channel spectrometer with a frequency resolution of 48.8 kHz (1 IF, without

on-line Harming smoothing). We have requested enough time to achieve a signal-to-noise of 10:1. The total

time requested includes calibration and move time.

Conclusion

We hope to begin to define the role that collisions play in the building of irregular galaxies. What can

be said about the long term stability of these potential dwarf systems? How do they evolve during the

course of the interaction? The combination of optical and radio observations discussed are designed to

answer such questions. This research will contribute to our understanding of galactic evolution resulting

from gravitational encounters.

Barnes, J.E., & Hernquist, L. 1992, Nature, 360,715

Burkert, A., Silk 1997 UC Berkeley Preprint

Deeg,H.J., Munoz-Tunon, C., Tenorio-Tagle, G., Telles, E., Vilchez, J.M., Rodrignez-Espinosa, J.M., Duc,

P.A., Mirabel, I.F. 1997, "A Catalog of Dwarf Galaxy Candidates Around Interacting Galaxies",

A&A, submitted

Elmegreen, B., Kaufmann, M., & Thomasson, M. 1993, ApJ, 412, 90

Hibbard, J. E., Guhathakurta, P., van Gorkom, J. H., & Schweizer, F. 1994, A J, 107, 67

Hunsberger, S.D., Charlton, J.C., Zaritsky, D. 1996, ApJ462,50

Malphrus, B.K., Simpson, C.E., Gottesman, S.T., & Hawarden, T.H. 1997, A J, submitted

Mirabel, I.F.,Dottori, H.,& Lutz, D. 1992, A&A, 256, L19

Mirabel, I. F., Lutz, D., & Maza, J. 1991, A&A, 243, 367
z_ "'_':_+_ :Y'-_"__ _ '_* -,- : _ I

IUGHT AS_I(_ (B 19_)

fll56--

_ •

t

Fig. 1.-- Arp 31 (left); NGC 7469 = hrp 298 (fight)

_4

"_ o_

e_

Ol 2_4o

4 6 8 tO 12 14

4,.

@,

_. _ _ _ ..,_ .... ".

RIrGHT ASCENSION (B 19_))

Fig. 2.-- NGC 523 = Arp 158
$ I0 12 14

Fig. 3.-- NGC 772 = Arp 78 (left); NGC 1023 = Arp 135 (right)

O4O83O

• i

O0 07 45 _0

RIGHT A,SCE_ ION (B 19_01

Fig. 4.-- Arp 213
The Morehead Radio Telescope: Design and Fabrication of a

Research Instrument for Undergraduate Faculty and

Student Research in Radio Frequency Astrophysics

Benjamin K. Malphrus, Eric Thomas, Michael Combs. Brian Roberts, Bob Ratliff, Brian

Roberts. Chad Pulliam. Jennifer Carter, John Pelfry, Data Preece, and Viju Hullur

Morehead Astrophysical Observatory, Morehead State University, Morehead, ICY 40351

Russell Brengelman, David Cutts, Charles Whidden,

Department of Physical Sciences, Morehead State University, Morehead, KY 40351

Rodney Stanley and William Grizes

Department of Industrial Education and Technology, Morehead State University, Morehead, KY

- 40351

Drew Henderson

Information Technology, Morehead State University, Morehead, KY 40351

Daniel Pucker

ACE Engineering, Morehead, KY 40351

AND

Jeff Kruth

Kruth- Microwave Electronics, Hanover, Maryland

ABSTRACT

Faculty and students of the Departments of Physical Sciences and Industrial Education and

Technology at Morehead State University have designed and assembled the Morehead Radio

Telescope (MRT) to provide a research instrument for undergraduate astronomy and physics

students and an active laboratory for physics, engineering, and computer science undergraduates

and faculty. The instrument functions as a research and educational instrument for undergraduate

students, faculty, and science teachers throughout Kentucky. The goals of the MRT program are

to enhance the curricula in physics, physical science, electronics, and science education programs

by serving to provide: 1.) a research instrument for investigations in astronomy and astrophysics;

2.) an active laboratory in astronomy, physics, electrical engineering, and computer science; and

3.) a research instrument and laboratory for science teacher education and inservice programs. The

telescope incorporates a modular design in which components may be easily removed for use in

laboratory investigations and for student research and design projects. The performance

characteristics of the telescope allow a varied and in-depth scientific program. The sensitivity and

versatility of the telescope design facilitate the investigation of a wide variety of astrophysically

interesting phenomena. The MRT provides hands-on experience in research and instrumentation

technology in a cutting-edge science- one that is in the midst of scientific revolution.
INTRODUCTION

Observational astrophysics is literally in the midst of scientific revolution in that new

instrumentation, namely space platforms and telescopes operating at previously invisible

frequencies (i.e. Gamma ray, X-ray, ultraviolet, infrared, and radio) have been utilized in the

discoveries that have required new paradigms to explain the fundamental structure and function of

cosmic phenomena and of the universe itself. The MRT design provides an msmmaent capable of

supporting scientific research in observational astrophysics at radio frequencies. The design and

fabrication of the basic MRT systems is complete- first light was achieved on October, 12, 1996.

An overview of the MRT Instrumentation, detailed description of major subsystems (antenna, altazimuth drive and control systems, opto-isolator circuitry, receiver systems, and controlling

computer and interface), theoretical performance characteristics, intended scientific programs, and

project significance, is provided herein.

MRT Instrumentation

The basic design of the MRT includes a wire-mesh parabolic reflecting antenna, alt-azimuth

tracking positioner control and drive systems, receiver and signal processing system, a controlling

computer with an interface device, and supporting electronics and hardware (Figure 1.13). The

system is designed around a total power receiver which converts radiation from space coneenUamd

by the antenna system to an electrical signal which is amplified, modified and interpreted. The

MRT system is controlled by a Macintosh Ilsi controlling computer and utilizes a National

instruments Lab NB Interface board, optical isolation system, and robotic drive and control

systems developed by MSU faculty and students. The controlling computer positions the

telescope, instructs it in robotic tracking of cosmic sources, and controls data collection and

storage. The data from a particular experiment is then transferred via ftp to a Sun Sparcstation for

imaging and analysis (Malphrus 1992).

The MRT employs a high gain forty-foot high antenna designed for L-Band operation. A

surplused Army NIKE-Hercules ANS-17 Radar antenna was obtained and modified for radio

astronomy applications. The antenna was selected because of its extremely large aperture,

excellent aperture efficiency (afforded by its innovative offset feed design), and low cost. It

includes L-Band, horn-fed, parabolic reflector and azimuth positioning system. The unmodified

positioning system provided azimuth coverage of 360 degrees at a continuos antenna rotation speed

of approximately six revolutions per minute.

The main purpose of the antenna is to trace the objects in space and collect and concentrate radio

signals from space. These radio signals are then focused by the reflector to a single focal point on

the antenna horn where a waveguide system transmits the wave to a terminus where the front-end

receiver is located. A probe inserted into the waveguide to coax transitions converts the electric

field of the radio wave to an electrical signal via electromagnetic induction. The electrical signal is

then amplified and conditioned by the receiver front-end which then sends the data to the back-end

receiver and controlling computer to be analyzed.
Figure 1.0 Morehead Radio Telescope:

Systems and Subassemblies

Reflecting Surface

Precision Clinomete

Feed Horn

Waveguide System

Focal Feed

Waveguide to-Coax Transition

Front-End Receiver

Astronomer

{to scale)

Dimensions and Motion

Reflecung Surface:

Total Surface Area:

Focal Distance:

Moving Weight:

Total Weight:

Positioner:

Elevation Range:

Azimuth Range:

Slew Rates:

Data Collection:

I I I

!

4_tft x It ft

(13.42 m x 3.35 m)

484 ft2 (50m 2)

3.50 m

1.155 kg

4,527 kg

Automated Az.-alt. system

0° tO 90 °

0° to 360 °

20 rain/360 ° Az.

10 rain/90 ° el.

Automated tracking

and transit modes

Limit Switches

}erstructu_

Elevation Axis

and Bearings

Elevation •Stop B

nterweights

Elevation Control B

Positioning

System

tth Indicator

East End Access Panel

Azimuth Drive System

Translators

Power Supplies

Optical Encoders

Opto-isolator Circuit:

Supporting Electronic
Azimuth and Elevation Drive and Control Systems

Positioning the telescope is accomplished by azimuth and elevation drive and control systems

designed and built by MSU faculty and students and ACE Engineering. The systems utilize a

common controlling computer and interface board and independent electro-mechanical drive-train

and positioning control systems. A block diagram of the azimuth drive and control systems is

provided in Figure 2.0. The azimuth drive system incorporates a traditional translator, stepper

motor, and gearing system that drives a 6-foot diameter bull gear inside a rotating turret to which

the telescope superstructure, antenna, and feed support system (the moving components of the

telescope) are attached. The elevation drive system incorporates a more radical rod and reel type

design. A fixed axle is positioned at the center of gravity of the moving component of the

telescope. The fixed axle is affixed to rotating couplers located on top of a supporting elevation

positioning assembly. Motion in elevation is accomplished by controlling the motion about this

axle with a rod and reel assembly positioned at the base. Cables attached to pick points on the

focal feed support structure are reeled in out around a rod driven by the elevation control assembly.

The elevation control assembly consists of a translator, stepper motor, gearing and coupling

system that controls the rotation of the rod, motion of the cables, and ultimately motion of the

telescope about the elevation axis (Figure 3.0) (Malphrus 1996).

Multiple Use Systems

Macintosh IIsi Controlling Computer:

The Macintosh Controlling Computer has 16 MB of RAM and 1 GB of hard disk memory with a

mathematics co-processor. The Lab-NB which is a low-cost multifunction analog, digital, and

timing UO (Input/Output) board is installed in the computer. It contains a 12-bit successive

approximation A/D converter with eight analog inputs, two 12-bit D/A converter with voltage

outputs, 24 lines of transistor-transistor logic compatible I/O, and three counter/timer channels for

timing I/O. Lab-NB is used with Lab VIEW, a software system that features interactive graphics, a

state-of-the-art user interface, and a powerful graphical programming language. This software is

used to send the iflput pulses to both the azimuth and elevation translators to move the telescope

and analyze the data collected from the optical encoder and clinometer and is also used to collect the

data from receiver system. The signal path from the controlling computer to the drive and

positioning systems is outlined in Figure 4.0.

Inltgaf,.e,.l _o. 

A National Instruments LAB-NB Interface Board is used to interface computer with the

electromechanical hardware. It is a 50 pin board with analog input channels, bi-directional data

lines for ports A; B; & C, control signals, counter inputs; outputs; and gates. It is primarily used to

interface the computer's I/O board with the hard wiring of the telescope's drive, control, and

receiver systems.

Opto-Isolators :

The Opto-Isolators are electronic circuits designed and built by MSU students and faculty and ACE

Engineering. The purpose of the opto-isolators is to isolate high voltage components of the system

from low voltage components of the system. There are two types of opto-isolators - transmitters

which transmit the signals from low voltage circuits and receivers which receive the signals from

high voltage circuits. A system of opto-isolators is incorporated into the drive and control circuitry

for total optical isolation. A schematic diagram of the MRT system as-wired is given in Figure

5.0.
PositionIndication

System

Figure 2.0 MRT Azimuth Control and Drive System
Multiple Systems

C ....

I

i

PositionIndication

systm

I

I

I

Gear

Redncuon

System

Figure 3.0 MRT Elevation Control and Drive System
Fibre 4.0

AZMITH SIGNAL DRIVE

_LOW I WPS

i h'21tgS

P_b_C:_4SWORKS_4RT DWG_T-STRIPS

p.',E¢t ol 4

ELEVATION

FLOW ! .WPS

L|/2I_YJ

_:_h4SWOR K._141tT DWG_T- STR B_

pap Z of 4

SIGNAL DRIVE

RETURN SIGNAL FROM CLINOMETER

FLOW IWP$

'. 1_1_._

P",d_C.LMS WO RKS_I R'F _DWG_T. STR[I_S

_ _t_.ll Ill

_¢J_JD 6

RETURN

!-_Ow I _"PS

_.:m=C '-'_SV_'_RKS_._,IRT DWG,T _TRIP';

SIGNAL FROM ENCODER
R1,R2,R3,R4" 2.21( ohm

RE,RS,RT,RB ,, 220 ohm

Rg,R10,RI1,R12 ,, 220 ohm

SWl

Figure 5.0 Optoisolator circut
L,

Drive and Control Systems:

Azimuth Translator :

The Translator is a self-contained unit incorporating the power circuits and logic elements needed

for bi-directional control of a stepping motor. The azimuth translator was designed and built by

MSU students in cooperation with ACE Engineering. It can be triggered by pulses from an

internal oscillator or from an external pulse source and will drive the motor at rates of 1000 steps

per second. The unit can be operated in ambient temperatures from 0 ° Celsius to +40 ° Celsius. The

Azimuth translator is used to control the azimuth stepper motor and an Elevation translator is used

to control the elevation stepper motor.

SteoDer Motors :

The SLO-SYN stepping motors operate on phase-switched DC motor. The motor shaft advances

200 steps per revolution(1.8 ° per step) when a four-step input sequence (full-step mode) is used

and 400 steps per revolution (0.9 ° per step) when an eight-step input sequence is used. Logic

devices are normally used for switching the speeds. Counter clockwise rotation is obtained by

reversing the order of the switching steps of the clockwise rotation.

Gear Reduction System :

Precision-built parallel shaft speed reducers are specifically designed to provide long, trouble-free

service on heavy duty low speed, high torque applications. They are directly coupled to the stepper

motors in the drive trains of both axes. For the Azimuth system, three speed reducers with ratios

12.5:1, 30:1, 10:1 are coupled back to back to provide a gear reduction of 3750:1. This elaborate

gear reduction system allows the drive train to move the azimuth axis of the telescope at the rate of

one revolution per 23 hours 56 minutes (sidereal day) in the tracking mode and at the rate of one

revolution in 45 minutes in the slew mode. For the Elevation System, one speed reducer with ratio

of 15:1 is incorporated and sufficient to drive the telescope at an appropriate tracking rate and a

slew rate of 10° per minute.

Position Indication Systems:

Azimuth Indication System :

The Azimuth indication system is based on measuring the rotation of an axle in the drive system

with an optical incremental shaft encoder. The Optical incremental shaft encoder is a noncontacting

rotary to digital position feedback device mount on the azimuth drive shaft at the stepper motor

assembly. The internal monolithic electronic module converts the real-time shaft angle, speed and

direction into TrL-compatible outputs. The encoder is used to count the rotations of the stepper

motor shaft. This is basically used as a feedback data to trouble shoot if the count is not equal to

the number of the pulses sent to the stepper motor.

Elevation Indication System :

The Elevation indication system is based on precisely measuring the tilt of the antenna focal plane

with a high-precision biaxial clinometer. The Model 9000 Precision Biaxial Clinometer developed
by Applied Geomechanicsisealow-costbiaxial clinometerfor a wide variety of industrial and

scientific applications(Figure 6.0).A precision electrolytic transducercomprisesthe sensing

element. It has two orthogonal tilt angles (X and Y tilt) and one temperature channel as it's output

channels. The unit can be operated from -10 degrees to 50 degrees Celsius. The clinometer is

mounted on the parabolic reflector of the MRT and one of the orthogonal tilt angle (Y tilt) is used

for our purpose. As the antenna is moved from the local horizon to the zenith, the electrolytic

transducer's voltage is changes accordingly and this value is collected by the computer and the

software converts this value to the degrees to know the exact inclination of the antenna.

MRT Receiver System

I. INTRODUCTION

The MRT receiver system design and fabrication program was a joint effort between MSU

faculty and Kruth-Microwave Electronics Company. The program to design, fabricate and test a

complete radio astronomy receiver system for the reception of signals in the 1420 MHz region was

undertaken in 1993 and completed in 1995. A modular, flexible approach was chosen to permit

simple up-grades as evolving experimentation needs require. Standard mierowave/RF components

were used where possible to reduce development time and to increase reliability. Custom low

noise amplifiers were built to mate with existing antenna feed assemblies. Initial design work was

performed by Malphrus and Cutts at Morehead State University; all additional work was performed

at the Maryland facilities of K-MEC. The system design is comprised of single receiver with

integral low noise amplifier that directly mated to the existing waveguide flange of the MRT

antenna.

II. SYSTEM DESIGN

The overall receiver system design utilizes a low noise, sensitive, stable receiver to convert

the 1420 MI-Iz Hydrogen line frequency to a frequency region suitable for processing by standard

laboratory equipment. A DC voltage derived from an envelope detector is incorporated in the final

stage. In this context, low noise means less than 100 degrees Kelvin, with a goal of 35 degrees or

less. Traditionally; this would have required cryogenic cooling of the fhst stage semiconductor

amplifier. However, advances in GaAs FET technology allowed the fabrication of amplifiera with

35 degree noise temperatures with the device junctions at room temperature (Kruth 1994).

The MRT receiver system incorporates an FET LNA design. The system is comprised of

two major subsystems- the front and back-end receiver systems. The front-end receiver is

mounted at the waveguide terminus mounted on the focal feed support of the MRT superstructure.

A back-end IF processor consisting on one channel of 160-21.4 MHz, and one channel of 21.4-2

MHz conversion is utilized for back-end processing with associated power supplies, monitor

circuitry, and controlling computer. A block diagram of the overall system design is provided in

Figure 7.0.

Major Receiver components include:

LNA assembly, assembled w/Front-end Receiver

Receiver Down converter, 1420 MHz to 160 MHz

WJ IFC-162 160 MHz to 21.4 MHz IF Converter

21.4 MHz to Baseband IF Processor

Fluke 6160 Synthesizer for Microwave Oscillator Control

5 MHz Frequency Standard

Power Supply/Housing for IF Processor

Misc. RF circuitry, cabling, filters, attenuators, etc.
i

i

t.76 (44,7)

1-

:0

Y

T_P V T.E._

;.76

(44,7)

_"-'0.12_ (3,2) 4PLCS

I

2.00 (50,8)

I

_-x cl

I

-"--'--" 2.00 ;n

(_0.8>

i =BvER RED

E _RELJND _'-LACK

3 <-,__UTFUT Z,REEN

-_ " -'_U T--L'- _LUE

T;_ANSDUCER

r-" 0.64 (16..3) /'"

! /

', ,,. --=.-=!N HEADER

J ::_NAL -ND .=_'-'E,:.

-- -- -- C.:NNECTI:N

........ _ _ o_. ....

Figure 6.0 Biaxiai Precision Clinometer Basic Diagram
L--=_ RCVR IPWR/CNT/MNTR_,

I.F.

Cable Bundle

SYSTEM BLOCK DIAGRAM

Power Supply

+ Control

IF PROCESSOR

2 6160

REFERENCE

O

O

Figure 7.0 System Block Diagram
A triple conversion system is used with a first IF of 160 MHz and a bandwidth at the first

IF of 23 MHz. The second conversion translates to a frequency of 21.4 MHz, with a bandwidth

of 1 (2) MHz. The frequency of 21.4 MHz is a standard IF for surveillance radios, and one that a

great variety of filters (both crystal and LC) is available for, so the IF bandwidth can be easily

changed. The final conversion is to baseband, essentially DC-1 MHz. This final conversion is

easily modifiable to allow a flexible choice of final IF before detection. This strategy permits direct

digitization (FFT processing on PC based platforms) as well as experimentation with parallel filter

bank approaches.

The receiver system consists of two major components:

1). Remote receiver front end containing RF circuitry to down convert the 1420 MHz bandit

160 MHz, and

2). The back-end receiver, consisting of monitor circuitry for the convener, additional IF

converter stages, reference oscillator for coherent locking of the receiver front ends, as well as

additional test equipment.

A key feature of this system is that all of the frequency generation components used in the

various conversion stages are phase locked to a common reference frequency. This reference

source consists of a high quality 5 MHz temperature compensated crystal oscillator and associated

buffer amplifiers. Additionally, the 5 MHz source can be derived from a Rubidium or Cesium

beam clock, affording the utmost in stability and accuracy, if such a source becomes available. A

commercial synthesizer drives the phase locked oscillator in the remote receivers, and in turn is

locked to the 5 MHz standard. The use of a common reference frequency scheme such as this

permits the remote receiver to be locked on the receive channel, regardless of external

perturbations, such as weather conditions, seasonal temperature change, etc. This is particularly

desirable in the event that a second receiver is added to the system for the purpose of

interferometric measurements. This design will permit the phase coherent manipulation of the

signals from the second receiver down convener box for interferometry based observations and

experimentation. A more detailed of the circuitry and theory of operation of the front-end and

back-end receivers is provided below.

Front-end Receiver

The front-end receiver consists of the LNA, image reject band-pass filter, mixer, IF preamplifier, IF roofing filter, level set variable attenuator, IF post-amplifier (if required), local

oscillator, and required power supply regulators and control circuitry (Figure 8.0). The front-end

receiver is housed in a box suitable for outdoor mounting at the terminus of the waveguide

mounted on the antenna focal feed support structure (Kruth 1994).

High Electron Mobility Transistors (HEMT) FrET devices are used for the first stage,

followed by GaAs FET gain blocks. The device utilized for the first stage application is the

Nippon Electric Company (NEC) NE32684AF Ultra Low Noise Pseudomorphic Hetero-Junction

FET. This device has a measured noise figure of .3 dB (approximately 30 degrees Kelvin) at room

temperature, with an associated gain of approximately 22 dB at 1400 MHz. This value represents

excellent performance. Care in the amplifier design and fabrication was exercised to preserve these

values. The first stage amplifier achieves .5 dB NF and 18 dB gain using this device. The design

of the input matching stage for this amplifier is critical as any losses from mismatch or attenuation

may directly degrade the noise figure. A simple circuit incorporating the WG-microstrip transition

is utilized, with a single tuned circuit response. With this approach, it is not possible to provide

much filtering, so a filter is added between the following stages.
LNA 1420 MHZ ATTN. ATTN. 160 MHZ 160 MHZ

N

TO ALL

COMPONENTS

SUPPLY

POST_I_

_-0 L.O. SAMPLE

PLO

_) OREFERENCE

INPUT

PHASE LOCK

INDICATOR

SET

ATTN.

Z2-30 VDC

INPUT

Figure 8.0 Front-End Receiver Diagram
This stage is followed by an Avantek packaged gain block pair consisting of a UT02012

and a UT02013 amplifier cascade. This combination provides good gain (20 dB), excellent

intercept point (P-sat = +21 dBm fundamental), and a modest noise figure of 2.5 dB. This

controls the noise figure degradation due to second stage contribution nicely. Due to the high gain

and wideband nature of the first stage amplifier, a front end pre-selection filter is necessary to

block out terrestrial interference. This interference is from diverse sources such as TACAN, radar,

cellular phone harmonics, INMARSAT uplinks and so on. A commercial f'flter was used as this

became available. The bandwidth of this filter is on the order of 150 MHz, centered at 1420 MI-Iz

and the insertion loss is 2 dB. A standard double balanced mixer is used for the fast converter

stage. A standard drive level type is appropriate to this application and the conversion loss is 6 dB.

The 160 MHz IF amplifiers are of conventional design. A coaxial tubular ban@ass f'tlter is

used to establish the bandwidth of the first converter system. Since the desired bandwidth is 2

MHz, a filter of at least 5 x this value must be used to permit future expansion of the experimental

system. The bandwidth of the system is preserved down to the final stage and it is possible to use

wider filters should experimental needs require this. A 20 MHz filter is used to preserve the 20

MHz system bandwidth all the way down to final detection.

The level set attenuator that is included in the design allows manual control of the gain of

the receiver in order to coarsely equalize the gain of the two receivers when used together. Fine

gain control is controlled in the IF processor system. The calculated end to end gain of the frontend is 68 dB. The calculated noise figure is .535 dB based on a .5 dB fast stage and a 2.5 clB

second stage, then an overall noise figure is attainable in the f'u'st stage, then an overall noise figure

of <.4 dB (approximately 40 degrees Kelvin), is attained.

The local oscillator is a phase-locked (PLO) cavity tuned type made by California

Microwave and is a "brick" style oscillator. This oscillator is a fundamental L band cavity using a

low noise bi-polar transistor as the oscillator element. It incorporates a reference multiplier/

harmonic mixer arrangement to permit locking. This oscillator is driven by a synthesizer at

105.0835 MHz and, as the PLO will assume the phase noise and stability character of this

oscillator directly, this reference signal is high quality.

The front-end receiver package is housed in a waterproof aluminum box approximately 12"

x 12" x 12", with all electrical connections made on one face. Thermal insulation and heating

blankets are used to provide a relatively constant temperature environment for the outdoor receiver

unit. An integral power supply is used that operates from 22-30 VDC, and uses well filtered,

regulated DC-DC converters to provide the various voltages required by the system. This permits

a single low voltage feed to the receiver package, for simplicity and safety.

Back-end Receiver

The back-end receiver is comprised of a synthesizer used to generate reference signals for

the down-converter, an IF processor with crystal oscillator for conditioning of the IF signal, a

down-converter power supply, opto-isolation system, and controlling computer and interface

device. A high quality. Fluke synthesizer that can generate the 105 MI-lz range reference signal for

the receiver converters is incorporated into the back-end receiver system. This is an adaptation of

the popular 6160A series that has been modified to use an external 5 MHz standard. The output of

the remote receiver at 160 MHz is shipped by low loss 50 ohm coaxial cable to the indoor rack.

Here the signal is buffed and split. A sample of the 160 MHz "WIDEBAND" If is make available

on the front panel of the control box. The other leg of the power splitter is applied to the 160- 21.4

MHz IF converter system. This system element used is a Watkins-Johnson IFC- 162 IF converter

module, a self contained, system component available from stock at K-MEC. This device uses
21.4 MHz without degradingthe signalto noiseratio. The internal crystal oscillator usedto

convertthe signalwasmodifiedsothatit canbephaselockedto the reference5 MHz oscillator.

Referto Figure9.0 for a schematicdiagramof theback-endreceiver(Kruth 1994).

Additional f'zlteringis thenusedto establishthedesiredfinal bandwidth before detection.

The final conversion brings the 21.4 MHz down the "BASEBAND" by beating against a crystal

controlled oscillator. The frequency of the synthesized oscillator can be changed, along with the

21.4 MHz f'fltermg, to allow different bandwidths at the final detection stage. Buffered sample

ports are available at all pertinent points in the signal path for access to the signal. This is a useful

feature for built-in tests as well as experimentation. The complete receiver system concept has been

shown in block diagram form in Figure 7.0 which provides an overview of the interconneetion of

the various system elements. A regulated high current supply provides 26 VDC nominal for

operating the outdoor receiver package.

A calibrated semiconductor noise source is incorporated into the front end LNA waveguide

port of the receiver package to inject a precise amount of excess noise for calibration purposes, a

precision coupler and altenvator is used to precisely set the injection level of the noise source into

the first amplifier. The coupler was manufactured as part of the amplifier to minimize the impact of

additional insertion loss. In fact, the scheme used did not denigrate the noise temperature,

noticeably.

MRT Operator Program

The computer operator program developed for the MRT is responsible for positioning the telescope

in azimuth and elevation, tracking of cosmic objects as the sky rotates, determining telescope

position in altitude and azimuth via independent feedback loops, and for controlling data coUection

and storage in addition to controlling additional experimental parameters. The initial design of the

controlling program was developed by MSU staff. The program has evolved from its initial de,sign

in order to compensate for operational characteristics of the positioning systems which have

developed as these systems, themselves, have matured. This evolution has been carried out by

students, along with MSU staff, after performing operational tests of the positioning system

components.

The controlling program has been developed with the Labview Virtual Instrumentation software

package, which provides a graphical programming environment "G", with built in accessibility to

the functions of the National Instrument's LAB NB interface card. The graphically intensive

language "G" is ideally suited to the production of programs used in data collection and analysis as

it was initially designed to communicate with interface technologies. Virtual instruments developed

with this package actually mimic hardware components such as spectrum analyzers and

oscilloscopes by conditioning the signal in exactly the same way that the hardware counterpart

would. This package reduces the need for expensive and space-consuming hardware.

The program determines positioning requirements based on the current Universal Time, as well as

the destination coordinates (right ascension and declination) provided by the operator. After

determining the local sidereal time based on this input data, and converting the coordinates of the

object of interest to its current azimuth and altitude, the operator program provides the necessary

control signals to the azimuth and elevation translators via digital I/O ports on the interface card.

The necessary positional accuracy is achieved by monitoring the azimuth encoder and elevation

clinometer. Positional accuracy of 0.10 arcdegrees is achieved via this feedback loop.

The operator program performs transit operational mode by positioning the antenna to the target

location, then monitoring the analog signal from the receiver. Tracking mode additionally

incorporates an algorithm to monitor the deviance of the antenna's position from the desired
I.F. SJ_Jl3

W[OEBA.NO

160 MIiZ OUTPUT

I.FI PROCESSOR

WJ IFC- ] 62

21.4 Mltz

s_u_ j

_ _ >w__,.,_o_

_ -- OUTPUT TO

"_" . MIXER . DETECTOR

2MHZBPF _" ._, _" MHZLPF

Figure 9.0 Intermediate Frequency Processor

Block Diagram
position, with the intention of achieving the aforementioned positional accuracy. It was necessary

for the operator program to evolve based on experiments performed with the mechanical elements

of the positioning system. The number of TTL pulses required to position the telescope in

elevation and azimuth was determined empirically from numerous experiments. These values were

then programmed into the program to automate positioning the telescope. Front-end (user

interface) and back-end (master program diagram) are provided in figures 10.0 ,aa6-4.b,0

respectively. ..

Theoretical Performance Characteristics of the MRT

The minimum detectable flux density, the weakest detectable radio frequency signal from space (A

Stain ), expressed in Janskys (1 Jansky = l0 -26 w m-2 Hz'b may be calculated (Kraus 1986):

where:

AS

rain --- 2K Ks Tsys

E._, Av,at

&Stain = minimum detectable flux density

Ks = receiver constant (-=1)

Tsys = system temperature

k = Boltzman's constant gl.38 x 10"23 J*K -1)

_ap = aperture efficiency (0 <---_ap ._.1) dimensionless

A = aperture area (m 2)

Av = pre-detection bandwidth in [-Iz

At = post detection integration time

Values for the MRT subsystems are obtained from laboratory measurements of the MRT front-end

receiver furnished-by Kruth Microwave Electronics Corporation- K-Met; values for the antenna

system are taken from Army Operational Research Group (AORG)AN-FPS 36 Radar Antenna

Systems Operational Parameters) (AORG 1968). The following values are substituted:

Tsys =67.77 K

Av = 2xl06mHz

Ks = 1

Eap = 0.65

A = 50m2

Assuming a post-detection integration time of one second produces a value of 4.066 x 10 -26 J - 4.06

Janskys.

The total system temperature (Tsys) includes noise contributions due to the waveguide and other

factors is described by (Kraus 1986):
f

mP

]Rk_ P_cena_

Io.oo tl

laz.num_

ID_*na.ont

Iio.oo }!

Ioaa,ra_Az,muml

ILocal Siderea_

[_ncxxlaroutpu_

..._ ......llo.oo '_[.

i

Inza,,a,q

Io.oo I..

Figure 10.0 Operator Program:

Positioning System

Front-end
Altituae

Time Zone

Deairea Azimuth !

Local Sidereal

Figure 11.0 Operator Program:

Positioning System

Back-end
Figure 12.0 Operator Program:

Azimuth Subroutine
I

I

I

036"v + 1.2485"v^2 -

6.6313°v^3 - 0.2949"v^4 +

h8471 *v^5;

Figure 13.0 Operator Program:

Altitude Subroutine
own E]evation_

i

_i Azimuth_

m_

r"- _'_=

,. , _--

Figure 14.0 Operator Program:

Instrument Control Subroutine
Tsys = TA + TLp[ (1/_) -t] + (1/_) TR

where:

Tsys = system temperature

TA = antenna temperature

TLp = physical temperature of waveguide

= transmission efficiency

TR = receiver temperature

Values:

TR = 40.31 ° (from Kruth Microwave Electromcs Corp. K-Me, c)

E = 0.9923 (from MDL Component Book (Waveguide Manufacturer)

For WR-650, Aluminum Loss _ .233 dB/100 at 1421 MH z

Assume 15' of W.G. = .03345 dB loss

Assmne for dipole array efficiency = 50%

Eltieieney of WG = 10(-loss/10) = I0 (-.03345110) = 0.9923

TLp = 290"

TA = 25* (seebelow)

The antenna temperature (T_ was calculated in the following manner (5):

TA = 3K (3K cosmic microwave background radiation)

3K (atmosphere)

2K (scattering from feed support structure)

2K (diffraction spillover to ground)

5K (Ohmic losses)

10K (scattering by inappropriate surface geometry)

25K

Applying these values gives: Tsy s = 25° + 2.242 ° + 40.31 ° --67.73 °

Solving for the minimum detectable cosmic temperature:

ATtain = Ks x Tsys =

AvA t

Recalculated system minimum sensitivity:

0.04787 ° K

ASmin = 2K [ATtain]
ASmin = 2x 1.38x10"23J x 0.04787

(0.65) 50m2

= 4.1357x 10-26 • 4.14Janskys

The spatial resolution (expressed as half-power beamwidth- HPBW) is determined from the

following relationship (Malphrus 1987):

I-IPBW = 58_.Cm)

D (m)

where:

HPBW =

_, =

D =

Half-power beamwidth in degrees

Operating wavelength in meters

Aperture diameter in meters

Calculation of the HPBW of the existing MRT system must be performed in two steps as the

antenna is symmemc about a major and a minor axis.

HPBW of Major Axis:

HPBW = (58) ( 0.211 m)

13.42 (m)

HPBW = 0.91192 °

Repeating the calculation for the minor axis reveals:

HPBW = (58) (0.211 m)

3.355 (m)

HPBW = 3.647 °

Science Programs

The MRT will be employed in a widely varied scientific program. Research programs will range

from investigating single cosmic phenomena to measuring secular variation of radio sources to

mapping structures and areas of sky. The MRT will be utilized in astronomical research programs

in planetary, galactic and extragalactic astronomy, and in SETI Searches. Research programs will

include observing distant galaxies for variability, mapping regions of the Milky Way, spectral

analyses of cosmic phenomena, and the measurement of galactic rotation utilizing measurements of

the Doppler shifts of hydrogen clouds in galactic spiral arms. Astrophysically interesting

phenomena such as quasars, radio galaxies, supernova remnants, giant molecular clouds, HI

regions, cosmic masers, and exotic stars such as neutron stars and possible black holes will be

investigated.
Researchprogramswill include:

*observing distant galaxies for variability

*mapping regions of the Milky Way

*spectral analyses of cosmic phenomena

*galactic rotation and dynamics

J

Astrophysically interesting phenomena will be investigated including:

*quasars

*radio galaxies

*supernova remnants

*giant molecular clouds

*I-IIregions

*coslnic masers

*exotic stars such as neutron stars and black hole candidates

Conclusions and Project Significance

The demilitarization initiatives that the U.S. Government has undertaken has recently prtxtuced a

surplus of high-tech military equipment. Many U.S. scientists have begun to take advantage of the

demilitarization efforts by acquiring and modifying surplus military equipment for use in scientific

research projects. The MRT project is a classic example of the re-utilization of surplus high-tech

equipment for basic science research. The success of the MRT project depends on the validity of

the scientific results produced by the various research initiatives undertaken with the instrument.

The validity of the scientific results is directly related to the performance characteristics of the

instrument. Radio telescopes are generally rated among the largest and most sensitive scientific

instruments ever produced. The scale and sensitivity of instruments is necessitated by the

phenomenally weak radiation that they coflect from space. In point of fact the flux density of even

a moderately strong cosmic source 1420 MHz (the central operating frequency of the MR'F) is on

the order of a few Janskys (Jansky = 10 -26 W/m71Hz). An analogy that radio astronomers use to

describe the phenomenally weak signals detected by these instruments from space is to imagine

converting the electromagnetic radiation into mechanical energy. If one converted all of the

electromagnetic radio frequency radiation from space coflected by all the radio telescopes from all

over the world since the inception of the science in 1932, and converted this energy into

mechanical energy it would roughly be the equivalent kinetic energy contained in a falling

snowflake. If this energy were converted into electric energy it would light a 100 watt light bulb

for almost one second (Malphrus 1996). Because of the inconceivably weak radiation the

performance characteristics of the radio telescope must be conform to research-grade specifications

to perform valid science. The instrument's performance characteristics, specifically antenna gain,

minimum detectable flux density and spatial resolution are critical characteristics that effect the

scientific results of a given research project.
Acknowledgments

Funding for the MRT was provided by the National Science Foundation's Instrument and

Laboratory Improvement program and Morehead State University. Numerous individuals have

been involved in the design and development of the instrument's many subsystems. Individuals

not listed as co-authors that have assisted in the system design and development include Robert

Hayes, Chair of the Department of Industrial Education and Technology, Morehead State

University. Additionally, the following individuals have provided materials and services that have

been vital to the production of the MRT: Steve Leitz and Joe Plank, Physical Plant, Morehead State

University, Dr. Ronald Eaglin, President, and Dr. J.C. Philley, Vice President of Academic

Affairs, Morehead State University.

Literature Cited

Malphrus, Benjamin K., Russell Brengelman, David Cutts, Charles W'hidden. 1992. The

Morehead Radio Telescope: Design and Fabrication of a Research Instrument for Undergraduate

Faculty and Student Research in Radio Frequency Astrophysics. Grant Proposal Submitted to the

National Science Foundation.

Malphrus, Benjamin K., Russell Brengelman, David Cutts, Charles Whidden, Phillip Hitehcock.

1996. The Morehead Radio Telescope Operator's Manual. Morehead State University. Internal

Document.

Kruth, Jeff. 1994. A Receiver System for Radio Astronomy. Kruth Microwave Corporation.

Internal Document.

Army Operationa_ Research Group (AORG) AN-FPS 36 Radar Antenna Systems Operational

Parameters. 1968. U.S. Army Document.

Kraus, J.D. 1986. Radio Astronomy. 2nd edition. Cygnus Quasar Publishers.

Malphms, Benjamin K. and Richard Bradley. 1987. The National Radio Astronomy Observatory

40-Foot Radio Telescope Operators' Manual. Internal NRAO Document.

Malphrus, Benjamin K. 1996. The History of Radio Astronomy and the National Radio Astronomy

Observatory: Evolution Toward Big Science. Krieger Publishers.
I

I@:20 68625: PAGE 82

Xam_ _epe--_eat o_ E_t%am

m_ B28

Morehead State Onlverslt¥

7mlX_- Decembez 1, 1996 - Auqust 31, 1997

.M_: PRISM "Bringing PRISM tO _he Schools"

ii_ $75,000.00 12 33 540 LA00 E417 0512 97 00 SF2 4202

HL_MEtT _: KDE will a=vance $50,000 effective

innedlateiy and $25,000 effective June 1,

1997 and upon compleUlon of the following:

I. Completion of _id-point repor_

O_oII: i. Establish regional network to respond to

local needs for ia_rovinq K-12 mathematics

and science education and for improving use

of inst=uctional tecbnoloqy.

2. Provide on-slte assistance to schools;

develop and implement school needs assessment

and professional development.

3. Evaluate effectiveness of project.

/ _/.A ,-,, /9 U_
Bringing PRISM to the

PROPOSAL COVE_ PAGE

Schools

SUBMITTED BY : _1oreheaa _tace dnivers_t_/

OZ_4a_ za _l on

KENTUCKY DEPARTMEITr OF EDUCATZON R_:GION: _ _'

CONTACT PXlm.SON: 3enjamin K. _alohrus

ORGANIZATION: )4orehead State University PHONZ : [606) 783-2212

ADDRESS : Horehead _tate UniversityT JPO 1325 FA/(: _6063 783-Z130

V,orehead, KY '-035!

TOTAL _RZSM FUNDS REQUESTV_): S

. _.AL MATH .'-USIDS : S

I_MA._L : _.malohrgmorehead-st.edu

79.368

:7,351

PARTNERS :

Signature of Au_hori_ Representative(s)

_onald G. Eaglin. President

_orehead State University

1_I:e

Organization

•._--m_I - A

Offic_ USe on/), -- /

Daue Rec' d

By

,,
EASTERN KENTUCKY

PRISM REGIONAL NETWORK

ABSTRACT

Members of the academic and business communities of Eastern Kentucky. propose to establish the

Eastern Kentucky PRISM Regional Network at Morehead State University (MSU) to serve Region

7. The intent of the regional network is to sustain systemic change in science and matlmmatics

reform begun by the PRISM initiatives. The ultimate goal of these early initiatives as well as the

ctment proposal is to strengthen the quality, of science and mathemaucs instruction in Kentucky K12 classrooms. The various PRISM initiatives have created a cadre of Science Re, ource

Specialists, mathematics specialists and model school teachers throughout Eastern Kentm:ky.

These specialists can provide the basis for a network of mathematics and science teachers in the

region. The current proposal intends to extend gains made by these early initiatives by aligning the

trained specialists closely with other Kentucky. partners m science and mathematics in an integrated

communication network.

The proposed mitiarave intenas to support the PRISM Innovauon Service initiauve in its endeavor

to provide schools in Kenmclcy with comprehensive techmcai assistance to improve and assess

science and mathematics instruction. The proposed network center will link the resources

by the Innovation Service to schools via an integrated communication network of key conmimtors.

In this way, the regional network will assist in organizing resources, increasing the awmtmess

level of each partner's initiatives and by encouraging interaction among the various partner.

The major goal of the proposed project is to establish an integrated communication network whose

purpose is to:

- Coordinate services of various initiatives in the region.

- Provide a mechanism for the delivery, of PRISM and other services, and

- Sustain the State-wide Systemic Initiatives (SSI).

These goals will be accomplished via the development of a comprehensive regional cotmmmmmion

network and the establishment of an associated center to operate and maintain the network services.

The center will work with the regxonai oarmers anti a Regxonal PRISM Advisory Comtmttee

(representatives of partner insutuuons) to implement the network. This project intends to link

partners via an electronic network and through a series of model seminars that utilize the Kenumk'y

Tele-Linking Network (KTLN).

The specific objectivesof the proposed project are to:

J.

2.

3.

4.

.

Establish the Eastern Kentuclcv PRISM Regional Network

Develop and implement an electronic network

Perform a needs assessment

Provide a Seminar Series IKTLN) (4 tele-seminars based on needs assessment)

and lnternet project and participate in a statewide mini-conference

Develop and test an implementarwn plan
MI IOI M DUM OFAGREEMENT j

PROVIDER:

This AGREEMENT is made by

More_ead State University

on mis

(/_Imqf _ & k)

16

and between me Kentucky

day of January

Department of Education and

(hereafter referred to as Provider)

199 6

PERIOD OF CONTRACT:

The period in which me services are to be performed under this contract is from

Sept.ember.lI 1995 to AJm.,,_t"_I. 19_5

TOTAL AMOUNT OF CONTRACT:

The entire amount of this MOA shall not exceed $

42,073.00

('This smouf_ muzt _lUZm tie ToW lludga lis_ on me fweeze =acJe.)

FUNDS:

m GENERAL (01) xx FEDERAL (12) __ AGENCY (13)

ACCOUNT NUMBER:

Services performed are to be charged to the following Account(s):

ACCOUNT NUMBER(S) AMOUNT OR PERCENT

,,_l.7.09-49_t6};z.g6.gg=4pnZ _ $42,073,00

12 33 540 LA00 E417 40 0512 96 0O 4202

PROJECT SCOPE:

The Provider will perform the services herein described: (_.=,,==,== _, ,,,=,.,._.)

/

Dr. Ben Malphrus will serve as Norehead State University's regional

coordinator for PRISM's Science Resource Specia]ists.

CONSIDERATION:

A. FEE

As fee for services hereinbefore set forth, the Department of Education agrees to pay the Provider

by the following method: _Jn._ _.a. m= N ,m.,_ = =,, o=p=m,_ =_E,_.=_ mr_ =,.===a = _,= ==w,=.

CIITy Ioeward il, II0( _lld. )

Provider will bill the KY Department of Education quarterly for_ reimbursement

• of expenses.

I_R_5t996

L .- •

i

BILLING:

Reran all invoices. _lls, or requests for Payment to:

Director. FinancJ=l Semce$.Kentuclo_ Dep4u_el3! o1 Education

,500 IvloroSlrem . 16#_ Floor

Frar#don. ICY 40601

Rev 8/94 Page t of 2
CONSIDERATION:

B. BUDGET

SALARY

FRINGE BENEFITS

CLERICAL/SUPPORT STAFF COSTS

SUPPLIES (Office/Workshops)

SUPPLIES (Books, Pamphlets, etc.)

OTHER RELATED COSTS (Detailed)

$

$

$

$

$

$

$ 42,073.00

of expenses)

TOTAL BUDGET

(see attached breakdown

CANCELLATION CLAUSE:

Either party may cancel the Memorandum of Agreement at any time for cause and may cancel

without cause after thirty (30) clays written notice,

PROVAL:

Ronald 6. Eaglin, PPesident

Rorehead State University

/' Associat-e- C_missio ner

Department _ Education

_'O_pt_'Cg.mmission e_ f_

J J

Director Financi'al Services

Department of Education

Associate Commissioner, Legal Services

Oep_ducatiorl _"

2 -?-2- t

Date

Date

6

Date

Date

Date

Date

Department of Education

Commissioner

Department of Administration

Finance and Administration Cabinet

S.1 j Secretary

Finance and Administration Cabinet

EQual Ol_portunity Employer M/F/O
CAMPUS OBJECTIVES

GRANTAY PROGRAM 1997198

Non-Competitive Proposal

§1. Program Goals and Description: The pnncipai goal of the KSGC is to enhance space-related r_maxr.b and education

in Kentucky, utifizing the excitement of space sciences and missions to help increase interest and pwticipa_on m science,

engineering, and mathematics. The Commonwealth's primary space-science resources consist of faculty and facilities at

consortium member institutions. The KSGC seeks to develop an in_ to increase comm_ cooperation.

collaboration, and support among the present and potential members of the Kenmck'y scace-rclamd nmmuv.h commumty,

and between thispopulationand NASA's R&D programs.

As a component of infrastructure development,cash consortiummember institutioniseligiblefora mm-e.oml_-titivegrant

of up to $I,000 to help theCampus DirectorfacilitateKSGC objectivesthatam identifiedat tim institution(award

contingent upon available funding of the KSGC_. The grant is to be used at the institution to support such activities as

sending faculty members and students to NASA centers to explore resa_h opportunities with NASA, copying anO

dismbuting KSGC and NASA information, and crea[mg ocpormnides for mteracnons on the campus revolving spacesciemists, campus rtscarctmrs, educators, smdcnLs, aria _ public. Cost shanng is encouraged but nix rcquinxt: it may

take the form, for example, of commitment of some of tim Campus Dinaaor's time for the fnn¢_ yQm'. The Campu:

Director will be responsible for identifying relevant objectives at the institution, for developing oc¢ortunities for

involvement of institutional personnel, for administering the grant at the institution, and for providing a Im-iefsummary.

report of expenses and achievements under the grant within thirty days following tim end of the grim tm'm. The fund_

may not be used for equipment or for the direct benefit of the Campus Dirtctor/gnmt administrator;,, lm,amvcr, he or sh(

may be reimbursed for travel for the purpose of developing collaborations and i_.

i

§2. Application for:.

KSGC Campus/Institutional Director (PI):

Consortium lnst/tution and Address:

Phone: (506) 783-2212

FAX: ',C:t05)7I)_-S002

E-raaii: b,ma]phPtPlmreheld-st.edu

Budget: $1,000

KSGC Campus Objectives Grant, AY 97/98 Proposed period:

Benjamn Ralphrus

Rorebead State Untveestt_

Rort_w_d Astr_ys'/caI Laboratory

7101197-6138/98

_ore_O) K7 10351

Request from _ ($1.000 max)

For KSGC campus-objectives/

infiasu'uctute,-building expenses per

conditionsm§l: $ 1,000

Pl:

Fiscal_ D..

Coat Sbarimg (Optional: Campus DiRctor time and/or odin')

8. HlalphPus $ 2,89"/

Supp1les $ 50

KSGC Total $ i,000

Signature

$ 21947

Cost Sharing Total

I I

Benjamin Ma]0hrus, Associate Professor

Typed Name and Title

Porter Oailey, Vice President of Administration and

=iscal _ervices

Total

I

$ 3,947

Datd