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^t r

Spectrophotometry of Two Complete Samples of Flat Radio Spectrum Quasars

1 2

-E. Joseph Wampler., C. Martin Gaskell , William L. Burke

Lick Observatory

Jack A. Baldwin

3

Cerro Tololo Interamerican Observatory

(NASA-CR-175343) SPECTROPHOTOMETRY OF 2 N 84-17077

COMPLETE SAMPLES OF FLAT RADIO SPECTRUM

QUASARS (Lick Observatory, Santa Cruz,

Calif.) 35 p HC A03/!!F AOI CSCL 03A Unclas

G3/89 11617

Submitted to Astrophysical Journal

1. Visiting Astronomer, European Southern Observatory, Garching, Germany

2. Present address: Institute of Astronomy, Cambridge, U.K.

3. Supported by the National Science Foundation

d

J
Abstract

Spectrophotometry of two complete samples of flat-spectrum radio quasars show

that for these objects there is a strong correlation between . the equivalent

width of the CIV X1550 emission liue and, the luminosity of the underlying

continuum. Assuming Friedmann cosmologies, the scatter in this correlation is

a minimum for q 1 1. Altex;natively, luminosity evolution can be invoked to

give compact distributions for q 0 models. A sample of Seyfert galaxies

observed with IUE shows that despite some dispersion the average equivalent

width of CIV X1550 in Seyfert galaxies is independent of the underlying

continuum luminosity. We give new redshifts for 4 quasars.

Subject headings: cosmology galaxies: Seyfert - quaa s•ars• - 

spectroph.otometry

-2-
(1977) .

-3- 

j

I Introduction

Baldwin (1977) suggested that a correlation existed between the strength of

the Ly-a and CIV X1550 emission lines of quasars and the luminosity of the

underlying continuum radiation measured near the wavelength of the CIV line.

Because the sense of the correlation was that the fainter, more difficult to

observe, quasars had the strongest features, the possibility existed that much

of the observed correlation was produced by optical selection effects. In

this study we attempt to reduce, or eliminate, any such effects by observing

all quasars in two complete radio samples. The objects were selected solely

by accura*_a positional agreement between the radio source and a stellar object

on the Palomar Sky Survey (PS) plates. Flat spectrum radio objects were

chosen, partly because the high frequency surveys give very accurate radio

positions and partly because Baldwin (1977) found that the flat radio —^ ctrum

sources gave a slightly better correlation between continuum luminosity .end

line strength than quasars with other radio characteristics. Because strong

emission lines can raise a faint quasar above the threshold for detection on

PSS plates, the strong lined objects are probably overrepresented among the

fainter souces. This is not a serious problem as it is possible to use the

spectrophotometry to identify those objects that are in the sample becuase of 

their strong lines. It is more important to use the radio survey to set upper

limits to the fraction of brighter, weak lined quasars that might exist and

the number of bright, strong lined objects. We emphasize that the new QSO 

samples do not include any of the objects from the original study by Bal
A preliminary paper (Baldwin, Burke, Gaskell and Wampler; 1978) gave early

results after a sample of the flat radio spectrum sources had been observed.

In that paper it was suggested that MgII X2800 might be a useful luminosity

indicator for low redshift quasars. However, as the observations show, a very,

poor correlation between the strength of MgII.X2800 and the continuum at

X2800, the observations of MgII X2800 were discontinued in favor of IUE

observations of a small sample of low redshift quasars from the two radio

surveys„ Also Tarenghi, Vdron and Vdron have communicated to us pre-,

publication measurements of the CIV X1550 strengths and continuum magnitudes

k ^ 

for 23 Seyfert galaxies and low luminosity quasars that have been observed by

IUE. Their, data, together with ours, define boundaries that set upper limits

to the intensity of CIV X1550 as a function of continuum luminosity. The

observations of the complete radio samples and the ratio of BL-Lac objects to

Seyfert galaxies per unit volume of space can be used to limit the number of

faint, weak lined objects that could have been missed in the surveys. 

In section II we give the observations together with a discussion of the

possible observational errors and completeness of the surveys,. The results

are analyxed and discussed in section III and the principal conclusions- are

given in section IV.

II Observational Procedures, Results and Error Analysis

II.1. The data.

The quasars selected for observation were taken from two "complete samples" of 

a flat spectrum radio sources: the NRAO 5-GHz S2 and I survey (Pauliny-Toth

1

et al.; 1972) and the Parkes t 4° survey (Masson and Wall; 1977). In the

a:
w -5-

r

Pauliny-Toth et al. (1972) catalogues there are 21 quasars that have radio

spectral indexes flatter than 0.5 and redshifts above 1.13. For some of the

objects in the catalogue both high and low frequency spectral indexes were

given. When available we used the high frequency index as the criteria for

acceptance of a candidate. We give spectrophotometry here for 20 of these 21

candidates. Photometry for the other, 1211+33, is given by Richstone and

 Schmidt (1980). There are in addition four other candidates that are

acceptable from. their radio properties, Of these, two were later classified

as blank fields by Shaffer (1978), one, 1751+28, is present only as a very

faint image near the limit of the blue PSS and the last, 2337 . 26, is uncertain

and very red (Schmidt, private communication). Neither of these last two,•is

listed in Shaffer (1978). About 25% of the identifications in Shaffer (1978)

differ from those of Pauliny-Toth et al.. (1972). We have observed 16 of the

objects listed by Shaffer (1978). In addition we required candidates to have

tabulated magnitudes brighter than 20 mag. Shaffer's list gives 8 objects that

satisy the magnitude criteria but were not in the Pauliny-Toth et al. (1972)

asample, and which we have therefore not observed. One, 2308+34, has

spectrophotometry by Richstone and Schmidt (1980), another, 007+171, has

spectroscopy by Wills and Wills (1976), in both cases giving redshifts which

should place these objects within our sample. There is only one BSO among the

remaining 6 candidates, the others are neutral or red stellar objects which

are unlikely to be QSOs and only one of which is as bright as 18 mag. However,

the choice of sources for observation was based on the earlier Pauliny-Toth

et al. (1972) catalogue; the newer Shaffer (1978) identifications may be taken

as the amount of uncertainty in the original identification procedure. It is

?,snlikely that many additional candidates would surface from a third pass through

the plate material, so we conclude that the Pauliny-Toth et al. (1972)
.t

-6-

4 '

identifications constitute a complete sample to within about 3-4 QSOs.

Because fit,ding charts for the Pauliny-Toth et al. (1972) sources were not

available when the observing program started Howard French kindly identified

sources for us from computer generated overlays on PSS plates. We are also

indebted to Maarten Schmidt for providing redsh,ifts in advance of publication.

This allowed us to reject low redshift quasars. It is rather remarkable that

among the Pauliny-Toth et al. (1972) candidates there are no BL-Lac type objects.

A few appear in the lists of Shaffer (1978) and one spectacular object, 0215+015,

(Gaske.11; 1982) earns candidate sta.as on the basis of later radio spectroscopy

(Wills and Lynds; 1978) .

The Masson and Wall (1917) list contains 53 candidates with high frequency radio

spectra flatter than 0.5, optical - radio positional agreement tom 6 arc seconds,

estimated magnitudes brighter than 20 mag and right ascension not in the 

7h00m-8h59m range. Of these 25 have z>1.13, two are stars or low redshift

galaxies, 3 have continuous or BL-Lac type spectra, two have noisy spectra but

are probably BL-Lac objects and the remainder have z` 1.13. There are five 

objects in this list that overlap the Pauliny-Toth et al. (1972) catalogue.

Taken together the two lists give us 43 quasars. We have observed all but 1211+33,

for which Richstone and Schmidt (1980) give spectrophotometry, and we have added

0421+01 because Wills and Lynds (1978) list a high frequency spectral index that

places it in our sample.

Spectra of candidate objects were obtained at Lick Observatory using the Image

Dissector Scanner (IDS) system (Miller, Aobinson and Wampler; 1976) attached 

o

to the Shane 3-meter telescope. Typically the resolution of this system is 7A

FZM. Spectra of candidate objects from the Masson and Wall (1977) samples

were also obtained using the CTIO 4-meter telescope equipped with an intensified
-7-

silicon image tube ( SIT) spectrophotometer. In addition a few spectra were

obtained at the AAT using the IDS and photometry of 1705+018 was obtained at

Las Campanas using tire. Sokrectrdgr

•'apla. The SIT spectrophotometer gives a typical

1^114

`

resolution of 10A. Large apertures were used to obtain absolute continuum

• magnitude : ; typically 8 arc seconds at Lick Observatory and 10x60 arc seconds

at CTIO. In order to improve the spectral signal -to-noise for line strength

determination it was the practice at Lick Observatory to also observe each

object with a small aperture in order to reduce the sky background. Spectra

taken with small apert^"res were normalized to the large aperture spectra to

correct for light loss due to differential atmospheric dispersion before

measuring the equivalent widths. The spectrophotometric observations were

calibrated by observing standard stars from the lists of Stone (197 1 ). This

calibration is traceable to the Hayes ( 1970) calibration of bright stars.

Five quasars that were sufficiently bright to observe with International

Ultraviolet Explorer. ( IUE) were chosen from the low redshift portion of the

two surveys. The observing journal for these 5 objects is given in Table 1.

In addition Ulrich et 31. (1980) have published spectrophotometey from extensive

IUE observations of 3C 273, a member of the Masson and Wall ( 1977) list.

These six low redshift members are useful in checking the continuum luminosity,

CIV X1550 line strength correlation for nearby quasars and to anchor the low

redshift position of the Hubble curve. The IUE integration times were very

long and required colla,__b orative observations between VILSPA and Goddard Space

Flight Center. The IUE data were reduced using the standard IUE reduction

package and calibration tables. At the European Southern Observatory (ESO) a

reduction program developed by Massimo Tarenghi removes sharp noise spikes from

the two dimensional geometric and photometric correct images that are available
I

-8-

on the IUE guest observer tapes. The program then extracts the data from'the

two dimensional frame. This procedure results in spectra that have less noise

than the standard IUE reduced spectra which are provided on the guest observer

tape. While the "ESO reduced" spectra were used to determine the continuum

magnitudes and CIV X1550 line strengths a comparison of the ESO and IUE

reductions showed no systematic offsets. We are grateful to Massimo Tarenghi

for giving us his program and explaining its use to us.

Philippe Vdron, Mira Vdron and Massimo Tarenghi (private communication) have

provided us with mean X1550 continuum magnitudes and CIV X1550 equivalent widths

for a large number of Seyfert galaxy spectra that are available in the IUE

archives. These data were reduced using the ESO program mentioned above.

The continuum levels and CIV 1,1550 equivalent widths were determined using an

interactive program developed for the ESO data processing system. We include

the Seyfert galaxy data here, even though the selection of objects was not

controlled by considerations of completeness, as it is instructive to compare

the properties of the Seyfert spectra to those of the quasars.

In Table 2 we give the observational data for the high redshi£t quasars in the

flat spectrum samples and the data for Seyfert galaxies from Vdron, Vdron and

Tarenghi (private communication). For some objects, such as 3C 120, the data

given here, which are based on additional spectra, differ substantially from

earlier published results (Oke and Zimmerman; 1979). In columns 1-3 we give

the name of the object, the source for the identification and its redshift. In

column 4 we give the observed continuum magnitude at the wavelength corresponding

to the redshifted position of ),1550. This continuum magnitude, AB 15501 is

defined as:

AB 1550 - -2.5 log fv1550 - 48.60
where fv1550 is the observed flux at the redshifted position of X1550 in

ergs s-1 cm-2 hz-1 . In column 5 we give the galactic reddening correction

estimated from the HI maps published by Burstein and Heiles (1982). The

reddening correction is not included in the tabulated observed magnitudes,

AB1550 but is included in the plots given in Fig. 4-6. Column 6 gives the

equivalent width of the CIV X1550 line in the rest frame of the quasar. In the

case of 2251+245 a very strong absorption feature blankets the CIV X1550 emission

line. Consequently, the strength of the emission line is very uncertain and we

have not plotted this object in our figures. Column 7 gives the redshift

corrected magnitude, M1550, defined as.

2

M1550 1550 2.5 log (1+z) 43.91 " A1550(l + z)'

This redshift correction is appropriate for Friedmann cosmologies in which

p * qo s 1; A is the reddening correction and a scaling constant was

p; 1550(1 + z)

chosen so that M1550 would be the absolute magnitude if H o

50. Finally 

column 8 we give the telescope ( s) that were used to observe the source.

11.2 Error Analysis.

Rybski ( 1980) .has found that the gain of the IDS systems at McDonald Observatory

i t

LF

are a function of tale exposure time. The effect that he observes could

systematically decrease the magnitudes that we measure for faint objects

compared to the standard stars, which were mostly 10 - 12 mag., by as much.as

0.25 mag. Also Massy (1977) found that the magnitudes determined by Robinson

and Wampler (1973) for galaxies in the cluster Shakhbazian 1 were one to 1.5 mag.

too bright when compared to his photometry. Robinson and Wampler ( 1973)

determined the magnitudes photographically but the calibration was established 

F
by the IDS system. However other comparisons at Lick observatory'of IDS

magnitudes with data from scanners equipped with photomultiplier detectors

showed no large errors„ The present set of data and the availability in the

literature of extensive observations obtained by a number of observers using a

variety of techniques permits a thorough study of our systematic and random

errors. We give here the results of the comparison of our data with that of

others as well as the intercomparison of our observations taken on different

telescopes.

Because quasars vary in brightness, comparisons of observations obtained ott

different dates will be subject to brightness differences as well as

differences caused by photometric errors. But if a large number of objects are

observed the uncorrelated variability only serves' to increase the scatter of the

observational points. Systematic effects, if any, may still be found and limits

" may be placed on the amount of variability in the source or the amplitude of

the observational errors. 

From the Lick Observatory data continuum magnitudes were determined graphically

using eye estimated linear fits to computer plots of the.spectra. The equivalent

widths- of the emission lines were determined by planimetry of the plots.

Allowances were made for absorption lines and Hell X1640, a weak line that is 

blended with the red wing of CIV X1550. For the observations obtained at CTIO 

and the AAT continuum fluxes and the equivalent width of the lines were found 

using an interactive computer program. The internal errors for the northern

and southern hemisphere set of observations were about the same. Excluding

a few obviously variable objects comparison of repeated observations suggests

an internal continuum accuracy of about 10% for the brighter sources that

decreases to about a factor of two uncertainty for the faintest objects. The

IRW

.

-10-
-11--

internal accuracy of the equivalent width measurements to about 30% for the

bright sources and about a factor of two for the faint ones. The uncertainties

in the continuum level are the major component in the uncertainty of determining

the equivalent width of the emission lines for the faint quasars. For the

brighter objects uncertainties in the measurements of the &%allow, extended

wings of the lines contributed substantially to the uncertainties of the

measurements.

An intercomparison between the magnitudes obtained at Lick Observatory and

data from other observers is given in Fig. 1. The agreement between the Lick

and CTIO continuum measurements is in general accordance with the error

estimates. This agreement between the continuum magnitudev in particularly

noteworthy as the CTIO observatiozis were obtained 'with the integrating

television system on the 4-meter telescope. This system might not be subject

to the non-lineaa:ities described by Rybski (1980) which could affect the ?DS 

magnitudes.

The broad band observations shown in Fig. 1 are derived from the PSS, either 

measured or eye estimates. As they include the effect of emission lines 

excluded by the scanners they should give somewhat brighter magnitudes than are

determined by the scanners. Also since the PSS data was obtained about 25 

years before our data were collected the intercomparison of scanner data with 

PSS data will contain the effects of slow quasar variability that would be

only weakly present in measurements which are nearly contemporary with the 

scanner data. Again the agreement is quite good. The observed systematic

shifts can be explained as due to the influence of strong emission lines wh

the scatter of the points is in fact no larger than would be expected from the
.

-;12-

'r

estimates of the observational error. This shows that most of the quasars are

approximately constant in light output even over long periods of time. It is

worth noting, however, that the dispersion of the points about a mean line

tr

increases very rapidly for sources fainter than about magnitude 18.5. This

increased dispersion may be due entirely to the uncertainties in estimating

magnitudes of objects that are near the limit of the PSS plates. However the

possibility remains that, since our quasars have similar redshifts, the

observationally faint sources are also intrinsically faint and the increased

dispersion may be partly caused by increased variability of the fainter quasars,

1 7 arrow band data is available from a number of sources. Oke and Yorycansky

(1982) have published scans of high redshift quasars using the Palomar

Multichannel Spectrometer. While none of the objects observed by them are

included in this study, six of their sources have been observed by Baldwin

y (1977) using the Lick Observatory IDS scanner in his initial investigation of

the CIV X1:550 continuum luminosity effect. Because the earlier data were

obtained using the same techniques and equipment used here a comparison

between the results of the two investigations can yield useful information on

the linearity and accuracy of the IDS system. These data are also shown in

Fig. 1b. While the Baldwin (1977) magnitudes are slightly fainter than those

found by Oke and Korycansky (1982) there is in general very good agreement

between the IDS data and the data obtained using the Palomar Multichannel.

Spectrometer.

For a number of quasars observed in this study Richstone and Schmidt (1980) 

have also published continuum fluxes and CIV X1550 equivalent widths obtained

from observations using the Palomar Multichannel Spectrometer. Richstone et al.

. 
-13-

(1980) has supplemented these measurements with additional data from

observations taken with a TV-type spectrophotometer used at Palomar

Observatory, It is necessary to convert the log f2500 measurements tabulated

by Richstone and Schmidt (1980) and Richstone et al, (1980) to the AB1550

magnitudes we use. We do this by calculating

AB 1500 s

 - 2.5 (log f2500 + a (0,208)) - 48.60

where (2500 and a .are t,r,an from their tables. Using a model they describe

we have also removed the correction for galactic absorption that is included in

their data.

A comparison between these data and ours (see Fig. lb) does not show good

agreement. The scatter seen in Fig. lb for the continuum magnitude comparison

is much than can be explained either from the internal error estimates

or, is v;*,.rw of the lower dispersion seen in comparison with broad band data,

from plausible variations in the sources. The explanation for these

discrepancies is not known.

Comparison between the equivalent width measurements of CIV X1550 is shown in

Fig. 1. 'Satisfactory agreement exists between the CTIO and Lick observations

and between the Lick ID 'S data published by Baldwin (1977) and the multichannel

scanner data "given by Oke and Rorycansky (1982). The equivalent width

measurements published by Young et al. (1982a, b) are systematically smaller

than those found here. However a number of ionic species: He +, 0++, and N++

have weak lines extending to 1640 angstroms. As the high resolution spectra

of Young et al. (1982a, b) do not extend very far into the red it is possible
-14-

that their adopted continuum levels were somewhat too high. Finally we n6te

the scatter in the compari6,1 between the Richstone and Schmidt (1980)

equivalent widths and those given here which is unexplained.

The comparison of our data with that of others leads us to conclude: a) The

IDS systems used at Lick Observatory and at the AAT and the intensified silicon

camera used on the CTIO spectrophotometer are capable of linear photometric

observations of faint objects. b) Most of the bright quasars are reasonably

constant in light output for long periods of time. However there is sufficient

scatter in the data of the faint sources that the possibility remains that

intrinsically faint quasars are more variable than the bright ones.

c) Different observers can produce data with discrepancies that are at least

an order of magnitude larger than the quoted errois. Care should be exercised

when combining data from different observers.

It is much more difficult to assess the errors in determining the continuum

flux and CIV X1550 equivalent width from the IUE observations. There is, as yet

no independent spect'rophotometry for these sources. Fig. 3 shows the IUE spectra

obtained for the five low redshift quasars we observed as part of our luminosity

investigation. We are indebted to R. F. Carswell and E. R. Smith for the IUE

spectrum of PKS 1217+02. As these quasars are near the limiting sensitivity of

IUE, the spectra have substantial shot noise together with an increased chance

for calibration errors. For the Seyfert galaxy data the IUE spectra frequently

had many emission and/or absorption lines which made determination of the

continuum level difficult (Veron, private communication). Thus it is likely

that the errors in the IUE spectrophotometey are at least as great as those

found in the higher redshift sample observed fro m the ground.
III Luminosity - W(CIV) Correlations

In Fig. 4 we give plots of the continuum magnitude at the redshifted position

of CIV X1550 as a function of the logarithm of the equivalent width of CIV in

Y

the rest frame of the quasar. This figure shows that similar correlations

between magnitude and equivalent width of CIV . X1500 exists for quasars at

different redshifts. In this diagram the flat radio spectrum quasars are

x

divided into three groups: 3C 273 together with the six low redshift quasars

observed by IUE, quasars with redshift between 1.1 and 1.9 and quasars with

redshifts between 1.9 and 2.6. For the low redshift objects we give the

absolute magnitudes assuming q o c 1 and Ho = 50. Other cosmologies yield*

5

nearly identical results for the low redshift group. For the two higher

redshift :samples the observed magnitudes are plotted. Because the redshift

s

differences in each of the two high redshift samples are small, differential

cosmological corrections within a group are also small and it is useful to view

i observed magnitudes when assessing observational selection effects. In Fig. 4

all the magnitudes have been corrected for Galactic absorption before the points

were plotted.

We believe that we have observed nearly all the quasars with continuum

magnitudes brighter than 19.5 and redshifts greater than z = 1.13 that are

identified by the two flat spectrum radio surveys. These objects show the

correlation between luminosity and CIV equivalent width. The inclusion of

quasars with continuum magnitudes fainter than 19.5 strengthens the correlation. 

But the radio surveys may be incomplete for objects with continuum magnitudes 

s fainter than 19,5 since for them the presence of strong emission lines increases 

the chance that the object will register well exposed images on the sky survey

plates. If we restrict our attention to the brighter objects we note that

i

t
-16-

even if all of the approximately half dozen BL-Lau objects found in this

survey have high redshift and populate the low equivalent width, low luminosity

part of the diagram, they are insufficiently numerous to produce the rapid

increase in the numbers of faint, weak lined sources proposed by Osmer (1980)

to explain, the absence of bright strong lined sources as a consequence of random

sampling in a population whose space density increases rapidly with decreasing

brightness and line strength. Thus it is clear that these two samples of flat

spectrum radio sources show substantial intrinsic structure in their two

dimensional luminosity / W(CIV) distribution. The existence of such structure

gives an important clue to the nature of the emission line region and can, in

"principle, be used as a "standard candle" for cosmological studies.

In Fig. 5 we plot all our observations on a magnitude - log W(CIV) plot using

Friedmann cosmologies with q o = 0 and q o = 1. The observed magnitudes were

2

corrected by a factor - 2.5 log ( z /1+z) for the q o = 1 case and by

-2.5 log ( z +'k z2)2/,.(1•+z) for the qo = 0 case. If a Friedmann cosmology with

q

0

 = 0 is used the lower redshift quasars are subl:uminous in comparison with

the higher redshift ones. The group of quasars observed with IUE are among

the brightest of the lowest redshift group. If q o is taken to be one, all the

quasars would be approximately comparable in luminosity. There is no evidence

that the spectra of the high and low redshift group of quasars are substantially

different. Baldwin's (1975) comparison of the optical spectra of 3C 273 and

0736+017 showed that it was possible for quasars differeing in luminosity by

nearly three magnitudes to have very similar equivalent wiedths for emission

lines in the 2700 < X < 7000 A region. But the WE observations given here

for 0736+017, although a low weight, suggest that the CIV X1550 line in

0736+017 has a much higher equivalent width than th corresponding line in

3C 273. Thus we find no spectroscopic data to suppoi ne concept that there
-17-

is luminosity evolution of the type required to reconcile our observations with

the predictions of an open Friedmann universe. While, of course, it is possible

that reality may require a totally different cosmological formulation than the

• widely used Friedmann model or that the emission line spectra of quasars are

insensitive to luminosity evolution, we note that these data can be reconciled

with a closed Friedmann universe in which q o = 1.

When the Seyfert galaxy data from the sample of Tarenghi, Vdron and Varon are

added to the magnitude, log W(CIV) plot an interesting interpretation of the

data suggests itself. The Seyfert galaxies all have strong CIV ?,1550 lines

when compared to the quasars. Over half of the quasars from our samples have

^r

e-reiaker CIV X7.550 lines than all but four of the 28 Seyfert galaxies. Fig. 6

^«4

iE Y shows the combined data for the Seyfert galaxies and quasars with the assumptions

"

1

that q = 1 and H = 50 km/sec/Mpc. The Seyfert galaxy data plotted here lie 0 0 

in the same part of the log continuum luminosity/log equivalent width dia

as the data given by Wu et al. (1982). They found a correlation between th

equivalent width of the CIV X1550 emission line and the continuum luminosity

that is not confirmed by the data from Tarenghi, Veron and Veron. These data 

suggest that all Seyfert galaxies have comparable CIV U550 equivalent widths

• 

with a dispersion of approximately a factor of two about a mean value of 100X.

The bright end of the Seyfert distribution joins smoothly with the faint end of 

the quasar relationship. For q o = 1 and Ho = 50 this occurs at an absolute 

n 

continuum magnitude of about - 24. For objects brighter than M1550 - 24 the

average strength of CIV X1550 fails to increase as rapidly as the continuwn 

{ 

magnitude. In fact it is possible to define a lower envelope to the quasar

M /log W(CIV) plot that has a slope corresponding to constant CIV line

1550

^ strength. 

~^ 

4
-18^-

While W1549 ti const. for Seyferts can easily be understood in terms of complete

coverage of the central photoionizing source it is not so easy to understand

why the CIV line for flat radio spectrum quasars show the CIV line luminosl.:y

tending to a constant value and the equivalent width decreasing with increasing

continuum luminosity. The lower equivalent width of quasars can mean any of

t

\

F , the following things:

C.

l;s

a) The observed continuum does not extrapolate to the C ionization edge

(259 A) but instead turns sharply down before then. Observations of very

high redshift quasars do not support this.

b) Some of the continuum we see is beamed towards us and does not contribute

to the photoionization of the broad line clouds. This is believed to be

the case in BI, hacertae objects and the optically violently variable quasars.

c) The average cloud size is smaller than the Stromgren length in quasars,

i.e., the clouds are matter bounded rather- than radiation bounded.

d) The covering factor is lower in quasars than Seyferts.

Further observations are needed to distinguish between these possibilities.

V Conclusions

The addition of new optical data from two complete samples of flat spectrum

radio sources confirms and strengthens the conclusions reached by Baldwin (1977)

and Baldwin et al. (1978) that there is a strong correlation between the strength

of the CIV X1550 lines in quasars and the luminosity of the underlying continuum.

These two new samples are completely independent of the QSO sample which
-19-

originally suggested this correlation. The suggestion by Wu et -al. (1982)

that Seyfert galaxies show a similar correlation, only displaced, is not

confirmed by this data. Instead, these data suggest that the equivalent width

of CIV X1550 in Seyfert galaxies has some real scatter but on the average is

constant and independent of continuum luminosity. Seyfert galaxies appear to

have an upper limit to the equivalent width of their CIV X1550 emission which

is nearly constant for absolute continuum magnitudes that range over 8 magnitudes.

The quasars, however, seem to have an upper limit to the absolute luminosity of

their CIV X1550 lines which range over an additional four magnitudes of

contiuum luminosity. Spectra of all quasars detected in two complete surveys

of flat spectrum radio sources show that contrary to Osmer's (1980) proposal

there are too few faint weak lin?d quasars for this upper limit to be explained

as a sampling effect in a bi-modal power law distribution of line strength and

continuum luminosity. The data fit the predictions of Friedmann cosmologies

with q = 1 without invoking an arbitrary luminosity evolution that is needed O

s for fits to open universes.

The observational errors have been investigated, both by internal checks: and

through the comparison of these data with that of others. These checks

generally show satisfactory agreement. Thus there is strong evidence that the

spectrophotometers used in this investigation are linear and are capable of

accurate photometry. The small scatter found in the comparison of data taken

at different times for the brighter quasars demonstrates that most of these

flat spectrum radio sources are not large amplitude variables even over a 25

year base line.
-20-

r

Acknowledgements

One of us (EJW) thanks the European Southern Observatory for its hospitality

during the reduction of the ME data. We thank M. Tarenghi, P. Veron and

M. P. Veron for providing their Seyfert galaxy data prior to publication. We

are grateful to R. F. Carswell for assisting with the IUE observations. We

are indebted to H. B. French for assistance in the preparation of finding

charts and help with observations. Our,IUE observations were supported by

NASA grant NAS 5-175 and by a grant from the British SERC.
Table

WE Observing Log for Low Redshift Quasars

Date

Name (1981) exp. (min) Camera

0736+017 Dec. 9 410 SWP 15692

Dec. 16 883 SWP 15773

0742+318 April 16 410 LWR 10366

Dec. 18 500 LWR 12177

1103-006 July 22 620 LWR 11111

1146-037 July 18 420 LWR 11084

July 20 650 LWR 11098

Dec. 17 645 LWR 12158

1217+023 July 15 684 SWP 14476 

.i
-22-

ORIGINAL PAGE 19

OF 

pOOR QUALITY Table 2

Magnitudes and CIV %1550 Equivalent Widths 

Name Sample Z AB1550 A1550(1+z) log Wo (CIV) M15505 Telescope4

0103-021 1 2.2011 19.84 0.00 1.94 -24.52 1

0106+013 1,2 2.107 18.42 0.00 1.72 -25.87 1,2"

0112-017 .1 1.366 18.36 0.00 1.48 -25.29 102

0119+247 2 2.025 19.50 0.23 2.04 -24.97 2

0146+056 2 2.35 21.6:., 0.10 2.37 -22.95 2

0149+218 2 1.32 1 20.76 0.29 2.06 -23.13 2

0149+335 2 2.426 18.64 0.20 1.58 -26.06 2

0202+31 2 1.472 18.23 0.28 1.57 -25.81 2

0226-038 1 2.064 17.62 0.00 1.34 -26.65 1

0229+130 2 2.065 19.10 0.00 1.93 -25.17 2

0234+285 2 1.207 18.91 0.41 1.65 -24.96 2

0400+258 2 2.109 21.23 0.40 2.07 -23.47 2

0421+019 .2 2.048 17.59 0.22 1.32 -26.89 2

0454+039 1 1.349 17.05 0.29 1.49 -26.87 2

0457+024 1,2 2.378 19.40 0.20 1.66 -25.27 2 

0458-020 1 2.286 19.532 0.24 1.87 -25.12 2

0504+030 1,2 2.463 18.57 0.30 1.31 -26.25 1 

0736+017 1 0.191 17.95 1.05 1.81: -23.23 5

0742+318 2 0.462 16.34 0.23 1.58 -25.71 5

0748+333 2 1.928 18.04 "0.12 1.71 -26.25 2

0922+005 1 1.720 18.01 0.00 1.40 -25.99 1,2

1004-018 1 1.214 20.8: 0.00 2.2: -22.67 1,2,3

1010+350 2 1.413 20.4 0.00 2.08 -23.30 2

1018+348 2 1.404 19.03 0.00 1.92 -24.66 2

1021-006 1 2.548 19.19 0.00 1.99 -25.38 2

1103-006 1 0.426 16.80 0.24 1.45 -25.11 5

1146-037 1 0.341 18.19 0.00 2.32 -23.07 5

1048+340 2 2.52 1 20.45 0.10 2.13 44.20 2 

11Q•8-00 1 1.982 17.63 0.00 1.54 -26.58 1,2

1217+023 1 0.240 17.06 0.00 2.10 -23.51 5

1226+02 1 0.158 13.4 0.00 1.05 -26.34 5

1351+021 1 1.606 18.50 0.04 1.58 -25.44 1

1356+022 1 1.329 18.82 0.00 1.49 24.78 1,2

1402-012 1 2.522 18.37 0.10 1.68 -26.28 1,2

1449-012 1 1.314 18.15 0.15 1.59 -25.59 2,3

1532 + 017 1 1.42

1

18.652 0.28 1.32: -25.34 1

1602-001 1 1.633 18.132 0.39 1.48 -26.18 1,2

1611+343 2 1.396 18.682 0.00 1.76 -25.01 2

1615+026 1 1.336 17.82 0.34 1.44 -26.14 3

1656+348 2 1.934 18.72 0.00 1.54 -25.45 2

1705+018 1 2.58 19.36 0.28 1.62 -25.50 1,4

2134+004 1,2 1.930 17.39 0.16 1.55 -26.94 2
-23-

Magnitudes and CIV }1550 Equivalent

Widthe

(CIV) M15505 Telescope4

-

ORIGINAL PAGE it

OF POOR QUALITY Table 2

Name Sample3 z AR1550 A1550(1+y) log WO

2223+210 2 1.959 18.15

2243-032 1 1.348 18.102

2251+245 2 2.328 18.58

2254+024 192 2.090 18.10

2320-035 1 1.396 19.15

2328+107 2 1.49 18.83

2332-017 1 1.185 18.302

Mark 335 • 3 0.025 14.56

III Zw 2 3 0.090 16.13

I zw 1 3 0.061 16.54

F 9 3 0.045 13.53

NGC 985 3 0.042 15.25

3C 120 3 0.032 16.75

Akn 120 3 0.033 14.98

,

$7 Mark 79 3 0.022 16.00

NGC 3516 3 0.009 16.38

NGC 3783 3 0.009 16.40

NGC 4051 3 0.002 16.75

Mark 205 3 0.070 16.98

NGC 4593 3 0.008 16.20

Mark 279 3 0.031 15.41

NGC 5548 3 0.017 1548

Mark 506 3 0.043 16.44

30 382.0 3 0.0578 16.49

ESO 141-G55 3 0.037 14.50

Mark 509 3 0.0355 15.13

II Zw 136 3 0.061 15.83

NGC 7213 3 0.0057 17.03

Mark 304 3 0.067 16.35:

MR 2251-178 3 0.068 15.94

NGC 7469 3 0.016 15.41

Mark 9 26 3 0.047 15.39

0.15 1.33 -26.15 2

0.29 1.72 -25.82 2-

0.21 1.0:: -26.07 2

0.11 1.47 -26.30 2 

0.14 1.60 -24.68 2

0.14 1.40 -25.10 2

0.10 1.59 -25.23 2

- 1 .72 -21.31 5 

_ 2.08 -22.46 5

_ 1.56 -21.23 5

- 1.67 -23.60 5

_ 1.77 -21.73 5

_ 2.26 -19.65 5 

1.82 -21.49 5 

_ 1.99 -19.60 5

- 2.05 -17.29 5

_ 2.26 -17.27 5

_ 1.79 -13.66 5

_ 2.06 -21.08 5

5

- 2.02 -17.22

- 1.95 -20.92 5

_ 2.34 -19.56 5 

- 2.16 -20.59 5

- 2.19 -21.17 5^

- 1.83 -22.21 .5

- 2.16 -21.49 5

- 1.66 -21.94 5

- 2.28 -15.65 5^

- 1.83: -21.44 5 

- 2.27 -22.06 5

- 2.01 -19.50 5

- 2.29 -21.83 5

w ._.•.^.--,. _._. .... , w 
-24-

Notes to Table 2:

1. New redshift.

2. The magnitudes measured on different nights are not in agreement. The

object is a suspected variable.'

3. The code for the samples is as follows: 1.'Masson and Wall (1977);

2. Paulins-Toth et al. (1972); 3. Veron, Ve'ron and Tarenghi (private

communication). The data for 1226+02 (30 273) is from Ulrich et al.

(1980)•

4• The code for the telescopes is as follows: 1. CTIO 4-meter; 2. Lick

Observatory 3-meter Shane telescope; 3. Anglo-Australian 4-meter;

4. 2.5-meter at Las Campanas Observatory; 5. International Ultraviolet

Explorer.

5. A Friedmann cosmology with qo = 1 xad Ho = 50 km/sec/Mpc is assumed.
References

Baldwin, J. A. 1975, Ap.J., 201, 26.

Baldwin, J. A. 1977 0 Ap.J., 214, 679.

Baldwin, J. A., Burke, W.'.L., Gaskell, C. M.. and Wampler, E. J. 1578,

Nature, 273, 431.

Burstein, D., and Iseiles, C. 1982, A. J., 8h1, 1165. 

OW

Gaskell, C. M. 1982, Ap. J., 2μ52 0 447.

Hayes, D. S. 1970 0 Ap. J., 159, 165.

Masson; C. R., and 'Wall, J. V. 1977, M.N.R.A.S., 180, 193.

Massy, P. 1977, Pub. A.S.P. 89, 13.

Miller, J. S., Robinson, L. B., and Wampler, E. J. 1976, Adv. Electronics

and Election Phys. (New York: Academic) 408, 693. 

Oke, J. B.., and Zimmerman, B. 1979, Ap. J., 231, L13.

Oke, J. B., and Korycansky, D. G. 1982, Ap. J., 255, 11.

Osmer, P. 1977, Ap. J., 214, 1.

Osmer, 1`. 1980, Ap. J. Suppl., 2, 523.

Pauliny-Toth, I. I. K, :ellerman, K. I., Davis, M. M., Formalont, E. B.,

.and Shaffer, D. B. 1972, A. J., 77, 265.

Richstone, D. E., and Schmidt, M. 1980, Ap. J., 2,35, 361.

Richstone D. 0. Ratnatun a K. and Schaeffer J. 1980 A J. 240 1

> > 8 ► ►

Robinson, L. B., and Wampler, E. J. 1973, Ap. J., 179, L135.

Rybski, P. M. 1980, BAAS, 12, 751.

OV^ 

Shaffer, D. B. 1978, A. J., 83, 209.

wry

1S r^ ^',

Stone, R. P. S. 1974, Ap. J., 193, 135. 

M^ 

-25-
A26-

F

Ulrich, M. H., Boksenberg, A., Bromage, G., Carswell, R., Elvius, A.,

Gabriel, A., Gonhalekar, P. M., Lind, J., Lindegren, L. Longair, M.S.,

Penstron, M.V., Perryman, M. A. C. Pettini, M., Perola, G. C., Rees, M.,

Sciama, D., Snijders, M. A. J., Tanzi, E., Tarenghi, M., and Wilson, R.

1980, M.N.R.A.S., 192, 561.

Wills, D., and Lynds, R. 1978, Ap. J. Suppl., 3N6, 317.

Wills, D., and Wills, B. J., 1978, Ap. J. Suppl., X31, 143.

Wu, C. C., Boggess, A., and Gull, R. 1982, Adv. in Ultraviolet Ast.; Four Years

of IUE Res. (NASA; Conf. Pub. 2238), 160.

Young,'P., Sargent, W. L. W., and Boksenberg, A. 1982a, Ap. J., 2252, 10.

.;Young, P., Sargent, W. L. W., and Boksenberg, A. 1982b, Ap. J. Suppl., 48, 455.
.

-27- 

Figure Captions

Fig. 1: Comparison between magnitudes: a) Lick A31550 and AB1550 obtained by

Baldwin (CTIO) for this study (points) or given by Osmer (1977)

(crosses). b) Comparison between AB 1550 and Richstone et al. (1980)

or Richstone and Schmidt (1980) magnitudes (points) and between

Baldwin (1977) magnitudes and Oke and Korycansky (1982) (crosses). 

c) AB1550 given here and Masson and Wall eye estimate magnitudes from

' the Palomar Sky Survey, d) AB1550 given here and Wills and Lynd

(1978) magnitudes. For quasars with z < 1.6 the blue magnitude was

used; for higher redshift quasars the V magnitude was used.

Fig. 2: Comparison between log W (CIV): Left, Lick values against those

determined by Baldwin (CTIO) for this study (points) or given by

Osmer (1977) (crosses). Right, Lick values against values given by

Richstone et al. (1980) or Richstone and Schmidt (1980) (points) or

Young et al. (1982a, b) (open circles). Comparison between Baldwin 

(1977) Lick values against those given by Oke and Korycansky (1982) 

(crosses).'

Fig. 3: IUE spectra of 5 low redshift quasars taken from the two complete

radio samples. 

Fig . 4: Absolute continuum magnitudes corrected for Galactic absorptions

against the' logarithm of the equivalent width of CIV X1550 measured

in the rest frame of the quasar. Crosses, low redshift quasars

measured with IUE. Points, quasars with 1.1 < z < 1.9. Open 
-28-

circles, quasars with 1.9 ^< z < 2.6.

Fig. 5: Absolute continuum Magnitude plotted against the logarithm of the

rest frame equivalent width of CIV X1550 in the two complete samples.

The symbols are crosses, IUE data for low redshift quasars; points,

+ quasars with 1.1 <z < 1.9; open circles, quasars with 1.9< z< 2.6.

Fig.. 6: Absolute continuum magnitudes against the logarithm of the rest ,frame

equivalent width of CIV 71550 for objects in Table 2 plus the

observations of flat radio spectrum quasars from Baldwin (1977) (open

circles). High redshift members of the two complete radio samples,

r,

filled circles, low redshift members, crosses. Vertical bars,

Seyfert galaxies from Vdron, Vdron and Tarenghi (private communication).

Quasar magnitudes have been corrected for the effects of Galactic

absorption: Seyfert galaxy magnitudes, not. A Friedmann cosmology

with qo = 1, Ho 50 is assumed.

f

4

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r

t ; •

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Authors' Addresses:

E. Joseph Wampler: Lick Observatory, UCSC,

C. Martin Gaskell: Institute of Astronomy,

England

William L. Burke: Lick Observatory, UCSC,

Jack A. Baldwin: CTIO, Casilla 603, La S

Santa Cruz, CA 95064, USA

Madingley Rd., Cambridge, CB3 OHA

Santa Cruz, CA 95064, USA

erena, Chile. 
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