Accepted for publication in The Astronomical Journal, Apr 3,
2007; to appear in the July 2007 issue
U B V R I Photometry of Stellar Structures throughout the Disk
of the Barred Galaxy NGC 3367
J. Antonio Garćıa-Barreto, Héctor Hernández-Toledo, Edmundo Moreno-Dı́az
Instituto de Astronomı́a, Universidad Nacional Autónoma de México, Apartado Postal
70-264, México D.F. 04510 México
Tula Bernal-Maŕın and A. Lućıa Villarreal-Castillo
Facultad de Ciencias, Universidad Nacional Autónoma de México, México D.F. 04510
México
ABSTRACT
We report new detailed surface U,B, V, R, and I photometry of 81 stellar
structures in the disk of the barred galaxy NGC 3367. The images show many
different structures indicating that star formation is going on in the most part of
the disk. NGC 3367 is known to have a very high concentration of molecular gas
distribution in the central regions of the galaxy and bipolar synchrotron emission
from the nucleus with two lobes (at 6 kpc) forming a triple structure similar
to a radio galaxy. We have determined the U,B, V, R, and I magnitudes and
U−B ,B−V , U−V , and V −I colors for the central region (nucleus), a region
which includes supernovae 2003 AA, and 79 star associations throughout NGC
3367. Estimation of ages of star associations is very difficult due to several factors,
among them: filling factor, metallicity, spatial distribution of each structure and
the fact that we estimated the magnitudes with a circular aperture of 16 pixels
in diameter, equivalent to 6′′.8 ∼ 1.4 kpc. However, if the colors derived for
NGC 3367 were similar to the colors expected of star clusters with theoretical
evolutionary star tracks developed for the LMC and had a similar metallicity,
NGC 3367 show 51% of the observed structures with age type SWB I (few tens
of Myrs), with seven sources outside the bright surface brightness visible disk of
NGC 3367.
Subject headings: galaxies: stellar structures — galaxies: individual (NGC 3367)
— galaxies: starburst—galaxies: photometry
1. Introduction
It is a continuous topic of study how a galaxy evolves with time (Larson 1977; van der Kruit
1989; Pfenniger 2000). Integrated photometry of star clusters and star associations in a
galaxy can provide fundamental insight on the star-formation history (Bica et al., 1996).
U,B, V colors of galaxies depend mainly on their history of star formation (Searle, Sargent & Bagnuolo
1973; Larson & Tinsley 1978). The fact that morphologically peculiar galaxies show bluer
http://arxiv.org/abs/0704.1450v1
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U −B colors in the two color diagram suggests that galaxies with peculiar appearance have
experienced anomalous star formation histories characterized by recent burst. Models with
recent bursts of star formation (SFR) predict colors that in general lie off the normal relation
for models with monotonically decreasing SFR (Larson & Tinsley 1978), for example, a very
recent strong burst results in an excessively blue U−B for a given B−V (Larson & Tinsley
1978). Integrated photometry of star clusters and star associations in a galaxy would provide
fundamental insight on the star-formation history (Bica et al., 1996).
NGC 3367, the disk galaxy with a stellar bar of our study, is noteworthy because of
observational characteristics, some of them are: 1) it shows a bipolar synchrotron outflow
from the nucleus with a compact unresolved source with deconvolved diameter less than 65
pc, and two large lobes straddling the nucleus with a total, projected extent on the sky,
from the north-east to the south-west lobe of about 12 kpc (an image like a radio galaxy,
but from, a nearby late disk galaxy); only the south-west lobe shows polarized emission,
suggesting that this lobe is out of the plane of the disk and is closer to the observer than
the other lobe (Garćıa-Barreto et al. 1998; Garćıa-Barreto, Franco & Rudnick 2002); 2)
the axis of the ejected outflow is highly inclined with respect to the axis of rotation of the
disk of the galaxy (Garćıa-Barreto et al. 1998; Garćıa-Barreto, Franco & Rudnick 2002);
3) there is a lot of molecular gas mostly concentrated in the central 9′′ with an unresolved
source with M(H2) ∼ 5.9× 10
8 M⊙; this molecular mass suggests an optical extinction value
Av(l) ∼ 75 magnitudes toward the nucleus (Garćıa-Barreto et al. 2005) (as it has been
detected through its CO(J=1-0) emission with the OVRO mm Array1); its total molecular
(H2) mass within 11.4 kpc diameter is M(H2) ∼ 2.6× 10
9 M⊙ (Garćıa-Barreto et al. 2005);
4) it shows a bright southwest optical structure (resembling a “bow shock”) with a collection
of Hα knots at a galactocentric radius of about 10 kpc from the nucleus (Sandage 1961;
Garćıa-Barreto, Franco & Carrillo 1996a; Garćıa-Barreto et al. 1996b), 5) it has crooked
arms in its northwest side, and 6) it seems to be isolated with no similar-diameter galaxy in
its proximity; NGC 3367 lies, behind the Leo group of galaxies, at a distance of 43.6 Mpc,
with a closest companion lying at a projected distance of ≈ 563 kpc or 18 optical diameters
away (Garćıa-Barreto, Carrillo & Vera-Villamizar 2003).
NGC 3367 is an SBc(s) barred spiral galaxy with a stellar bar structure of diame-
ter ≈ 32′′ ∼ 6.7 kpc oriented at a position angle (P.A.) ≈ 65 − −70◦. The disk is in-
clined with respect to the plane of the sky at ∼ 30◦ (Garćıa-Barreto & Rosado 2001).
NGC3367 has an X ray luminosity much larger than any normal spiral galaxy (Gioia et al.
1990; Stocke et al. 1991; Fabbiano, Kim & Trinchieri 1992). Its radio continuum emission
at a 4′′.5 angular resolution shows weak radio continuum emission extended throughout
the disk (Garćıa-Barreto et al. 1998). From Fabry Perot observations of the Hα emis-
sion it is deduced that the kinematic major axis lies projected on the disk at a P.A.
of 51◦ (Garćıa-Barreto & Rosado 2001). Its optical spectrum shows moderately broad
Hα+[NII] lines with FWHM∼ 650 km s−1, but its emission of Hβ is stronger than its
emission of [OIII]λ5007Å and there is weak emission of He II λ4686Å suggesting the ex-
istence of WR stars (Véron-Cetty & Véron 1986; Véron, Gonçalves & Véron-Cetty 1997;
Ho, Filippenko & Sargent 1997). NGC 3367 has been clasiffied as an HII nucleus (from
the optical line ratios; see (Ho et al., 1997a) and normal content of atomic hydrogen with
1The Owens Valley Radio Observatory millimeter array is operated by Caltech and it is supported by the
National Science Foundation grant AST 99-81546
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MHI ∼ 7× 10
9 M⊙ (Huchtmeier & Seiradakis 1985). Table 1 lists relevant information for
NGC 3367 coming from the literature.
Previous U,B, V, I phometry of NGC 3367 has been obtained for the whole galaxy
with magnitudes reported in RC3 (de Vaucouleurs et al., 1993) and compiled in the NASA
Extragalactic Data Base (NED)2 as listed in Table 1; previously reported colors are as follows:
U − B = −0.16, B − V = 0.55, B − I = 1.45. Larson & Tinsley (1978) have discussed
different factors that would affect the U,B, V colors, among them are reddening (galactic
and intrinsic), gaseous emission lines and nonthermal emission, chemical composition and
initial mass function (IMF). The color B − V of NGC 3367 agrees with the color expected
from a late type disk galaxy (Allen 1976; Larson & Tinsley 1978); however the U −B color
of NGC 3367 certainly lie above the mean value of normal disk galaxies and the position in
the U−B vs B−V (Larson & Tinsley 1978) is more in agreement with the statistical colors
of galaxies from the Arp Atlas of peculiar galaxies 3. These colors of NGC 3367 suggest that
this late type barred galaxy is currently having many regions with recent star formation.
Although galactic reddening is a major source of uncertainity in the U,B, V colors, for
this galaxy it is not a major concern given its lalitude, b = +58◦. We report our magnitude
estimates for the different structures corrected for Galactic extinction. Gaseous emission
lines, different chemical composition and different initial mass function may contribute to
the uncertainities of the expected colors (Larson & Tinsley 1978).
This paper reports new U,B, V, R, I photometry of 81 individual structures throughout
NGC 3367 using the 84 cm optical telescope in San Pedro Mártir, Baja California, México
(Richter, et al. 2005). For the data reduction and analysis we used the IRAF4 task phot
with an aperture radius of 8 pixels (3′′.41 ∼ 715 pc). The existence of a close connection
between violent galactic dynamical phenomena is consistent with theoretical expectations
that high velocity collisions and shock fronts should be effective in compressing gas to high
densities and triggering rapid star formation. Section 2 reports the observations, §3 reports
the results and §4 gives the discussion and finally §5 describes the conclusions.
2. Observations and Data Reduction
The observations were carried out using the 84 cm optical telescope at the Observatorio
Astronómico Nacional at San Pedro Mártir, Baja California, México on 2005, March 8 and
9. We used a CCD camera Site3 with a 1024×1024 pixels; each pixel size is equivalent to
2NED is operated by the Jet Propulsion Laboratory, California Institute of Technology under contract
with the National Aeronautics and Space Administration.
3As a comparison the U − B and B − V of an early type (elliptical) galaxy are U − B ≥ +0.55, and
B − V ≥ +0.80 (Larson & Tinsley 1978).
4The IRAF package is written and supported by the IRAF programming group at the National Optical
Astronomy Observatories (NOAO) in Tucson, Arizona. NOAO is operated by the Association of Universities
for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation
(NSF).
– 4 –
0′′.426 and we did not use any binning. Attached to the camera was a filter box. A journal of
the photometric observations is given in Table 2. Column (1) give a characteristic; columns
(2)-(6) give the filters; rows indicate the data for each column, seeing, central wavelength
and total width of the filter used, and the number of frames times the integration time (in
seconds) of each of the images (M67 and NGC 3367) in each filter. Images were debiased,
trimmed, and flat-fielded using standard IRAF procedures. First, the bias level of the CCD
was subtracted from all exposures. A run of 10 bias images was obtained per night, and
these were combined into a single bias frame which was then applied to the object frames.
The images were flat-fielded using sky flats taken in each filter at the beginning and at the
end of each night. In the case of estimating the magnitudes for the structures throughout
the disk in NGC 3367, we have made careful analysis utilizing different IRAF tasks, in
particular, qphot and phot using different aperture diameters for bright stars in the field of
NGC 3367 in order to estimate the uncertainities in the final magnitudes at different filters
before estimating the final magnitudes reported for the different structures in NGC 3367.
The magnitudes reported here for the structures within NGC 3367 were estimated using an
aperture radius of 8 pixels (∼ 3′′.4 ∼ 715 pc).
Photometric calibration was achieved by nightly observations of standard stars of known
magnitudes from the “Dipper Asterism” M67 star cluster (Guilliland et al., 1991; Chevalier & Ilovaisky
1991). A total of 9 standard stars with a color interval −0.1 ≤ (B − V ) ≤ 1.4 and a similar
range in (V − I) were observed. The main extinction coefficients in B, V , R and I as well
as the color terms were calculated according to the following equations (Larsen 1999):
U − u0 = αU + βU(u− b)0
B − b0 = αB + βB(b− v)0
V − v0 = αV + βV (b− v)0
R− r0 = αR + βR(v − r)0
I − i0 = αI + βI(v − r)0
where B, V , R and I will be the estimated magnitudes, b, v, r and i are the instrumental
(and airmass-corrected) magnitudes. α and β are the transformation coefficients for each
filter.
In a first iteration, a constant value associated with the sky background was subtracted
from the images by using an interactive procedure that allows the user to select regions
on the frame free of galaxies and bright stars. Notice that uncertainities in determining
the sky background may be the dominant source of uncertainities in the estimation of the
magnitudes, color and surface brightness profiles.
The most energetic cosmic-ray events were automatically masked using the IRAF task
cosmicrays and field stars outside the bright visible disk of NGC 3367 were removed using
the IRAF task imedit when necessary. Within the galaxy itself, care was taken to identify
superposed stars. A final step in the basic reduction involved registration of all available
frames for each galaxy and in each filter to within ±0.1 pixel. This step was performed
by measuring centroids for foreground stars on the images and then performing geometric
transformations using IRAF tasks geomap and geotran.
All final images were convolved with a two dimensional gaussian function in such a way
as to have a similar final resolution equivalent to the largest one given by the V filter seeing,
that is, full width at half maximum, fwhm∼ 2′′.2.
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2.1. Uncertainities in the Photometry
2.1.1. As a result of the Method
An estimation of the uncertainities in our photometry involves two parts: 1) The pro-
cedures to obtain instrumental magnitudes and 2) the uncertainty when such instrumental
magnitudes are transformed to a standard system. For 1), notice that the magnitudes pro-
duced at the output of the IRAF routines qphot and phot differ from each other as a result
of different methods used in those procedures. Since we also have applied extinction correc-
tions to the instrumental magnitudes in this step, our estimation of the uncertainities are
mainly concerned with these corrections and the estimation of the airmass. After a least
square fitting, the associated uncertainities to the slope for each principal extinction coeffi-
cient are; δ(kU) ∼ 0.038, δ(kB) ∼ 0.038, δ(kV ) ∼ 0.035, δ(kR) ∼ 0.025 and δ(kI) ∼ 0.025.
An additional uncertainity δ(airmass) ∼ 0.005 from the airmass routines in IRAF was also
considered.
For 2), the zero point and first order color terms are the most important to consider.
After transforming to the standard system, by adopting our best-fit coefficients, the formal
uncertainities from the assumed relations for α were 0.05, 0.05, 0.04, 0.04 and 0.04 in U ,
B, V , R and I and 0.04, 0.03, 0.03 and 0.04 for β. To estimate the total uncertainity
in each band, it is necessary to use the transformation equations and then propagate the
errors. Total typical uncertainties are 0.1, 0.1, 0.1, 0.09 and 0.1 in U , B, V , R and I bands,
respectively.
The estimated total magnitudes in this work were compared against other estimations
reported in the literature. This has been done for the standard stars and for NGC 3367 in
common with other works.
2.1.2. Standard Stars as calibrators
Our estimated CCD magnitudes for the nine stars in M67 are listed in Table 3 along with
magnitudes and cross reference identification numbers reported in the literature (Guilliland et al.,
1991; Chevalier & Ilovaisky 1991). A plot of our CCD estimated magnitudes versus those
reported by Guilliland et al., (1991) and Chevalier & Ilovaisky (1991) are shown in Figure
1 with no significant deviations, a continuous line with slope 1 is also plotted. These results
suggest, a σ ∼ 0.12, as the typical magnitude uncertainity. This is in agreement with our
prior uncertainity estimations.
– 6 –
Fig. 1.— Comparison between our estimated magnitudes and those from Gilliland et al.
(1991) [U , B, V and R bands] and Chevalier & Ilovaisky (1991) [I band] for 9 stars in
common taken as standards
3. Results
3.1. Total Magnitudes and Colors
In this study, we have estimated total magnitudes for U,B, V, R, I computed from differ-
ent circular apertures chosen interactively to assure that they are large enough to contain the
whole galaxy and still small enough to limit the uncertainities due to bad estimation of the
flux from the background and any field stars. Finally we chose an aperture with a diameter of
140′′ equivalent to 2′.33; this is slightly larger than the 2′.02 major diameter as given in NED.
There is, however, a foreground star within the disk of NGC 3367 which we did not remove
before estimating the global magnitudes and colors for NGC 3367. The star is object 82 in
Tables 7 and 9 and it lies about 29′′ to the north-west of the nucleus; we did not attempt to
remove it because it is surrounded with emission from stellar structures in the disk and thus
it makes it difficult to estimate the intensity level to replace the star with; star ID 82 turns
out to be a weak star with magnitudes U ∼ 17.9 B ∼ 17.9 V ∼ 17.4 R ∼ 16.9 I ∼ 16.2.
Total magnitudes from NGC 3367 were estimated in each band by using the phot routines
in IRAF. Our final estimated magnitudes for NGC 3367 were corrected for Galactic ex-
tinction (but not for intrinsic extinction); they are U = 11.70 ± 0.1, B = 11.91 ± 0.1,
V = 11.52 ± 0.1, R = 11.05 ± 0.1, and I = 10.43 ± 0.1. The colors of NGC 3367 are
U −B = −0.21, B − V = 0.39, B − I = 1.48.
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Since the aperture to estimate the magnitudes for the stellar structures throughout
NGC 3367 must be small in order to include only star associations or small structures, it
was decided to use an aperture with radius 8 pixels equivalent to 3′′.41 ∼ 715 pc and use
IRAF task phot. One compared the estimated magnitudes, with an aperture of 8 pixels,
for the bright stars in the field south west of NGC 3367 with those listed in Table 5 (with
aperture radius of 26 pixels). The magnitude differences vary according to the star and
the filter. For star ID 86 the difference in empirical magnitudes are ∆U(8 − 26) = 0.07,
∆B(8 − 26) = 0.09, ∆V (8 − 26) = 0.10, ∆R(8 − 26) = 0.09, and ∆I(8 − 26) = 0.17; while
for star ID 91 the differences in magnitudes are ∆U(8 − 26) = 0.06, ∆B(8 − 26) = 0.08,
∆V (8 − 26) = 0.11, ∆R(8 − 26) = 0.10, and ∆I(8 − 26) = 0.18, fair is to say that the
magnitudes with aperture radius of 8 pixels have been corrected for Galactic extinction.
Magnitudes differences for each filter for both stars are similar indicating indeed that using
a smaller aperture radius gives an artificial weaker object by the amount given in each filter
but the differences are within the values for the uncertainities of our method. The estimated
magnitudes for the different structures throughout NGC 3367 (stellar associations) can be
taken as reliable and are listed in Table 6. Table 7 lists the estimated magnitudes for the
bright stars and a background galaxy in the field of NGC 3367. Table 8 lists the different
colors U −B, B− V and V − I for the stellar structures throughout NGC 3367, while table
9 lists the colors of the stars and the small galaxy in the field of NGC 3367. See Tables 6
for comments on individual objects.
Our estimated magnitudes for the whole galaxy in U , B, V and I bands and those
reported in the RC3 Catalogue (de Vaucouleurs et al., 1993) are in good agreement. The
Galactic extinction towards NGC 3367 in the different filters are: AU = 0.15, AB = 0.12,
AV = 0.09, AR = 0.08, and AI = 0.05 (Schlegel, Finbeiner & Davis 1998).
3.2. UBV RI Photometry of Star Associations and structures
It is a complicated problem to carry out photometry of stellar structures located within
the disk of a galaxy, partly because of the strongly varying background, and partly because
the structures are not perfect point sources (in other words, there must be a varying filling
factor) nor circles (as it was our aperture). For disk galaxies, the colors U − B, B − V ,
V − I are closely related to spectral type and show that there exist remarkable differences in
stellar content (Searle, Sargent & Bagnuolo 1973). The colors of structures in a given galaxy
are most certainly affected by internal reddening and chemical enrichment. In a particular
galaxy, as in our study, the colors of different structures would indicate the contributions
of the component stars in star clusters, very young star clusters embedded in HII region or
compact HII regions, stellar associations without gas, associations embedded in HII regions
and star clusters and associations with traces of emission [e.g. (Bica et al., 1996)].
It was decided in our photometric study of structures in NGC 3367 to estimate the
color magnitudes of different structures using IRAF task phot with an aperture with radius
8 pixels (3′′.4) which translates, in NGC 3367, to a radius with linear scale of 715 pc. No
aperture correction were applied to our estimated magnitudes of the different structures.
The photometry of all structures was obtained with the IRAF task phot which takes an area
of the sky, well off the extention of the disk of the galaxy in study, as a background to be
– 8 –
compared with.
In order to have an estimation of how good were our derived magnitudes for the stellar
structures throughout NGC 3367, we first estimated the magnitudes of bright field stars to
the south west of NGC 3367 (objets ID’s 85 and 90 in Table 7) utilizing two IRAF tasks,
qphot, and phot; each of these stars is relatively isolated and thus we could use apertures
with different radii in order to estimate their magnitudes in the five filters. Table 4 gives
our estimated magnitudes for the different filters for two bright stars in the south west
of the field of NGC 3367 utilizing IRAF task qphot using an aperture radius of 23 pixels,
equivalent to 9′′.80, and a width of ring (in order to estimate the brightness of the sky) of
pixels, equivalent to width of ring of 2′′.13. Additionally IRAF task phot was used with
three different circular apertures, one with a radius of 20 pixels, equivalent to 8′′.52, other
with radius 23 pixels, equivalent to 9′′.80 and another one with 26 pixels, equivalent to
11′′.08. The estimated magnitudes for the five filters, U , B, V , R, and I, are listed in Table
5. The largest uncertainity observed in Table 5 using three different apertures amounts to
∼ 0.05 mag in U , B, V , and R and it is ∼ 0.13 mag in I for both stars. Comparison
between estimated magnitudes using IRAF tasks qphot and phot for these field stars may
be estimated comparing the results listed in Tables 4 and 5. The difference amounts in the
worst case to 0.12 mag indicating that indeed IRAF task phot obtains a brighter value in
each filter with the largest aperture; however the difference in magnitudes using different
apertures with IRAF task phot is at worst ∼ 0.03 in the I filter between using an aperture’s
radius of 20 pixels and an aperture’s radius of 26 pixels.
The structures were chosen from the images in the I and U filters by eye at several loca-
tions of the disk of the galaxy with emphasis in choosing regions at different positions within
NGC 3367, for example: regions at larger distances than the bright south-west semicircle
(more than 10 kpc from the center, easily observed in images from the Palomar Sky Surveys),
from the stellar bar’s ends, from structures along and on spiral arms, from structures just
beyond the stellar bar, etc. in order to have enough of them as to be able to compare their
colors and estimate their ages. It included structures on the outside of the intense semicircle
structure with bright surface brightness to the west of the disk.
Table 6 lists the positions, α(J2000.0) and δ(J2000.0) 5 of the different structures
throughout NGC 3367, where we have estimated their magnitudes in the U,B, V, R and
I broadband filters corrected for Galactic extinction. Table 8 is similar to Table 6 and lists
the colors U−B, B−V , and V −I corrected for Galactic extinction of each stellar structure
in NGC 3367 along with their estimated SWB type.
We have estimated the colors of the area in front of the nucleus; the estimated mag-
nitudes were not corrected for intrinsic extinction; a visual extinction has been estimated,
from blue spectroscopy, to be only AV ∼ 0.9 Cid Fernandes et al. (2005). True magnitudes
must be brighter since it is known that there is a lot of molecular gas in the central region
of NGC 3367 (Garćıa-Barreto et al. 2005). At the distance of NGC 3367 (43.6 Mpc) the
absolute magnitude is MV = -13.24 taking into account the Galactic optical extinction. As
5The peak of the I image was anchored (in spatial position) to the peak of the high resolution ra-
dio continuum emission at 8.4 GHz (Garćıa-Barreto, Franco & Rudnick 2002) to the position α(J2000) =
10h 46m 34s.956 δ(J2000) = +13◦ 45′ 02′′.94. Although this is a logical supposition, it needs to be verified
since in other galaxies the peak of the radio continuum emission does not coincide with the compact optical
nucleus as a result of high extinction.
– 9 –
a comparison, the compact nucleus in the barred spiral galaxy NGC 4314, a LINER with a
circumnuclear structure (Garćıa-Barreto et al. 1991), has the following magnitude and col-
ors within an aperture of 6′′, 290 pc: V = 14.07, U −B = 0.51, and B−V = 1.11 (Benedict
1980), MV = -10.93 (at 10 Mpc taking into account the galactic optical extinction); the
compact nucleus of NGC 4314 is reported to have a blue magnitude of B = 16.6 mag per
square arc second (Lynds, Furenlid & Rubin 1973).
Figure 2 shows the U −B versus B − V color color diagram for the different structures
throughout the disk of NGC 3367. As a comparison, Figure 3, shows the corresponding U−B
versus B−V diagram for the Large Magellanic Cloud (Bica et al., 1996) stellar associations
embedded in HII regions (NA in the nomenclature of Bica et al.), star clusters (C), very young
clusters embedded in HII region or compact HII region (NC), stellar associations without
gas (A) and a supernovae remanent. Previuos U,B, V photometry of the SMC and LMC
star clusters indicated that young clusters in the SMC were concentrated along its bar, while
old clusters showed no concentration to the bar (van den Bergh 1981); while the young
clusters in the LMC were in and around the bar (van den Bergh 1981). The difference
between the color color diagrams between the clusters in the magellanic clouds and the
structures in NGC 3367 is noteworthy: the LMC has many very young clusters with colors
equivalent to the SWB 0 type (Searle, Wilkinson & Bagnuolo 1980; Bica, Claŕıa & Dottori
1992; Bica et al., 1996) 6 (see section on ages below) and might also be the result of filling
factor (radius of the aperture used, since the LMC is much closer than NGC 3367), intrinsic
extinction and different chemical enrichment in NGC 3367.
6The location of star clusters of different ages, in the U − B versus B − V color diagram delineate an
average sequence known as SWB 0 to SWB VII (Searle, Wilkinson & Bagnuolo 1980).
– 10 –
Fig. 2.— The color color diagram of different structures throughout NGC 3367 is shown.
Filled hexagon is the compact nucleus (ID 1), open squares are the bright star associations
embedded in HII regions to the west of the on the bright semicircle rim of the disk (ID 2 and
3), open hexagons are the bright stellar associations embedded in HII regions east of the end
of the bar (ID 4 - 6), filled squares are stellar associations to the northeast and southwest
of the bar (ID 37 and 38 respectively), asterisk is the region which includes supernovae
2003aa (ID 42), open triangles are stellar associations in the disk, filled triangles are stellar
associations beyond the semicircle bright end of the western side of the disk (ID 52 and 53).
SWB type (Searle, Wilkinson & Bagnuolo 1980; Bica et al., 1996), SWB 0 have estimated
ages between 0 and 107 yrs, SWB I between 107 and 3 × 107 yrs, SWB II between 3 × 107
and 7 × 107 yrs, SWB III between 7× 107 and 2 × 108 yrs, SWB IVA between 2× 108 and
4× 108 yrs, SWB IVB between 4× 108 and 8× 108 yrs, SWB V between 8× 108 and 2× 109
yrs, SWB VI between 2× 109 and 5× 109 yrs, and SWB VII between 5× 109 and 1.6× 1010
– 11 –
-0.5 0 0.5 1
SWB II
SWB III
SWB IVB 
SWB 0
SWB I
SWB IVA
SWB V
SWB VI
SWB VII
Fig. 3.— The color color diagram of different stellar associations in the Large Magellanic
Cloud (Bica et al., 1996) is shown as a comparison. In their nomenclature, open polygons
are stellar associations embedded in HII regions (NA, U−B in the interval from -1.1 to -0.55
and B−V in the interval -0.4 to 0.2), filled polygons are stellar associations without gas (A,
U − B in the interval from -0.9 to -0.5 and B − V in the interval -0.1 to 0.4), open squares
are very young clusters embedded in HII regions or compact HII regions (NC, U −B in the
interval from -1.05 to -0.3 and B − V in the interval -0.3 to 0.65), and open triangles are
star clusters (C, U −B in the interval from -0.95 to +0.5 and B − V in the interval -0.25 to
0.95) (Bica et al., 1996).
3.3. U B V R I Images
This section shows various images of NGC 3367. Figure 4 is the image in the U filter in a
grey scale and contours, proportional to surface brightness, showing the different structures
throughout NGC 3367.
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Fig. 4.— Optical image, of NGC 3367, is shown in the broadband filter in the Ultraviolet
in greyscale and contours. Contours are in mag arcsec−2, and approximately correspond to
mU ∼ 23.6, 22.6, 21.8, 21.4, 21.1, 20.7, 20.4, 19.6, 18.8, 18.1, and 17.4.
– 13 –
77 78
131243
Right Ascension (J2000)10 46 40 36
Fig. 5.— North east quadrant of the U image showing with circles the positions of different
stellar structures; the circle is ∼ 6′′.8 in diameter which, at the distance of NGC 3367,
corresponds to a linear scale of 1.430 kpc.
– 14 –
      Right Ascension (J2000)
+13 45 00
Fig. 6.— As for Fig. 5 but showing the Southeast quadrant.
– 15 –
Right Ascension (J2000)
Fig. 7.— As for Fig. 5 but showing the Southwest quadrant.
– 16 –
Fig. 8.— As for Fig. 5 but showing the Northwest quadrant.
– 17 –
Figures 5, 6, 7, and 8 show the four different quadrants of NGC 3367 with a circle
indicating the position of the structure observed and its number, according to table 6, with
the circle having the diameter of the aperture utilized for the photometry, that is ∼ 6′′.8
which at the distance of NGC 3367 translates into a linear scale of ∼ 1.4 kpc. Figure 9
shows the I image of the galaxy with a larger area in order to indicate the field stars and
the background spiral galaxy. Figures 10, 11 and 12 show the U −B, B−V and V − I color
images of NGC 3367.
Fig. 9.— Optical image of NGC 3367 in the broadband I filter is shown in greyscale and
contours; contours are in mag arcsec−2 and approximately correspond to m∼20.2, 19.2, 18.7,
18.4, 18.2, and 18. Circles indicate the positions of the stars in the field of NGC 3367, except
for circle in the upper left corner that indicates the position of stellar structure ID 75; each
circle is 8 pixels in radius or ∼ 3′′.4. Stars 86 and 91 were used to estimate the uncertainities
in our photometry when using IRAF tasks qphot (with one aperture) and phot with three
different circular apertures. ID 90 is a background (disk) galaxy.
– 18 –
RIGHT ASCENSION (J2000)
10 46 40 38 36 34 32 30
13 46 15
45 45
44 45
Fig. 10.— U − B color image of the disk galaxy NGC 3367: Greyscale is in arbitrary units
in such a way that white areas indicate brighter ultraviolet emission.
– 19 –
RIGHT ASCENSION (J2000)
10 46 40 38 36 34 32 30
13 46 15
45 45
44 45
Fig. 11.— B − V color image of the disk galaxy NGC 3367.
– 20 –
RIGHT ASCENSION (J2000)
10 46 40 38 36 34 32 30
13 46 15
45 45
44 45
Fig. 12.— V − I color image of the disk galaxy NGC 3367.
4. Discussion
4.1. Spatial distribution of structures with different SWB type
There are 42 stellar structures with age type SWB I 7 out of 81 observed which cor-
respond to 51%. A natural question is, where is their spatial location? Structure ID 1
corresponds to the central innermost stellar association which includes the nucleus of the
galaxy; ID 2 and 3 are two stellar associations embedded in bright HII regions on the western
bright surface brightness edge of the disk at about 10 kpc from the center; ID 4 and 5 lie on
an inner eastern bright surface brightness area which seems to be a spiral arm or part of an
inner ring (just beyond the edge of the stellar bar) at about 4.5 kpc from the center; ID 6
7Approximate intervals of ages to different SWB classes are as follows (Searle, Wilkinson & Bagnuolo
1980; Bica et al., 1996): SWB 0 have ages between 0 and 107 yrs, SWB I have ages between 107 and 3×107
yrs, SWB II have agesbetween 3 × 107 and 7 × 107 yrs, SWB III have ages between 7 × 107 and 2 × 108
yrs, SWB IVAhave ages between 2× 108 and 4× 108 yrs, SWB IVB have ages between 4× 108 and 8× 108
yrs,SWB V have ages between 8×108 and 2×109 yrs, SWB VI have ages between 2×109 and 5×109yrs, and
SWB VII have ages between 5 × 109 and 1.6 × 1010 yrs (Chiosi, Bertelli & Bressan 1988; Girardi & Bica
1993; Anders & Fritze-v. Alvensleben 2003).
– 21 –
Fig. 13.— Histogram of number of structures studied in this work versus their B − V color.
Notice that 61 out of 81 of the structures have B − V color less than 0.5 (blue).
and 48 lie on another structure on an eastern spiral arm, parallel to the arm where ID 4 and
5 lie, at about 8 kpc from the center; ID 7 and 8 lie on the inner most spiral arm north-west
of the center; ID 14 lies on the crooked spiral arm north west of the center at about 6 kpc;
ID 18 lies at about 10 kpc east of the center just outside of the second spiral arm; ID 19 - 22,
25, 27 all lie on the southern spiral arm; ID 30 lies on a circular surface brightness structure
south-west of the south-west end of the stellar bar; ID 31 - 35 and 40 all lie on the western
spiral arm; ID 43 lies on an interarm on the eastern region of the disk at about 8.5 kpc; ID
57 lies on an interarm region west of the nucleus at about 8 kpc.
Structures ID’s 52 - 55, 58, 59, 62 - 74, and 80 lie outside the bright surface brightness
semicircle at distances more than about 13 kpc. The features are detected and shown in
Figs. 4, 5, 6, 7, and 8.
It is important to emphasize that in the central region (ID 1), the western sources
(ID 4 - 6) and the eastern sources (ID 2, 3), there is a large velocity dispersion of ionized
gas, detected through Hα (Garćıa-Barreto & Rosado 2001) and in the molecular gas CO
(Garćıa-Barreto et al. 2005).
In summary, most of the structures with age type SWB I lie close or on spiral arms.
Perhaps the most important result of the spatial distribution of structures with age type
SWB I is that several lie outside of the eastern bright surface brightness disk, ID 58 and 59
to the south, ID 65, 66, 69, 70, to the east while ID 53, 71 - 74 lie to the western side and ID
75 lies well outside the disk to the north-eastern end. The colors of structures ID 58, 59, 71 -
74 and 75 suggest that they are newly formed stellar structures and yet they lie at distances
beyond the bright visible disk of NGC 3367, that is beyond 10 kpc from the center.
– 22 –
4.2. Estimated ages of the structures throughout NGC 3367
It is difficult to speak about ages of the different structures throughout NGC 3367
mainly because, as we have seen, different structures could indicate star associations em-
bbeded in HII regions, very young star cluster embedded in HII regions, star associations
not associated with gas, star associations in or around the nucleus, and other combinations.
Among some of the problems with estimating the magnitudes of different structures are: fill-
ing factor, spatial distribution of structure within the aperture, and the fact that we used a
circular aperture. We realize that with our circular aperture diameter, of 6′′.8 ∼ 1.4 kpc, for
estimating magnitudes and colors one can not detect individual star clusters in this galaxy.
However, the study of star clusters with U,B, V, R, and I photometry and colors, and their
derived ages in the LMC (Searle, Sargent & Bagnuolo 1973; Searle, Wilkinson & Bagnuolo
1980) might be taken as an excellent reference to compare the U,B, V, R, and I colors of the
different structures throughout NGC 3367 and estimate their ages if only one were to assume
that the colors were equivalent, the chemical abundance were similar, have the same metal-
licity as in the LMC (which of course there is no reason to be an absolute valid assumption)
and more important we might use the SWB ages if one ignores the internal reddening.
ID 42, which includes supernova 2003AA, (asterisk in Figs. 2 and 4) has colors similar
to SWB II. Structures ID 52 and ID 53, beyond the bright western high surface brightness
rim of NGC 3367 (filled triangles in Fig. 2) have equivalent colors to clusters SWB IVB
and V. ID 37 and ID 38 are the structures north-east and south-west respectively of the
stellar bar (filled squares in Fig. 2) have colors similar to SWB VI, indicating old stellar
populations, but this result needs to be taken with caution since there the colors have not
been corrected for intrinsic extinction as a result of the probable existence of molecular gas
(CO, H2) and dust at least to the southwest side of the bar (Garćıa-Barreto et al. 2005).
Figure 12 shows the histogram of the number of structure throughout NGC 3367 versus
the color B − V where there is a large number of structures with blue colors, B − V ≤ 0.5.
Figure 13 shows the histogram of age groups according to SWB types (assuming that the
models for star clusters in the LMC also apply to the structures and angular resolution
observed in NGC 3367) where 64% of the structures observed have age types smaller or
equal than SWB type II or less than 70 Myrs.
Figs. 13 and 14 suggest that a large number of structures throughout NGC 3367 are
relatively blue and young structures. This number of young structures would probably
increase as one were able to somehow correct for intrinsic extinction, and different metallicity.
5. Conclusions
To conclude, we have obtained several images in the broadband filters U,B, V, R, and
I in order to estimate the optical magnitudes and colors of 81 different stellar structures
throughout the disk of NGC 3367. The structures were chosen from the images in the I and
U filters by eye at different locations of the disk of the galaxy in order to have enough of
them as to be able to compare their colors as a function of their spatial location. It included
structures to the north-east, south and west, well outside of the semicircle structure with
bright surface brightness.
Our estimated magnitudes for the NGC 3367, after correcting for Galactic extinction are
U = 11.70±0.1, B = 11.91±0.1,V = 11.52±0.1, R = 11.05±0.1, and I = 10.43±0.1. NGC
– 23 –
Fig. 14.— Histogram of number of structures studied in this work versus age group, SWB
type. Notice that 86% (70 out of 81) of the structures have SWB types I, II or III. This
number would increase as a result of intrinsic extinction.
3367 global colors, after being corrected for Galactic extinction are U−B = −0.21, B−V =
0.39, B−I = 1.48. All images except the image in V were convolved with an appropiate two
dimensional gaussian function in order to have a final of 2′′.2 full width at half maximum,
since the seeing was different for each filter and was about 1′′.7 to 2′′.2. The 81 stellar
structures reported in this paper were selected mainly from the U and the I images based on
the location in the disk in order to have as many as possible from different positions in NGC
3367. We have made careful analysis of the calibration methods to estimate magnitudes
and have compared different IRAF tasks, in particular, qphot and phot utilizing different
apertures in order to estimate the uncertainities in the final magnitudes at different filters
with 9 stars in M 67 as our standards. In the case of estimating the magnitudes for the
structures throughout the disk in NGC 3367, we have made careful analysis utilizing different
IRAF tasks, in particular, qphot and phot using different aperture diameters for the bright
stars in the field of NGC 3367 in order to estimate the uncertainities in the final magnitudes
at different filters before estimating the final magnitudes reported for the different structures
in NGC 3367. The magnitudes reported here for the structures in NGC 3367 were estimated
using an aperture radius of 8 pixels (∼ 3′′.4 ∼ 715 pc).
We were able to estimate the optical magnitudes U,B, V, R, and I and colors U−B, B−
V, U − V, and V − I for 81 different stellar structures throughout the disk in NGC 3367. It
is difficult to estimated the ages of the structures in NGC 3367 given our circular aperture
diameter, equivalent to 6′′.8 ∼ 1.4 kpc. However if their colors were taken as representative
as the colors of star clusters (studied by many other authors with better angular resolution,
– 24 –
appropiate chemical abundance and current theoretical star evolutionary tracks) in the LMC
many have colors equivalent to cluster types SWB I, and SWB II suggesting that many are
young associations with only tens of millions of years of age.
We found 41 structures out of 81 (50%) with age type SWB I. Several of those structures
lie near or in spiral arms; some lie outside of the bright surface brightness visible disk (for
example the POSS image).
In order to understand better the large scale environment of NGC 3367 it would also
be very important to determine the large scale spatial distribution and kinematics of atomic
hydrogen (HI) and new observations with high angular resolution of the emission of the
molecular gas (CO, H2) in the center of NGC 3367.
Acknowledgements
JAGB and HMHT thank the staff of the Observatorio Astronomico Nacional at San
Pedro Mártir, Baja California, México for the help in the observations. HMHT acknowl-
edges support from grant CONACyT (México) 42810. JAGB acknowledges partial financial
support from DGAPA (UNAM, México) grant IN107806-2. The authors would like to thank
the anonimous referee for his (her) comments and suggestions on how to improve this paper.
– 25 –
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– 28 –
Table 1: General Properties of the barred disk galaxy NGC 3367
Characteristic Value Reference
Hubble Type (RC3) SB(rs)c 3
Nucleus spectral type Sy 2-like, HII 1,2
U mag 11.89 ± 0.15 3
B mag 12.05 ± 0.14 3
V mag 11.50 ± 0.14 3
I mag 10.60 ± 0.07 4
Vsys(HI) 3030 ± 8 km s
Vsys(opt) 2850 ± 50 km s
Vsys(FP
a) 3032 ± 3 km s−1 6
Vsys(CO) 3035 ± 5 km s
α(J2000) 10h 46m 34.95s 8
δ(J2000) +13◦ 46′ 02.9′′ 8
log LB/L⊙ 10.68 9
Photometric major axis P.A. 109◦ ± 4 10
Photometric inclination 6◦ ± 1 10
Major kinematic axis P.A. 51◦ ± 3 6
Inclination of disk (from kinematics) 30
Stellar bar P.A. 65◦ ± 5 11
Stellar bar diameter 32′′ ∼ 6.7 kpc 11
M(HI) 7× 109 M⊙ 5
M(H2), r=27
′′ 2.6× 109 M⊙ 7
M(H2), r=4
′′.5 5.9× 108 M⊙ 7
Visual extinction, Av/2 toward nucleus
b ∼ 75 mag 7
Total Radio Continuum (20 cm) flux density 119.5 mJy 12
Sum flux density (20 cm) from extended lobes 39 mJy 8
Projected distance of each synchrotron lobe ∼6 kpc 8
Position angle of inner radio continuum synchroton emission ∼ 46◦± 6 8
Position angle of synchrotron lobes ∼ 30◦ ± 20 8, 13
References: 1) Véron-Cetty & Véron (1986), 2) Ho, et al. (1997a), 3) de Vaucouleurs et al. (1993) RC3, 4) Nasa Extragalactic
Database (NED), 5) Huchtmeier & Seiradakis (1985), 6) Garćıa-Barreto & Rosado (2001), 7) Garćıa-Barreto et al. (2005), 8)
Garćıa-Barreto, Franco & Rudnick (2002), 9) Tully (1988), 10) Grosbøl (1985), 11) Garćıa-Barreto et al. (1996a,b), 12) Condon
et al. (1998), 13) Garćıa-Barreto et al. (1998)
a From Fabry-Perot Hα optical interferometry; b Maloney (1990).
– 29 –
Table 2: Journal of observations, average seeing and exposure time.
U B V R I
Seeing ∼ 2′′.0 ∼ 2′′.1 ∼ 2′′.2 ∼ 1′′.80 ∼ 1′′.70
∆λ (Å) 600 950 1400 400 1600
λcentralefective (Å) 3540 4330 5750 6340 8040
M67 8×30s 8×30s 8×15s 8×5s 8×5s
NGC 3367 5×600s 5×600s 5×600s 8×300s 8×300s
Table 3: Our estimated UBVRI photometry of stars in M67 with IRAF phot, and those
observed by other groups
Our ID ID1,2 U(ours) U1 B(ours) B1 V (ours) V 1 R(ours) R1 I(ours) I2
1 48,14c 13.79 13.76 13.75 13.74 13.17 13.16 12.84 12.84 12.50 12.49
2 16,15c 12.92 12.90 12.85 12.86 12.27 12.27 11.94 11.95 11.59 11.57
33 49,17c 13.85 13.84 13.80 13.78 13.21 13.20 12.88 12.86 12.53 12.50
4 28,18c 13.36 13.37 13.35 13.37 12.89 12.91 12.63 12.65 12.32 12.33
5 52,19 13.84 13.84 13.79 13.80 13.21 13.22 12.88 12.89 12.53 12.53
6 27,20c 13.37 13.40 13.35 13.35 12.78 12.78 12.46 12.46 12.10 12.12
7 13,21c 12.62 12.65 12.59 12.60 12.13 12.14 11.86 11.87 11.54 11.57
8 37,22c 13.68 13.70 13.41 13.43 12.61 12.63 12.16 12.17 11.72 11.74
9 44,23 13.69 13.72 13.66 13.65 13.09 13.09 12.77 12.77 12.42 12.43
1 (Guilliland et al., 1991); 2 (Chevalier & Ilovaisky 1991); 3 Position of star #3 is: α(B1950.0)=08h 48m 37s.5,
δ(B1950.0)=+11◦ 57′ 23′′.4; as a comparison, the position and magnitude reported in the USNO-B Star Catalog (Monet et al.
2003), for a star probably associated with star #3 is: α(B1950.0)=08h 48m 37s.95, δ(B1950.0)=+11◦ 57′ 57′′.9 magB1 = 13.98,
magB2 = 13.54
Table 4: UBVRI estimated photometry of bright stars in the field of NGC 3367 with IRAF
task qphot, aperture (apr), and width of ring (wor)
apr = 23 pixels (9′′.8), wor = 5′′
ID α(J2000.0) δ(J2000.0) U B V R I
85 10h 46m 27s.56 +13◦ 43′ 46′′.0 13.91 13.51 12.87 12.47 12.22
90 10h 46m 30s.60 +13◦ 42′ 28′′.6 13.13 13.00 12.68 12.37 12.12
– 30 –
Table 5: UBVRI Comparative Photometry of bright stars in the field of NGC 3367, using
IRAF task phot with three aperture (apr) radii: apr 20 pixels ∼ 8′′.5, 23 pixels ∼ 9′′.8 and
26 pixels ∼ 11′′.1
apr = 20 pixels (8′′.5)
ID α(J2000.0) δ(J2000.0) U B V R I
85 10h 46m 27s.56 +13◦ 43′ 46′′.0 13.87 13.46 12.82 12.43 12.12
90 10h 46m 30s.60 +13◦ 42′ 28′′.6 13.09 12.95 12.63 12.32 12.02
apr = 23 pixels (9′′.8)
85 10h 46m 27s.56 +13◦ 43′46′′.0 13.87 13.46 12.81 12.42 12.11
90 10h 46m 30s.60 +13◦ 42′28′′.6 13.09 12.95 12.62 12.31 12.01
apr = 26 pixels (11′′.1)
85 10h 46m 27s.56 +13◦ 43′46′′.0 13.86 13.45 12.81 12.42 12.09
90 10h 46m 30s.60 +13◦ 42′28′′.6 13.09 12.95 12.62 12.31 11.99
– 31 –
Table 6. UBV RI Photometry, corrected for Galactic extinction, of structures throughout
NGC 3367 using IRAF task phot using an aperture with radius 8 pixels ∼ 3′′.41 ∼ 715 pc
ID α(J2000.0) δ(J2000.0) U B V R I
11 34s.9492 45′ 02′′ .82 14.84 15.39 14.92 14.39 13.92
2 31s.71 45′ 00′′ .0 16.49 17.28 17.05 16.82 16.45
3 31s.70 44′ 54′′ .1 16.45 17.24 17.00 16.79 16.43
4 36s.62 45′ 09′′ .2 16.65 16.91 16.47 16.03 15.50
5 36s.45 45′ 05′′ .0 16.64 16.92 16.47 16.02 15.48
6 37s.46 45′ 11′′ .7 16.89 17.31 17.10 16.79 16.31
7 34s.66 45′ 16′′ .3 16.98 17.27 16.84 16.42 15.82
8 33s.96 45′ 10′′ .2 16.73 17.05 16.62 16.20 15.62
9 36s.62 45′ 18′′ .6 17.09 17.24 16.79 16.36 15.84
10 36s.44 45′ 15′′ .3 17.16 17.24 16.72 16.26 15.67
11 35s.68 45′ 22′′ .2 17.58 17.71 17.24 16.77 16.18
12 36s.10 45′ 28′′ .4 17.42 17.63 17.22 16.83 16.27
13 35s.73 45′ 28′′ .0 17.56 17.72 17.31 16.91 16.36
14 33s.40 45′ 20′′ .8 17.51 17.83 17.48 17.08 16.51
15 32s.84 45′ 13′′ .2 17.82 17.93 17.49 17.06 16.43
16 32s.29 45′ 05′′ .2 17.75 18.02 17.68 17.30 16.71
17 35s.67 44′ 39′′ .9 17.22 17.49 17.09 16.69 16.14
18 37s.91 45′ 03′′ .3 18.58 19.09 18.70 18.29 17.64
19 37s.47 44′ 29′′ .8 18.05 18.53 18.33 17.93 17.48
20 36s.47 44′ 26′′ .0 17.52 17.90 17.49 17.08 16.58
21 36s.02 44′ 27′′ .1 17.76 18.02 17.57 17.15 16.60
22 36s.03 44′ 24′′ .3 17.32 17.83 17.47 17.07 16.63
23 35s.20 44′ 23′′ .6 17.42 17.66 17.32 16.95 16.43
24 35s.30 44′ 23′′ .7 17.38 17.62 17.30 16.93 16.42
25 34s.17 44′ 25′′ .9 17.57 17.84 17.43 17.06 16.50
26 33s.71 44′ 26′′ .6 17.66 17.94 17.59 17.22 16.68
27 33s.42 44′ 38′′ .6 17.35 17.62 17.25 16.87 16.28
28 33s.40 44′ 44′′ .5 17.54 17.67 17.24 16.81 16.21
29 33s.31 44′ 48′′ .2 17.45 17.59 17.15 16.75 16.12
30 32s.84 44′ 45′′ .7 17.53 17.88 17.50 17.15 16.54
31 31s.68 45′ 07′′ .7 17.78 18.26 17.99 17.66 17.10
32 32s.06 45′ 20′′ .3 17.45 17.89 17.58 17.27 16.79
33 32s.16 45′ 22′′ .4 17.43 17.87 17.58 17.27 16.80
34 31s.93 45′ 24′′ .3 17.47 17.91 17.68 17.36 16.88
35 32s.02 45′ 30′′ .7 17.49 18.04 17.78 17.46 17.02
36 35s.45 45′ 14′′ .6 17.61 17.57 16.91 16.43 15.76
373 35s.68 45′ 06′′ .2 17.61 17.25 16.40 15.84 15.20
384 34s.15 45′ 00′′ .5 17.50 17.29 16.48 15.93 15.25
39 34s.69 45′ 50′′ .0 18.69 18.96 18.63 18.24 17.75
40 33s.63 45′ 51′′ .4 18.35 18.72 18.45 18.12 17.70
41 36s.32 45′ 42′′ .3 18.16 18.31 17.96 17.62 17.12
425 36s.74 45′ 32′′ .9 18.14 18.29 17.85 17.42 16.91
43 37s.03 45′ 28′′ .1 17.88 18.16 17.72 17.28 16.77
44 37s.39 45′ 35′′ .4 18.14 18.32 17.99 17.62 17.09
45 34s.42 45′ 31′′ .9 17.73 17.83 17.45 17.07 16.52
46 33s.23 45′ 26′′ .9 17.64 17.82 17.41 17.02 16.48
47 35s.01 44′ 47′′ .3 17.67 17.62 17.05 16.59 15.94
48 37s.02 44′ 59′′ .1 17.58 17.86 17.44 17.00 16.46
49 36s.37 44′ 48′′ .5 17.82 17.88 17.37 16.90 16.31
50 35s.62 44′ 49′′ .1 17.65 17.75 17.20 16.72 16.09
51 35s.82 44′ 54′′ .9 17.38 17.49 16.97 16.52 15.89
52 31s.03 44′ 49′′ .6 19.42 19.60 19.01 18.58 17.79
53 32s.06 44′ 31′′ .5 19.21 19.67 19.05 18.61 17.81
54 38s.19 44′ 38′′ .1 19.04 19.34 19.01 18.61 17.92
55 38s.32 44′ 44′′ .2 19.32 19.56 19.12 18.66 18.02
56 36s.95 44′ 37′′ .0 18.51 18.63 18.18 17.76 17.13
57 32s.44 44′ 47′′ .7 17.96 18.23 17.83 17.42 16.84
58 36s.22 44′ 09′′ .0 19.70 19.93 19.48 19.07 18.30
59 36s.60 44′ 10′′ .4 19.42 19.81 19.43 19.00 18.29
60 37s.12 45′ 44′′ .9 18.90 19.02 18.71 18.28 17.77
61 37s.55 45′ 44′′ .3 18.62 18.84 18.63 18.23 17.86
62 35s.56 46′ 04′′ .5 19.68 18.84 18.63 18.23 17.86
63 34s.39 46′ 04′′ .5 19.61 19.80 19.63 19.27 18.96
64 33s.87 46′ 06′′ .0 19.81 19.90 19.85 19.36 19.12
65 32s.70 45′ 53′′ .1 19.50 19.69 19.46 19.18 18.70
66 39s.05 44′ 52′′ .2 19.57 19.87 19.32 18.96 18.21
67 39s.39 45′ 04′′ .5 20.07 20.12 19.63 19.08 18.49
68 39s.47 45′ 08′′ .3 20.10 20.23 19.86 19.29 18.60
69 38s.72 45′ 01′′ .7 19.96 20.07 19.56 19.16 18.18
70 39s.10 44′ 53′′ .7 19.62 19.85 19.35 18.97 18.23
71 31s.10 44′ 18′′ .4 20.42 20.70 20.31 19.89 18.76
72 30s.98 44′ 13′′ .9 20.51 20.92 20.48 20.17 18.88
73 31s.07 44′ 07′′ .1 20.14 21.24 20.66 20.33 19.16
74 30s.30 45′ 19′′ .5 20.61 21.01 21.34 20.58 19.43
75 43s.42 46′ 10′′ .0 20.90 21.30 20.79 20.02 20.73
76 36s.69 45′ 08′′ .2 16.73 16.99 16.55 16.12 15.62
77 35s.94 45′ 10′′ .6 17.46 17.31 16.59 16.09 15.44
78 33s.99 44′ 46′′ .8 18.01 18.02 17.36 16.84 16.15
79 36s.44 45′ 38′′ .6 18.25 18.28 17.93 17.56 17.04
80 39s.07 45′ 05′′ .7 20.31 20.21 19.53 19.13 18.27
81 35s.07 45′ 21′′ .7 18.27 18.20 17.60 17.12 16.41
1Centermost region (nucleus + part of bulge) of the galaxy;
2Positions of peak of emission, in afilter where the intensity was strongest,
α(J2000.0)=10h 46m; δ(J2000.0)=+13◦ ;
3northeast region of the stellar bar;
4southwest region of the stellar bar;
– 32 –
5position of peak which includes supernova 2003AA type Ia (Swift, Pugh & Li
2003; Filippenko & Chornock 2003).
– 33 –
Table 7. UBV RI Photometry of stars and a background galaxy in the field of NGC 3367,
corrected for Galactic extinction, using IRAF task phot using an aperture with radius 8
pixels ∼ 3′′.41 ∼ 715 pc
ID α(J2000.0) δ(J2000.0) U B V R I
821 33s.10 45′ 11′′ .4 17.91 17.94 17.37 16.86 16.21
83 28s.56 45′ 54′′ .7 19.66 19.04 18.13 17.52 17.04
84 42s.53 44′ 33′′ .5 18.20 17.94 17.19 16.75 16.36
852 27s.56 43′ 46′′ .0 13.93 13.54 12.91 12.51 12.26
86 29s.34 44′ 12′′ .5 21.85 21.73 20.29 19.40 17.93
87 29s.78 43′ 27′′ .9 21.64 20.99 20.09 19.29 18.45
88 39s.28 44′ 08′′ .0 20.63 20.34 19.63 18.65 17.32
893 28s.62 42′ 41′′ .5 20.63 20.34 19.13 18.43 17.56
904 30s.60 42′ 28′′ .6 13.16 13.03 12.73 12.41 12.17
1dim star within NGC 3367;
2bright star south west in the field of NGC 3367; this star was taken as a test
star in order to estimate the uncertainities when obtaining its magnitudes with
different aperture radii;
3small galaxy with weak surface brightness to the south south west in the field
of NGC 3367;
4bright star south south west in the field of NGC 3367; this star was taken as
a test star in order to estimate the uncertainities when obtaining its magnitudes
with different aperture radii.
– 34 –
Table 8. U-B, B-V, V-I Colors of Stellar Structures in NGC 3367.
ID U − B B − V V − I SWB type1
12 -0.55 0.47 1.00 I
2 -0.79 0.23 0.60 I
3 -0.79 0.24 0.57 I
4 -0.26 0.44 0.97 I
5 -0.28 0.45 0.99 I
6 -0.42 0.21 0.79 I
7 -0.29 0.43 1.02 I
8 -0.32 0.43 1.00 I
9 -0.15 0.45 0.95 II
10 -0.08 0.52 1.05 III
11 -0.13 0.47 1.06 II
12 -0.21 0.41 0.95 II
13 -0.16 0.41 0.95 II
14 -0.32 0.35 0.97 I
15 -0.11 0.44 1.06 III
16 -0.27 0.34 0.97 I
17 -0.27 0.40 0.95 I
18 -0.51 0.39 1.05 I
19 -0.48 0.20 0.84 I
20 -0.38 0.41 0.91 I
21 -0.26 0.51 0.97 I
22 -0.51 0.36 0.84 I
23 -0.24 0.34 0.89 I
24 -0.24 0.32 0.88 I
25 -0.27 0.41 0.93 I
26 -0.28 0.35 0.91 I
27 -0.27 0.37 0.97 I
28 -0.13 0.43 1.03 II
29 -0.14 0.44 1.03 II
30 -0.35 0.38 0.96 I
31 -0.48 0.27 0.89 I
32 -0.44 0.31 0.79 I
33 -0.44 0.29 0.78 I
34 -0.44 0.23 0.80 I
35 -0.55 0.26 0.76 I
36 +0.04 0.66 1.15 VII
373 +0.36 0.85 1.20 VI
384 +0.21 0.81 1.23 VII
39 -0.27 0.33 0.88 I
40 -0.37 0.27 0.75 I
41 -0.15 0.35 0.84 II
425 -0.15 0.44 0.94 II
43 -0.28 0.44 0.95 I
44 -0.18 0.33 0.88 II
45 -0.10 0.38 0.93 III
46 -0.18 0.41 0.93 II
47 +0.05 0.57 1.11 IVB
48 -0.28 0.42 0.98 I
49 -0.06 0.51 1.06 IVA
50 -0.10 0.55 1.11 III
51 -0.11 0.52 1.08 III
52 -0.18 0.59 1.22 I
53 -0.44 0.60 1.24 I
54 -0.30 0.33 1.09 I
55 -0.24 0.44 1.10 I
56 -0.12 0.45 1.05 III
57 -0.27 0.40 0.99 I
58 -0.23 0.45 1.18 I
59 -0.39 0.38 1.14 I
60 -0.12 0.31 0.94 III
61 -0.22 0.21 0.77 II
62 -0.01 0.17 0.75 III
63 -0.19 0.17 0.67 II
64 -0.09 0.05 0.73 III
65 -0.19 0.23 0.76 II
66 -0.30 0.55 1.11 I
67 -0.05 0.49 1.14 IVA
68 -0.13 0.37 1.26 III
69 -0.11 0.51 1.38 III
70 -0.23 0.50 1.12 I
71 -0.28 0.38 1.55 I
72 -0.41 0.44 1.60 I
73 -1.10 0.58 1.50 I
74 -0.40 -0.33 1.91 II
75 -0.40 0.51 0.36 I
76 -0.26 0.44 0.94 I
77 +0.15 0.72 1.15 VII
78 -0.01 0.66 1.21 VII
79 -0.03 0.35 0.89 IVA
80 +0.10 0.68 1.26 VII
81 +0.07 0.60 1.19 IVB
1SWB type (Searle, Wilkinson & Bagnuolo
1980; Bica et al., 1996). Each type suggest an
approximate interval of age to different SWB
classes as follows: SWB 0 have ages between 0
and 107 yrs, SWB I have ages between 107 and
3×107 yrs, SWB II have ages between 3×107 and
7 × 107 yrs, SWB III have ages between 7 × 107
and 2 × 108 yrs, SWB IVA have ages between
2 × 108 and 4 × 108 yrs, SWB IVB have ages
– 35 –
between 4×108 and 8×108 yrs, SWB V have ages
between 8 × 108 and 2 × 109 yrs, SWB VI have
ages between 2 × 109 and 5 × 109 yrs, and SWB
VII have ages between 5 × 109 and 1.6 × 1010 yrs;
2Centermost region (nucleus + part of bulge) of
the galaxy;
3northeast region of the stellar bar;
4southwest region of the stellar bar;
5position of peak which includes supernova
2003AA type Ia Swift, Pugh & Li (2003);
Filippenko & Chornock (2003);
– 36 –
Table 9. UBVI Colors of foreground stars and a background galaxy in the field of NGC
3367.
ID U − B B − V V − I type1
822 -0.03 +0.57 1.16 F7V
83 +0.62 +0.91 1.09 K3V
84 +0.26 +0.75 0.83 G8V
853 +0.39 +0.63 0.65 G2III
86 -0.88 +1.44 2.36 K5III
87 +0.65 +0.90 1.64 G7III
88 +0.29 +0.71 2.31 K3III
894 +0.29 +1.21 1.57 spiral
905 +0.13 +0.30 0.56 F1III
1approximate spectral type
Mihalas & Binney (1981);
2dim star within NGC 3367;
3bright star south west in the field of NGC
3367; this star was taken as a test star in order
to estimate the uncertainities when obtaining
its magnitudes with different aperture radii;
4galaxy with weak surface brightness south
south west in the field of NGC 3367;
5bright star south south west in the field of
NGC 3367; this star was taken as a test star in
order to estimate the uncertainities when ob-
taining its magnitudes with different aperture
radii.
	Introduction
	Observations and Data Reduction
	Uncertainities in the Photometry
	As a result of the Method
	Standard Stars as calibrators
	Results
	Total Magnitudes and Colors
	U B V R I Photometry of Star Associations and structures
	U B V R I Images
	Discussion
	Spatial distribution of structures with different SWB type
	Estimated ages of the structures throughout NGC 3367
	Conclusions

  We report new detailed surface U, B, V, R, and I photometry of 81 stellar
structures in the disk of the barred galaxy NGC 3367. The images show many
different structures indicating that star formation is going on in the most
part of the disk. NGC 3367 is known to have a very high concentration of
molecular gas distribution in the central regions of the galaxy and bipolar
synchrotron emission from the nucleus with two lobes (at 6 kpc) forming a
triple structure similar to a radio galaxy. We have determined the U, B, V, R,
and I magnitudes and U - B, B - V, U - V, and V - I colors for the central
region (nucleus), a region which includes supernovae 2003 AA, and 79 star
associations throughout NGC 3367. Estimation of ages of star associations is
very difficult due to several factors, among them: filling factor, metallicity,
spatial distribution of each structure and the fact that we estimated the
magnitudes with a circular aperture of 16 pixels in diameter, equivalent to
$6''.8\sim1.4$ kpc. However, if the colors derived for NGC 3367 were similar to
the colors expected of star clusters with theoretical evolutionary star tracks
developed for the LMC and had a similar metallicity, NGC 3367 show 51 percent
of the observed structures with age type SWB I (few tens of Myrs), with seven
sources outside the bright surface brightness visible disk of NGC 3367.

Introduction
It is a continuous topic of study how a galaxy evolves with time (Larson 1977; van der Kruit
1989; Pfenniger 2000). Integrated photometry of star clusters and star associations in a
galaxy can provide fundamental insight on the star-formation history (Bica et al., 1996).
U,B, V colors of galaxies depend mainly on their history of star formation (Searle, Sargent & Bagnuolo
1973; Larson & Tinsley 1978). The fact that morphologically peculiar galaxies show bluer
http://arxiv.org/abs/0704.1450v1
– 2 –
U −B colors in the two color diagram suggests that galaxies with peculiar appearance have
experienced anomalous star formation histories characterized by recent burst. Models with
recent bursts of star formation (SFR) predict colors that in general lie off the normal relation
for models with monotonically decreasing SFR (Larson & Tinsley 1978), for example, a very
recent strong burst results in an excessively blue U−B for a given B−V (Larson & Tinsley
1978). Integrated photometry of star clusters and star associations in a galaxy would provide
fundamental insight on the star-formation history (Bica et al., 1996).
NGC 3367, the disk galaxy with a stellar bar of our study, is noteworthy because of
observational characteristics, some of them are: 1) it shows a bipolar synchrotron outflow
from the nucleus with a compact unresolved source with deconvolved diameter less than 65
pc, and two large lobes straddling the nucleus with a total, projected extent on the sky,
from the north-east to the south-west lobe of about 12 kpc (an image like a radio galaxy,
but from, a nearby late disk galaxy); only the south-west lobe shows polarized emission,
suggesting that this lobe is out of the plane of the disk and is closer to the observer than
the other lobe (Garćıa-Barreto et al. 1998; Garćıa-Barreto, Franco & Rudnick 2002); 2)
the axis of the ejected outflow is highly inclined with respect to the axis of rotation of the
disk of the galaxy (Garćıa-Barreto et al. 1998; Garćıa-Barreto, Franco & Rudnick 2002);
3) there is a lot of molecular gas mostly concentrated in the central 9′′ with an unresolved
source with M(H2) ∼ 5.9× 10
8 M⊙; this molecular mass suggests an optical extinction value
Av(l) ∼ 75 magnitudes toward the nucleus (Garćıa-Barreto et al. 2005) (as it has been
detected through its CO(J=1-0) emission with the OVRO mm Array1); its total molecular
(H2) mass within 11.4 kpc diameter is M(H2) ∼ 2.6× 10
9 M⊙ (Garćıa-Barreto et al. 2005);
4) it shows a bright southwest optical structure (resembling a “bow shock”) with a collection
of Hα knots at a galactocentric radius of about 10 kpc from the nucleus (Sandage 1961;
Garćıa-Barreto, Franco & Carrillo 1996a; Garćıa-Barreto et al. 1996b), 5) it has crooked
arms in its northwest side, and 6) it seems to be isolated with no similar-diameter galaxy in
its proximity; NGC 3367 lies, behind the Leo group of galaxies, at a distance of 43.6 Mpc,
with a closest companion lying at a projected distance of ≈ 563 kpc or 18 optical diameters
away (Garćıa-Barreto, Carrillo & Vera-Villamizar 2003).
NGC 3367 is an SBc(s) barred spiral galaxy with a stellar bar structure of diame-
ter ≈ 32′′ ∼ 6.7 kpc oriented at a position angle (P.A.) ≈ 65 − −70◦. The disk is in-
clined with respect to the plane of the sky at ∼ 30◦ (Garćıa-Barreto & Rosado 2001).
NGC3367 has an X ray luminosity much larger than any normal spiral galaxy (Gioia et al.
1990; Stocke et al. 1991; Fabbiano, Kim & Trinchieri 1992). Its radio continuum emission
at a 4′′.5 angular resolution shows weak radio continuum emission extended throughout
the disk (Garćıa-Barreto et al. 1998). From Fabry Perot observations of the Hα emis-
sion it is deduced that the kinematic major axis lies projected on the disk at a P.A.
of 51◦ (Garćıa-Barreto & Rosado 2001). Its optical spectrum shows moderately broad
Hα+[NII] lines with FWHM∼ 650 km s−1, but its emission of Hβ is stronger than its
emission of [OIII]λ5007Å and there is weak emission of He II λ4686Å suggesting the ex-
istence of WR stars (Véron-Cetty & Véron 1986; Véron, Gonçalves & Véron-Cetty 1997;
Ho, Filippenko & Sargent 1997). NGC 3367 has been clasiffied as an HII nucleus (from
the optical line ratios; see (Ho et al., 1997a) and normal content of atomic hydrogen with
1The Owens Valley Radio Observatory millimeter array is operated by Caltech and it is supported by the
National Science Foundation grant AST 99-81546
– 3 –
MHI ∼ 7× 10
9 M⊙ (Huchtmeier & Seiradakis 1985). Table 1 lists relevant information for
NGC 3367 coming from the literature.
Previous U,B, V, I phometry of NGC 3367 has been obtained for the whole galaxy
with magnitudes reported in RC3 (de Vaucouleurs et al., 1993) and compiled in the NASA
Extragalactic Data Base (NED)2 as listed in Table 1; previously reported colors are as follows:
U − B = −0.16, B − V = 0.55, B − I = 1.45. Larson & Tinsley (1978) have discussed
different factors that would affect the U,B, V colors, among them are reddening (galactic
and intrinsic), gaseous emission lines and nonthermal emission, chemical composition and
initial mass function (IMF). The color B − V of NGC 3367 agrees with the color expected
from a late type disk galaxy (Allen 1976; Larson & Tinsley 1978); however the U −B color
of NGC 3367 certainly lie above the mean value of normal disk galaxies and the position in
the U−B vs B−V (Larson & Tinsley 1978) is more in agreement with the statistical colors
of galaxies from the Arp Atlas of peculiar galaxies 3. These colors of NGC 3367 suggest that
this late type barred galaxy is currently having many regions with recent star formation.
Although galactic reddening is a major source of uncertainity in the U,B, V colors, for
this galaxy it is not a major concern given its lalitude, b = +58◦. We report our magnitude
estimates for the different structures corrected for Galactic extinction. Gaseous emission
lines, different chemical composition and different initial mass function may contribute to
the uncertainities of the expected colors (Larson & Tinsley 1978).
This paper reports new U,B, V, R, I photometry of 81 individual structures throughout
NGC 3367 using the 84 cm optical telescope in San Pedro Mártir, Baja California, México
(Richter, et al. 2005). For the data reduction and analysis we used the IRAF4 task phot
with an aperture radius of 8 pixels (3′′.41 ∼ 715 pc). The existence of a close connection
between violent galactic dynamical phenomena is consistent with theoretical expectations
that high velocity collisions and shock fronts should be effective in compressing gas to high
densities and triggering rapid star formation. Section 2 reports the observations, §3 reports
the results and §4 gives the discussion and finally §5 describes the conclusions.
2. Observations and Data Reduction
The observations were carried out using the 84 cm optical telescope at the Observatorio
Astronómico Nacional at San Pedro Mártir, Baja California, México on 2005, March 8 and
9. We used a CCD camera Site3 with a 1024×1024 pixels; each pixel size is equivalent to
2NED is operated by the Jet Propulsion Laboratory, California Institute of Technology under contract
with the National Aeronautics and Space Administration.
3As a comparison the U − B and B − V of an early type (elliptical) galaxy are U − B ≥ +0.55, and
B − V ≥ +0.80 (Larson & Tinsley 1978).
4The IRAF package is written and supported by the IRAF programming group at the National Optical
Astronomy Observatories (NOAO) in Tucson, Arizona. NOAO is operated by the Association of Universities
for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation
(NSF).
– 4 –
0′′.426 and we did not use any binning. Attached to the camera was a filter box. A journal of
the photometric observations is given in Table 2. Column (1) give a characteristic; columns
(2)-(6) give the filters; rows indicate the data for each column, seeing, central wavelength
and total width of the filter used, and the number of frames times the integration time (in
seconds) of each of the images (M67 and NGC 3367) in each filter. Images were debiased,
trimmed, and flat-fielded using standard IRAF procedures. First, the bias level of the CCD
was subtracted from all exposures. A run of 10 bias images was obtained per night, and
these were combined into a single bias frame which was then applied to the object frames.
The images were flat-fielded using sky flats taken in each filter at the beginning and at the
end of each night. In the case of estimating the magnitudes for the structures throughout
the disk in NGC 3367, we have made careful analysis utilizing different IRAF tasks, in
particular, qphot and phot using different aperture diameters for bright stars in the field of
NGC 3367 in order to estimate the uncertainities in the final magnitudes at different filters
before estimating the final magnitudes reported for the different structures in NGC 3367.
The magnitudes reported here for the structures within NGC 3367 were estimated using an
aperture radius of 8 pixels (∼ 3′′.4 ∼ 715 pc).
Photometric calibration was achieved by nightly observations of standard stars of known
magnitudes from the “Dipper Asterism” M67 star cluster (Guilliland et al., 1991; Chevalier & Ilovaisky
1991). A total of 9 standard stars with a color interval −0.1 ≤ (B − V ) ≤ 1.4 and a similar
range in (V − I) were observed. The main extinction coefficients in B, V , R and I as well
as the color terms were calculated according to the following equations (Larsen 1999):
U − u0 = αU + βU(u− b)0
B − b0 = αB + βB(b− v)0
V − v0 = αV + βV (b− v)0
R− r0 = αR + βR(v − r)0
I − i0 = αI + βI(v − r)0
where B, V , R and I will be the estimated magnitudes, b, v, r and i are the instrumental
(and airmass-corrected) magnitudes. α and β are the transformation coefficients for each
filter.
In a first iteration, a constant value associated with the sky background was subtracted
from the images by using an interactive procedure that allows the user to select regions
on the frame free of galaxies and bright stars. Notice that uncertainities in determining
the sky background may be the dominant source of uncertainities in the estimation of the
magnitudes, color and surface brightness profiles.
The most energetic cosmic-ray events were automatically masked using the IRAF task
cosmicrays and field stars outside the bright visible disk of NGC 3367 were removed using
the IRAF task imedit when necessary. Within the galaxy itself, care was taken to identify
superposed stars. A final step in the basic reduction involved registration of all available
frames for each galaxy and in each filter to within ±0.1 pixel. This step was performed
by measuring centroids for foreground stars on the images and then performing geometric
transformations using IRAF tasks geomap and geotran.
All final images were convolved with a two dimensional gaussian function in such a way
as to have a similar final resolution equivalent to the largest one given by the V filter seeing,
that is, full width at half maximum, fwhm∼ 2′′.2.
– 5 –
2.1. Uncertainities in the Photometry
2.1.1. As a result of the Method
An estimation of the uncertainities in our photometry involves two parts: 1) The pro-
cedures to obtain instrumental magnitudes and 2) the uncertainty when such instrumental
magnitudes are transformed to a standard system. For 1), notice that the magnitudes pro-
duced at the output of the IRAF routines qphot and phot differ from each other as a result
of different methods used in those procedures. Since we also have applied extinction correc-
tions to the instrumental magnitudes in this step, our estimation of the uncertainities are
mainly concerned with these corrections and the estimation of the airmass. After a least
square fitting, the associated uncertainities to the slope for each principal extinction coeffi-
cient are; δ(kU) ∼ 0.038, δ(kB) ∼ 0.038, δ(kV ) ∼ 0.035, δ(kR) ∼ 0.025 and δ(kI) ∼ 0.025.
An additional uncertainity δ(airmass) ∼ 0.005 from the airmass routines in IRAF was also
considered.
For 2), the zero point and first order color terms are the most important to consider.
After transforming to the standard system, by adopting our best-fit coefficients, the formal
uncertainities from the assumed relations for α were 0.05, 0.05, 0.04, 0.04 and 0.04 in U ,
B, V , R and I and 0.04, 0.03, 0.03 and 0.04 for β. To estimate the total uncertainity
in each band, it is necessary to use the transformation equations and then propagate the
errors. Total typical uncertainties are 0.1, 0.1, 0.1, 0.09 and 0.1 in U , B, V , R and I bands,
respectively.
The estimated total magnitudes in this work were compared against other estimations
reported in the literature. This has been done for the standard stars and for NGC 3367 in
common with other works.
2.1.2. Standard Stars as calibrators
Our estimated CCD magnitudes for the nine stars in M67 are listed in Table 3 along with
magnitudes and cross reference identification numbers reported in the literature (Guilliland et al.,
1991; Chevalier & Ilovaisky 1991). A plot of our CCD estimated magnitudes versus those
reported by Guilliland et al., (1991) and Chevalier & Ilovaisky (1991) are shown in Figure
1 with no significant deviations, a continuous line with slope 1 is also plotted. These results
suggest, a σ ∼ 0.12, as the typical magnitude uncertainity. This is in agreement with our
prior uncertainity estimations.
– 6 –
Fig. 1.— Comparison between our estimated magnitudes and those from Gilliland et al.
(1991) [U , B, V and R bands] and Chevalier & Ilovaisky (1991) [I band] for 9 stars in
common taken as standards
3. Results
3.1. Total Magnitudes and Colors
In this study, we have estimated total magnitudes for U,B, V, R, I computed from differ-
ent circular apertures chosen interactively to assure that they are large enough to contain the
whole galaxy and still small enough to limit the uncertainities due to bad estimation of the
flux from the background and any field stars. Finally we chose an aperture with a diameter of
140′′ equivalent to 2′.33; this is slightly larger than the 2′.02 major diameter as given in NED.
There is, however, a foreground star within the disk of NGC 3367 which we did not remove
before estimating the global magnitudes and colors for NGC 3367. The star is object 82 in
Tables 7 and 9 and it lies about 29′′ to the north-west of the nucleus; we did not attempt to
remove it because it is surrounded with emission from stellar structures in the disk and thus
it makes it difficult to estimate the intensity level to replace the star with; star ID 82 turns
out to be a weak star with magnitudes U ∼ 17.9 B ∼ 17.9 V ∼ 17.4 R ∼ 16.9 I ∼ 16.2.
Total magnitudes from NGC 3367 were estimated in each band by using the phot routines
in IRAF. Our final estimated magnitudes for NGC 3367 were corrected for Galactic ex-
tinction (but not for intrinsic extinction); they are U = 11.70 ± 0.1, B = 11.91 ± 0.1,
V = 11.52 ± 0.1, R = 11.05 ± 0.1, and I = 10.43 ± 0.1. The colors of NGC 3367 are
U −B = −0.21, B − V = 0.39, B − I = 1.48.
– 7 –
Since the aperture to estimate the magnitudes for the stellar structures throughout
NGC 3367 must be small in order to include only star associations or small structures, it
was decided to use an aperture with radius 8 pixels equivalent to 3′′.41 ∼ 715 pc and use
IRAF task phot. One compared the estimated magnitudes, with an aperture of 8 pixels,
for the bright stars in the field south west of NGC 3367 with those listed in Table 5 (with
aperture radius of 26 pixels). The magnitude differences vary according to the star and
the filter. For star ID 86 the difference in empirical magnitudes are ∆U(8 − 26) = 0.07,
∆B(8 − 26) = 0.09, ∆V (8 − 26) = 0.10, ∆R(8 − 26) = 0.09, and ∆I(8 − 26) = 0.17; while
for star ID 91 the differences in magnitudes are ∆U(8 − 26) = 0.06, ∆B(8 − 26) = 0.08,
∆V (8 − 26) = 0.11, ∆R(8 − 26) = 0.10, and ∆I(8 − 26) = 0.18, fair is to say that the
magnitudes with aperture radius of 8 pixels have been corrected for Galactic extinction.
Magnitudes differences for each filter for both stars are similar indicating indeed that using
a smaller aperture radius gives an artificial weaker object by the amount given in each filter
but the differences are within the values for the uncertainities of our method. The estimated
magnitudes for the different structures throughout NGC 3367 (stellar associations) can be
taken as reliable and are listed in Table 6. Table 7 lists the estimated magnitudes for the
bright stars and a background galaxy in the field of NGC 3367. Table 8 lists the different
colors U −B, B− V and V − I for the stellar structures throughout NGC 3367, while table
9 lists the colors of the stars and the small galaxy in the field of NGC 3367. See Tables 6
for comments on individual objects.
Our estimated magnitudes for the whole galaxy in U , B, V and I bands and those
reported in the RC3 Catalogue (de Vaucouleurs et al., 1993) are in good agreement. The
Galactic extinction towards NGC 3367 in the different filters are: AU = 0.15, AB = 0.12,
AV = 0.09, AR = 0.08, and AI = 0.05 (Schlegel, Finbeiner & Davis 1998).
3.2. UBV RI Photometry of Star Associations and structures
It is a complicated problem to carry out photometry of stellar structures located within
the disk of a galaxy, partly because of the strongly varying background, and partly because
the structures are not perfect point sources (in other words, there must be a varying filling
factor) nor circles (as it was our aperture). For disk galaxies, the colors U − B, B − V ,
V − I are closely related to spectral type and show that there exist remarkable differences in
stellar content (Searle, Sargent & Bagnuolo 1973). The colors of structures in a given galaxy
are most certainly affected by internal reddening and chemical enrichment. In a particular
galaxy, as in our study, the colors of different structures would indicate the contributions
of the component stars in star clusters, very young star clusters embedded in HII region or
compact HII regions, stellar associations without gas, associations embedded in HII regions
and star clusters and associations with traces of emission [e.g. (Bica et al., 1996)].
It was decided in our photometric study of structures in NGC 3367 to estimate the
color magnitudes of different structures using IRAF task phot with an aperture with radius
8 pixels (3′′.4) which translates, in NGC 3367, to a radius with linear scale of 715 pc. No
aperture correction were applied to our estimated magnitudes of the different structures.
The photometry of all structures was obtained with the IRAF task phot which takes an area
of the sky, well off the extention of the disk of the galaxy in study, as a background to be
– 8 –
compared with.
In order to have an estimation of how good were our derived magnitudes for the stellar
structures throughout NGC 3367, we first estimated the magnitudes of bright field stars to
the south west of NGC 3367 (objets ID’s 85 and 90 in Table 7) utilizing two IRAF tasks,
qphot, and phot; each of these stars is relatively isolated and thus we could use apertures
with different radii in order to estimate their magnitudes in the five filters. Table 4 gives
our estimated magnitudes for the different filters for two bright stars in the south west
of the field of NGC 3367 utilizing IRAF task qphot using an aperture radius of 23 pixels,
equivalent to 9′′.80, and a width of ring (in order to estimate the brightness of the sky) of
pixels, equivalent to width of ring of 2′′.13. Additionally IRAF task phot was used with
three different circular apertures, one with a radius of 20 pixels, equivalent to 8′′.52, other
with radius 23 pixels, equivalent to 9′′.80 and another one with 26 pixels, equivalent to
11′′.08. The estimated magnitudes for the five filters, U , B, V , R, and I, are listed in Table
5. The largest uncertainity observed in Table 5 using three different apertures amounts to
∼ 0.05 mag in U , B, V , and R and it is ∼ 0.13 mag in I for both stars. Comparison
between estimated magnitudes using IRAF tasks qphot and phot for these field stars may
be estimated comparing the results listed in Tables 4 and 5. The difference amounts in the
worst case to 0.12 mag indicating that indeed IRAF task phot obtains a brighter value in
each filter with the largest aperture; however the difference in magnitudes using different
apertures with IRAF task phot is at worst ∼ 0.03 in the I filter between using an aperture’s
radius of 20 pixels and an aperture’s radius of 26 pixels.
The structures were chosen from the images in the I and U filters by eye at several loca-
tions of the disk of the galaxy with emphasis in choosing regions at different positions within
NGC 3367, for example: regions at larger distances than the bright south-west semicircle
(more than 10 kpc from the center, easily observed in images from the Palomar Sky Surveys),
from the stellar bar’s ends, from structures along and on spiral arms, from structures just
beyond the stellar bar, etc. in order to have enough of them as to be able to compare their
colors and estimate their ages. It included structures on the outside of the intense semicircle
structure with bright surface brightness to the west of the disk.
Table 6 lists the positions, α(J2000.0) and δ(J2000.0) 5 of the different structures
throughout NGC 3367, where we have estimated their magnitudes in the U,B, V, R and
I broadband filters corrected for Galactic extinction. Table 8 is similar to Table 6 and lists
the colors U−B, B−V , and V −I corrected for Galactic extinction of each stellar structure
in NGC 3367 along with their estimated SWB type.
We have estimated the colors of the area in front of the nucleus; the estimated mag-
nitudes were not corrected for intrinsic extinction; a visual extinction has been estimated,
from blue spectroscopy, to be only AV ∼ 0.9 Cid Fernandes et al. (2005). True magnitudes
must be brighter since it is known that there is a lot of molecular gas in the central region
of NGC 3367 (Garćıa-Barreto et al. 2005). At the distance of NGC 3367 (43.6 Mpc) the
absolute magnitude is MV = -13.24 taking into account the Galactic optical extinction. As
5The peak of the I image was anchored (in spatial position) to the peak of the high resolution ra-
dio continuum emission at 8.4 GHz (Garćıa-Barreto, Franco & Rudnick 2002) to the position α(J2000) =
10h 46m 34s.956 δ(J2000) = +13◦ 45′ 02′′.94. Although this is a logical supposition, it needs to be verified
since in other galaxies the peak of the radio continuum emission does not coincide with the compact optical
nucleus as a result of high extinction.
– 9 –
a comparison, the compact nucleus in the barred spiral galaxy NGC 4314, a LINER with a
circumnuclear structure (Garćıa-Barreto et al. 1991), has the following magnitude and col-
ors within an aperture of 6′′, 290 pc: V = 14.07, U −B = 0.51, and B−V = 1.11 (Benedict
1980), MV = -10.93 (at 10 Mpc taking into account the galactic optical extinction); the
compact nucleus of NGC 4314 is reported to have a blue magnitude of B = 16.6 mag per
square arc second (Lynds, Furenlid & Rubin 1973).
Figure 2 shows the U −B versus B − V color color diagram for the different structures
throughout the disk of NGC 3367. As a comparison, Figure 3, shows the corresponding U−B
versus B−V diagram for the Large Magellanic Cloud (Bica et al., 1996) stellar associations
embedded in HII regions (NA in the nomenclature of Bica et al.), star clusters (C), very young
clusters embedded in HII region or compact HII region (NC), stellar associations without
gas (A) and a supernovae remanent. Previuos U,B, V photometry of the SMC and LMC
star clusters indicated that young clusters in the SMC were concentrated along its bar, while
old clusters showed no concentration to the bar (van den Bergh 1981); while the young
clusters in the LMC were in and around the bar (van den Bergh 1981). The difference
between the color color diagrams between the clusters in the magellanic clouds and the
structures in NGC 3367 is noteworthy: the LMC has many very young clusters with colors
equivalent to the SWB 0 type (Searle, Wilkinson & Bagnuolo 1980; Bica, Claŕıa & Dottori
1992; Bica et al., 1996) 6 (see section on ages below) and might also be the result of filling
factor (radius of the aperture used, since the LMC is much closer than NGC 3367), intrinsic
extinction and different chemical enrichment in NGC 3367.
6The location of star clusters of different ages, in the U − B versus B − V color diagram delineate an
average sequence known as SWB 0 to SWB VII (Searle, Wilkinson & Bagnuolo 1980).
– 10 –
Fig. 2.— The color color diagram of different structures throughout NGC 3367 is shown.
Filled hexagon is the compact nucleus (ID 1), open squares are the bright star associations
embedded in HII regions to the west of the on the bright semicircle rim of the disk (ID 2 and
3), open hexagons are the bright stellar associations embedded in HII regions east of the end
of the bar (ID 4 - 6), filled squares are stellar associations to the northeast and southwest
of the bar (ID 37 and 38 respectively), asterisk is the region which includes supernovae
2003aa (ID 42), open triangles are stellar associations in the disk, filled triangles are stellar
associations beyond the semicircle bright end of the western side of the disk (ID 52 and 53).
SWB type (Searle, Wilkinson & Bagnuolo 1980; Bica et al., 1996), SWB 0 have estimated
ages between 0 and 107 yrs, SWB I between 107 and 3 × 107 yrs, SWB II between 3 × 107
and 7 × 107 yrs, SWB III between 7× 107 and 2 × 108 yrs, SWB IVA between 2× 108 and
4× 108 yrs, SWB IVB between 4× 108 and 8× 108 yrs, SWB V between 8× 108 and 2× 109
yrs, SWB VI between 2× 109 and 5× 109 yrs, and SWB VII between 5× 109 and 1.6× 1010
– 11 –
-0.5 0 0.5 1
SWB II
SWB III
SWB IVB 
SWB 0
SWB I
SWB IVA
SWB V
SWB VI
SWB VII
Fig. 3.— The color color diagram of different stellar associations in the Large Magellanic
Cloud (Bica et al., 1996) is shown as a comparison. In their nomenclature, open polygons
are stellar associations embedded in HII regions (NA, U−B in the interval from -1.1 to -0.55
and B−V in the interval -0.4 to 0.2), filled polygons are stellar associations without gas (A,
U − B in the interval from -0.9 to -0.5 and B − V in the interval -0.1 to 0.4), open squares
are very young clusters embedded in HII regions or compact HII regions (NC, U −B in the
interval from -1.05 to -0.3 and B − V in the interval -0.3 to 0.65), and open triangles are
star clusters (C, U −B in the interval from -0.95 to +0.5 and B − V in the interval -0.25 to
0.95) (Bica et al., 1996).
3.3. U B V R I Images
This section shows various images of NGC 3367. Figure 4 is the image in the U filter in a
grey scale and contours, proportional to surface brightness, showing the different structures
throughout NGC 3367.
– 12 –
Fig. 4.— Optical image, of NGC 3367, is shown in the broadband filter in the Ultraviolet
in greyscale and contours. Contours are in mag arcsec−2, and approximately correspond to
mU ∼ 23.6, 22.6, 21.8, 21.4, 21.1, 20.7, 20.4, 19.6, 18.8, 18.1, and 17.4.
– 13 –
77 78
131243
Right Ascension (J2000)10 46 40 36
Fig. 5.— North east quadrant of the U image showing with circles the positions of different
stellar structures; the circle is ∼ 6′′.8 in diameter which, at the distance of NGC 3367,
corresponds to a linear scale of 1.430 kpc.
– 14 –
      Right Ascension (J2000)
+13 45 00
Fig. 6.— As for Fig. 5 but showing the Southeast quadrant.
– 15 –
Right Ascension (J2000)
Fig. 7.— As for Fig. 5 but showing the Southwest quadrant.
– 16 –
Fig. 8.— As for Fig. 5 but showing the Northwest quadrant.
– 17 –
Figures 5, 6, 7, and 8 show the four different quadrants of NGC 3367 with a circle
indicating the position of the structure observed and its number, according to table 6, with
the circle having the diameter of the aperture utilized for the photometry, that is ∼ 6′′.8
which at the distance of NGC 3367 translates into a linear scale of ∼ 1.4 kpc. Figure 9
shows the I image of the galaxy with a larger area in order to indicate the field stars and
the background spiral galaxy. Figures 10, 11 and 12 show the U −B, B−V and V − I color
images of NGC 3367.
Fig. 9.— Optical image of NGC 3367 in the broadband I filter is shown in greyscale and
contours; contours are in mag arcsec−2 and approximately correspond to m∼20.2, 19.2, 18.7,
18.4, 18.2, and 18. Circles indicate the positions of the stars in the field of NGC 3367, except
for circle in the upper left corner that indicates the position of stellar structure ID 75; each
circle is 8 pixels in radius or ∼ 3′′.4. Stars 86 and 91 were used to estimate the uncertainities
in our photometry when using IRAF tasks qphot (with one aperture) and phot with three
different circular apertures. ID 90 is a background (disk) galaxy.
– 18 –
RIGHT ASCENSION (J2000)
10 46 40 38 36 34 32 30
13 46 15
45 45
44 45
Fig. 10.— U − B color image of the disk galaxy NGC 3367: Greyscale is in arbitrary units
in such a way that white areas indicate brighter ultraviolet emission.
– 19 –
RIGHT ASCENSION (J2000)
10 46 40 38 36 34 32 30
13 46 15
45 45
44 45
Fig. 11.— B − V color image of the disk galaxy NGC 3367.
– 20 –
RIGHT ASCENSION (J2000)
10 46 40 38 36 34 32 30
13 46 15
45 45
44 45
Fig. 12.— V − I color image of the disk galaxy NGC 3367.
4. Discussion
4.1. Spatial distribution of structures with different SWB type
There are 42 stellar structures with age type SWB I 7 out of 81 observed which cor-
respond to 51%. A natural question is, where is their spatial location? Structure ID 1
corresponds to the central innermost stellar association which includes the nucleus of the
galaxy; ID 2 and 3 are two stellar associations embedded in bright HII regions on the western
bright surface brightness edge of the disk at about 10 kpc from the center; ID 4 and 5 lie on
an inner eastern bright surface brightness area which seems to be a spiral arm or part of an
inner ring (just beyond the edge of the stellar bar) at about 4.5 kpc from the center; ID 6
7Approximate intervals of ages to different SWB classes are as follows (Searle, Wilkinson & Bagnuolo
1980; Bica et al., 1996): SWB 0 have ages between 0 and 107 yrs, SWB I have ages between 107 and 3×107
yrs, SWB II have agesbetween 3 × 107 and 7 × 107 yrs, SWB III have ages between 7 × 107 and 2 × 108
yrs, SWB IVAhave ages between 2× 108 and 4× 108 yrs, SWB IVB have ages between 4× 108 and 8× 108
yrs,SWB V have ages between 8×108 and 2×109 yrs, SWB VI have ages between 2×109 and 5×109yrs, and
SWB VII have ages between 5 × 109 and 1.6 × 1010 yrs (Chiosi, Bertelli & Bressan 1988; Girardi & Bica
1993; Anders & Fritze-v. Alvensleben 2003).
– 21 –
Fig. 13.— Histogram of number of structures studied in this work versus their B − V color.
Notice that 61 out of 81 of the structures have B − V color less than 0.5 (blue).
and 48 lie on another structure on an eastern spiral arm, parallel to the arm where ID 4 and
5 lie, at about 8 kpc from the center; ID 7 and 8 lie on the inner most spiral arm north-west
of the center; ID 14 lies on the crooked spiral arm north west of the center at about 6 kpc;
ID 18 lies at about 10 kpc east of the center just outside of the second spiral arm; ID 19 - 22,
25, 27 all lie on the southern spiral arm; ID 30 lies on a circular surface brightness structure
south-west of the south-west end of the stellar bar; ID 31 - 35 and 40 all lie on the western
spiral arm; ID 43 lies on an interarm on the eastern region of the disk at about 8.5 kpc; ID
57 lies on an interarm region west of the nucleus at about 8 kpc.
Structures ID’s 52 - 55, 58, 59, 62 - 74, and 80 lie outside the bright surface brightness
semicircle at distances more than about 13 kpc. The features are detected and shown in
Figs. 4, 5, 6, 7, and 8.
It is important to emphasize that in the central region (ID 1), the western sources
(ID 4 - 6) and the eastern sources (ID 2, 3), there is a large velocity dispersion of ionized
gas, detected through Hα (Garćıa-Barreto & Rosado 2001) and in the molecular gas CO
(Garćıa-Barreto et al. 2005).
In summary, most of the structures with age type SWB I lie close or on spiral arms.
Perhaps the most important result of the spatial distribution of structures with age type
SWB I is that several lie outside of the eastern bright surface brightness disk, ID 58 and 59
to the south, ID 65, 66, 69, 70, to the east while ID 53, 71 - 74 lie to the western side and ID
75 lies well outside the disk to the north-eastern end. The colors of structures ID 58, 59, 71 -
74 and 75 suggest that they are newly formed stellar structures and yet they lie at distances
beyond the bright visible disk of NGC 3367, that is beyond 10 kpc from the center.
– 22 –
4.2. Estimated ages of the structures throughout NGC 3367
It is difficult to speak about ages of the different structures throughout NGC 3367
mainly because, as we have seen, different structures could indicate star associations em-
bbeded in HII regions, very young star cluster embedded in HII regions, star associations
not associated with gas, star associations in or around the nucleus, and other combinations.
Among some of the problems with estimating the magnitudes of different structures are: fill-
ing factor, spatial distribution of structure within the aperture, and the fact that we used a
circular aperture. We realize that with our circular aperture diameter, of 6′′.8 ∼ 1.4 kpc, for
estimating magnitudes and colors one can not detect individual star clusters in this galaxy.
However, the study of star clusters with U,B, V, R, and I photometry and colors, and their
derived ages in the LMC (Searle, Sargent & Bagnuolo 1973; Searle, Wilkinson & Bagnuolo
1980) might be taken as an excellent reference to compare the U,B, V, R, and I colors of the
different structures throughout NGC 3367 and estimate their ages if only one were to assume
that the colors were equivalent, the chemical abundance were similar, have the same metal-
licity as in the LMC (which of course there is no reason to be an absolute valid assumption)
and more important we might use the SWB ages if one ignores the internal reddening.
ID 42, which includes supernova 2003AA, (asterisk in Figs. 2 and 4) has colors similar
to SWB II. Structures ID 52 and ID 53, beyond the bright western high surface brightness
rim of NGC 3367 (filled triangles in Fig. 2) have equivalent colors to clusters SWB IVB
and V. ID 37 and ID 38 are the structures north-east and south-west respectively of the
stellar bar (filled squares in Fig. 2) have colors similar to SWB VI, indicating old stellar
populations, but this result needs to be taken with caution since there the colors have not
been corrected for intrinsic extinction as a result of the probable existence of molecular gas
(CO, H2) and dust at least to the southwest side of the bar (Garćıa-Barreto et al. 2005).
Figure 12 shows the histogram of the number of structure throughout NGC 3367 versus
the color B − V where there is a large number of structures with blue colors, B − V ≤ 0.5.
Figure 13 shows the histogram of age groups according to SWB types (assuming that the
models for star clusters in the LMC also apply to the structures and angular resolution
observed in NGC 3367) where 64% of the structures observed have age types smaller or
equal than SWB type II or less than 70 Myrs.
Figs. 13 and 14 suggest that a large number of structures throughout NGC 3367 are
relatively blue and young structures. This number of young structures would probably
increase as one were able to somehow correct for intrinsic extinction, and different metallicity.
5. Conclusions
To conclude, we have obtained several images in the broadband filters U,B, V, R, and
I in order to estimate the optical magnitudes and colors of 81 different stellar structures
throughout the disk of NGC 3367. The structures were chosen from the images in the I and
U filters by eye at different locations of the disk of the galaxy in order to have enough of
them as to be able to compare their colors as a function of their spatial location. It included
structures to the north-east, south and west, well outside of the semicircle structure with
bright surface brightness.
Our estimated magnitudes for the NGC 3367, after correcting for Galactic extinction are
U = 11.70±0.1, B = 11.91±0.1,V = 11.52±0.1, R = 11.05±0.1, and I = 10.43±0.1. NGC
– 23 –
Fig. 14.— Histogram of number of structures studied in this work versus age group, SWB
type. Notice that 86% (70 out of 81) of the structures have SWB types I, II or III. This
number would increase as a result of intrinsic extinction.
3367 global colors, after being corrected for Galactic extinction are U−B = −0.21, B−V =
0.39, B−I = 1.48. All images except the image in V were convolved with an appropiate two
dimensional gaussian function in order to have a final of 2′′.2 full width at half maximum,
since the seeing was different for each filter and was about 1′′.7 to 2′′.2. The 81 stellar
structures reported in this paper were selected mainly from the U and the I images based on
the location in the disk in order to have as many as possible from different positions in NGC
3367. We have made careful analysis of the calibration methods to estimate magnitudes
and have compared different IRAF tasks, in particular, qphot and phot utilizing different
apertures in order to estimate the uncertainities in the final magnitudes at different filters
with 9 stars in M 67 as our standards. In the case of estimating the magnitudes for the
structures throughout the disk in NGC 3367, we have made careful analysis utilizing different
IRAF tasks, in particular, qphot and phot using different aperture diameters for the bright
stars in the field of NGC 3367 in order to estimate the uncertainities in the final magnitudes
at different filters before estimating the final magnitudes reported for the different structures
in NGC 3367. The magnitudes reported here for the structures in NGC 3367 were estimated
using an aperture radius of 8 pixels (∼ 3′′.4 ∼ 715 pc).
We were able to estimate the optical magnitudes U,B, V, R, and I and colors U−B, B−
V, U − V, and V − I for 81 different stellar structures throughout the disk in NGC 3367. It
is difficult to estimated the ages of the structures in NGC 3367 given our circular aperture
diameter, equivalent to 6′′.8 ∼ 1.4 kpc. However if their colors were taken as representative
as the colors of star clusters (studied by many other authors with better angular resolution,
– 24 –
appropiate chemical abundance and current theoretical star evolutionary tracks) in the LMC
many have colors equivalent to cluster types SWB I, and SWB II suggesting that many are
young associations with only tens of millions of years of age.
We found 41 structures out of 81 (50%) with age type SWB I. Several of those structures
lie near or in spiral arms; some lie outside of the bright surface brightness visible disk (for
example the POSS image).
In order to understand better the large scale environment of NGC 3367 it would also
be very important to determine the large scale spatial distribution and kinematics of atomic
hydrogen (HI) and new observations with high angular resolution of the emission of the
molecular gas (CO, H2) in the center of NGC 3367.
Acknowledgements
JAGB and HMHT thank the staff of the Observatorio Astronomico Nacional at San
Pedro Mártir, Baja California, México for the help in the observations. HMHT acknowl-
edges support from grant CONACyT (México) 42810. JAGB acknowledges partial financial
support from DGAPA (UNAM, México) grant IN107806-2. The authors would like to thank
the anonimous referee for his (her) comments and suggestions on how to improve this paper.
– 25 –
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This preprint was prepared with the AAS LATEX macros v5.2.
– 28 –
Table 1: General Properties of the barred disk galaxy NGC 3367
Characteristic Value Reference
Hubble Type (RC3) SB(rs)c 3
Nucleus spectral type Sy 2-like, HII 1,2
U mag 11.89 ± 0.15 3
B mag 12.05 ± 0.14 3
V mag 11.50 ± 0.14 3
I mag 10.60 ± 0.07 4
Vsys(HI) 3030 ± 8 km s
Vsys(opt) 2850 ± 50 km s
Vsys(FP
a) 3032 ± 3 km s−1 6
Vsys(CO) 3035 ± 5 km s
α(J2000) 10h 46m 34.95s 8
δ(J2000) +13◦ 46′ 02.9′′ 8
log LB/L⊙ 10.68 9
Photometric major axis P.A. 109◦ ± 4 10
Photometric inclination 6◦ ± 1 10
Major kinematic axis P.A. 51◦ ± 3 6
Inclination of disk (from kinematics) 30
Stellar bar P.A. 65◦ ± 5 11
Stellar bar diameter 32′′ ∼ 6.7 kpc 11
M(HI) 7× 109 M⊙ 5
M(H2), r=27
′′ 2.6× 109 M⊙ 7
M(H2), r=4
′′.5 5.9× 108 M⊙ 7
Visual extinction, Av/2 toward nucleus
b ∼ 75 mag 7
Total Radio Continuum (20 cm) flux density 119.5 mJy 12
Sum flux density (20 cm) from extended lobes 39 mJy 8
Projected distance of each synchrotron lobe ∼6 kpc 8
Position angle of inner radio continuum synchroton emission ∼ 46◦± 6 8
Position angle of synchrotron lobes ∼ 30◦ ± 20 8, 13
References: 1) Véron-Cetty & Véron (1986), 2) Ho, et al. (1997a), 3) de Vaucouleurs et al. (1993) RC3, 4) Nasa Extragalactic
Database (NED), 5) Huchtmeier & Seiradakis (1985), 6) Garćıa-Barreto & Rosado (2001), 7) Garćıa-Barreto et al. (2005), 8)
Garćıa-Barreto, Franco & Rudnick (2002), 9) Tully (1988), 10) Grosbøl (1985), 11) Garćıa-Barreto et al. (1996a,b), 12) Condon
et al. (1998), 13) Garćıa-Barreto et al. (1998)
a From Fabry-Perot Hα optical interferometry; b Maloney (1990).
– 29 –
Table 2: Journal of observations, average seeing and exposure time.
U B V R I
Seeing ∼ 2′′.0 ∼ 2′′.1 ∼ 2′′.2 ∼ 1′′.80 ∼ 1′′.70
∆λ (Å) 600 950 1400 400 1600
λcentralefective (Å) 3540 4330 5750 6340 8040
M67 8×30s 8×30s 8×15s 8×5s 8×5s
NGC 3367 5×600s 5×600s 5×600s 8×300s 8×300s
Table 3: Our estimated UBVRI photometry of stars in M67 with IRAF phot, and those
observed by other groups
Our ID ID1,2 U(ours) U1 B(ours) B1 V (ours) V 1 R(ours) R1 I(ours) I2
1 48,14c 13.79 13.76 13.75 13.74 13.17 13.16 12.84 12.84 12.50 12.49
2 16,15c 12.92 12.90 12.85 12.86 12.27 12.27 11.94 11.95 11.59 11.57
33 49,17c 13.85 13.84 13.80 13.78 13.21 13.20 12.88 12.86 12.53 12.50
4 28,18c 13.36 13.37 13.35 13.37 12.89 12.91 12.63 12.65 12.32 12.33
5 52,19 13.84 13.84 13.79 13.80 13.21 13.22 12.88 12.89 12.53 12.53
6 27,20c 13.37 13.40 13.35 13.35 12.78 12.78 12.46 12.46 12.10 12.12
7 13,21c 12.62 12.65 12.59 12.60 12.13 12.14 11.86 11.87 11.54 11.57
8 37,22c 13.68 13.70 13.41 13.43 12.61 12.63 12.16 12.17 11.72 11.74
9 44,23 13.69 13.72 13.66 13.65 13.09 13.09 12.77 12.77 12.42 12.43
1 (Guilliland et al., 1991); 2 (Chevalier & Ilovaisky 1991); 3 Position of star #3 is: α(B1950.0)=08h 48m 37s.5,
δ(B1950.0)=+11◦ 57′ 23′′.4; as a comparison, the position and magnitude reported in the USNO-B Star Catalog (Monet et al.
2003), for a star probably associated with star #3 is: α(B1950.0)=08h 48m 37s.95, δ(B1950.0)=+11◦ 57′ 57′′.9 magB1 = 13.98,
magB2 = 13.54
Table 4: UBVRI estimated photometry of bright stars in the field of NGC 3367 with IRAF
task qphot, aperture (apr), and width of ring (wor)
apr = 23 pixels (9′′.8), wor = 5′′
ID α(J2000.0) δ(J2000.0) U B V R I
85 10h 46m 27s.56 +13◦ 43′ 46′′.0 13.91 13.51 12.87 12.47 12.22
90 10h 46m 30s.60 +13◦ 42′ 28′′.6 13.13 13.00 12.68 12.37 12.12
– 30 –
Table 5: UBVRI Comparative Photometry of bright stars in the field of NGC 3367, using
IRAF task phot with three aperture (apr) radii: apr 20 pixels ∼ 8′′.5, 23 pixels ∼ 9′′.8 and
26 pixels ∼ 11′′.1
apr = 20 pixels (8′′.5)
ID α(J2000.0) δ(J2000.0) U B V R I
85 10h 46m 27s.56 +13◦ 43′ 46′′.0 13.87 13.46 12.82 12.43 12.12
90 10h 46m 30s.60 +13◦ 42′ 28′′.6 13.09 12.95 12.63 12.32 12.02
apr = 23 pixels (9′′.8)
85 10h 46m 27s.56 +13◦ 43′46′′.0 13.87 13.46 12.81 12.42 12.11
90 10h 46m 30s.60 +13◦ 42′28′′.6 13.09 12.95 12.62 12.31 12.01
apr = 26 pixels (11′′.1)
85 10h 46m 27s.56 +13◦ 43′46′′.0 13.86 13.45 12.81 12.42 12.09
90 10h 46m 30s.60 +13◦ 42′28′′.6 13.09 12.95 12.62 12.31 11.99
– 31 –
Table 6. UBV RI Photometry, corrected for Galactic extinction, of structures throughout
NGC 3367 using IRAF task phot using an aperture with radius 8 pixels ∼ 3′′.41 ∼ 715 pc
ID α(J2000.0) δ(J2000.0) U B V R I
11 34s.9492 45′ 02′′ .82 14.84 15.39 14.92 14.39 13.92
2 31s.71 45′ 00′′ .0 16.49 17.28 17.05 16.82 16.45
3 31s.70 44′ 54′′ .1 16.45 17.24 17.00 16.79 16.43
4 36s.62 45′ 09′′ .2 16.65 16.91 16.47 16.03 15.50
5 36s.45 45′ 05′′ .0 16.64 16.92 16.47 16.02 15.48
6 37s.46 45′ 11′′ .7 16.89 17.31 17.10 16.79 16.31
7 34s.66 45′ 16′′ .3 16.98 17.27 16.84 16.42 15.82
8 33s.96 45′ 10′′ .2 16.73 17.05 16.62 16.20 15.62
9 36s.62 45′ 18′′ .6 17.09 17.24 16.79 16.36 15.84
10 36s.44 45′ 15′′ .3 17.16 17.24 16.72 16.26 15.67
11 35s.68 45′ 22′′ .2 17.58 17.71 17.24 16.77 16.18
12 36s.10 45′ 28′′ .4 17.42 17.63 17.22 16.83 16.27
13 35s.73 45′ 28′′ .0 17.56 17.72 17.31 16.91 16.36
14 33s.40 45′ 20′′ .8 17.51 17.83 17.48 17.08 16.51
15 32s.84 45′ 13′′ .2 17.82 17.93 17.49 17.06 16.43
16 32s.29 45′ 05′′ .2 17.75 18.02 17.68 17.30 16.71
17 35s.67 44′ 39′′ .9 17.22 17.49 17.09 16.69 16.14
18 37s.91 45′ 03′′ .3 18.58 19.09 18.70 18.29 17.64
19 37s.47 44′ 29′′ .8 18.05 18.53 18.33 17.93 17.48
20 36s.47 44′ 26′′ .0 17.52 17.90 17.49 17.08 16.58
21 36s.02 44′ 27′′ .1 17.76 18.02 17.57 17.15 16.60
22 36s.03 44′ 24′′ .3 17.32 17.83 17.47 17.07 16.63
23 35s.20 44′ 23′′ .6 17.42 17.66 17.32 16.95 16.43
24 35s.30 44′ 23′′ .7 17.38 17.62 17.30 16.93 16.42
25 34s.17 44′ 25′′ .9 17.57 17.84 17.43 17.06 16.50
26 33s.71 44′ 26′′ .6 17.66 17.94 17.59 17.22 16.68
27 33s.42 44′ 38′′ .6 17.35 17.62 17.25 16.87 16.28
28 33s.40 44′ 44′′ .5 17.54 17.67 17.24 16.81 16.21
29 33s.31 44′ 48′′ .2 17.45 17.59 17.15 16.75 16.12
30 32s.84 44′ 45′′ .7 17.53 17.88 17.50 17.15 16.54
31 31s.68 45′ 07′′ .7 17.78 18.26 17.99 17.66 17.10
32 32s.06 45′ 20′′ .3 17.45 17.89 17.58 17.27 16.79
33 32s.16 45′ 22′′ .4 17.43 17.87 17.58 17.27 16.80
34 31s.93 45′ 24′′ .3 17.47 17.91 17.68 17.36 16.88
35 32s.02 45′ 30′′ .7 17.49 18.04 17.78 17.46 17.02
36 35s.45 45′ 14′′ .6 17.61 17.57 16.91 16.43 15.76
373 35s.68 45′ 06′′ .2 17.61 17.25 16.40 15.84 15.20
384 34s.15 45′ 00′′ .5 17.50 17.29 16.48 15.93 15.25
39 34s.69 45′ 50′′ .0 18.69 18.96 18.63 18.24 17.75
40 33s.63 45′ 51′′ .4 18.35 18.72 18.45 18.12 17.70
41 36s.32 45′ 42′′ .3 18.16 18.31 17.96 17.62 17.12
425 36s.74 45′ 32′′ .9 18.14 18.29 17.85 17.42 16.91
43 37s.03 45′ 28′′ .1 17.88 18.16 17.72 17.28 16.77
44 37s.39 45′ 35′′ .4 18.14 18.32 17.99 17.62 17.09
45 34s.42 45′ 31′′ .9 17.73 17.83 17.45 17.07 16.52
46 33s.23 45′ 26′′ .9 17.64 17.82 17.41 17.02 16.48
47 35s.01 44′ 47′′ .3 17.67 17.62 17.05 16.59 15.94
48 37s.02 44′ 59′′ .1 17.58 17.86 17.44 17.00 16.46
49 36s.37 44′ 48′′ .5 17.82 17.88 17.37 16.90 16.31
50 35s.62 44′ 49′′ .1 17.65 17.75 17.20 16.72 16.09
51 35s.82 44′ 54′′ .9 17.38 17.49 16.97 16.52 15.89
52 31s.03 44′ 49′′ .6 19.42 19.60 19.01 18.58 17.79
53 32s.06 44′ 31′′ .5 19.21 19.67 19.05 18.61 17.81
54 38s.19 44′ 38′′ .1 19.04 19.34 19.01 18.61 17.92
55 38s.32 44′ 44′′ .2 19.32 19.56 19.12 18.66 18.02
56 36s.95 44′ 37′′ .0 18.51 18.63 18.18 17.76 17.13
57 32s.44 44′ 47′′ .7 17.96 18.23 17.83 17.42 16.84
58 36s.22 44′ 09′′ .0 19.70 19.93 19.48 19.07 18.30
59 36s.60 44′ 10′′ .4 19.42 19.81 19.43 19.00 18.29
60 37s.12 45′ 44′′ .9 18.90 19.02 18.71 18.28 17.77
61 37s.55 45′ 44′′ .3 18.62 18.84 18.63 18.23 17.86
62 35s.56 46′ 04′′ .5 19.68 18.84 18.63 18.23 17.86
63 34s.39 46′ 04′′ .5 19.61 19.80 19.63 19.27 18.96
64 33s.87 46′ 06′′ .0 19.81 19.90 19.85 19.36 19.12
65 32s.70 45′ 53′′ .1 19.50 19.69 19.46 19.18 18.70
66 39s.05 44′ 52′′ .2 19.57 19.87 19.32 18.96 18.21
67 39s.39 45′ 04′′ .5 20.07 20.12 19.63 19.08 18.49
68 39s.47 45′ 08′′ .3 20.10 20.23 19.86 19.29 18.60
69 38s.72 45′ 01′′ .7 19.96 20.07 19.56 19.16 18.18
70 39s.10 44′ 53′′ .7 19.62 19.85 19.35 18.97 18.23
71 31s.10 44′ 18′′ .4 20.42 20.70 20.31 19.89 18.76
72 30s.98 44′ 13′′ .9 20.51 20.92 20.48 20.17 18.88
73 31s.07 44′ 07′′ .1 20.14 21.24 20.66 20.33 19.16
74 30s.30 45′ 19′′ .5 20.61 21.01 21.34 20.58 19.43
75 43s.42 46′ 10′′ .0 20.90 21.30 20.79 20.02 20.73
76 36s.69 45′ 08′′ .2 16.73 16.99 16.55 16.12 15.62
77 35s.94 45′ 10′′ .6 17.46 17.31 16.59 16.09 15.44
78 33s.99 44′ 46′′ .8 18.01 18.02 17.36 16.84 16.15
79 36s.44 45′ 38′′ .6 18.25 18.28 17.93 17.56 17.04
80 39s.07 45′ 05′′ .7 20.31 20.21 19.53 19.13 18.27
81 35s.07 45′ 21′′ .7 18.27 18.20 17.60 17.12 16.41
1Centermost region (nucleus + part of bulge) of the galaxy;
2Positions of peak of emission, in afilter where the intensity was strongest,
α(J2000.0)=10h 46m; δ(J2000.0)=+13◦ ;
3northeast region of the stellar bar;
4southwest region of the stellar bar;
– 32 –
5position of peak which includes supernova 2003AA type Ia (Swift, Pugh & Li
2003; Filippenko & Chornock 2003).
– 33 –
Table 7. UBV RI Photometry of stars and a background galaxy in the field of NGC 3367,
corrected for Galactic extinction, using IRAF task phot using an aperture with radius 8
pixels ∼ 3′′.41 ∼ 715 pc
ID α(J2000.0) δ(J2000.0) U B V R I
821 33s.10 45′ 11′′ .4 17.91 17.94 17.37 16.86 16.21
83 28s.56 45′ 54′′ .7 19.66 19.04 18.13 17.52 17.04
84 42s.53 44′ 33′′ .5 18.20 17.94 17.19 16.75 16.36
852 27s.56 43′ 46′′ .0 13.93 13.54 12.91 12.51 12.26
86 29s.34 44′ 12′′ .5 21.85 21.73 20.29 19.40 17.93
87 29s.78 43′ 27′′ .9 21.64 20.99 20.09 19.29 18.45
88 39s.28 44′ 08′′ .0 20.63 20.34 19.63 18.65 17.32
893 28s.62 42′ 41′′ .5 20.63 20.34 19.13 18.43 17.56
904 30s.60 42′ 28′′ .6 13.16 13.03 12.73 12.41 12.17
1dim star within NGC 3367;
2bright star south west in the field of NGC 3367; this star was taken as a test
star in order to estimate the uncertainities when obtaining its magnitudes with
different aperture radii;
3small galaxy with weak surface brightness to the south south west in the field
of NGC 3367;
4bright star south south west in the field of NGC 3367; this star was taken as
a test star in order to estimate the uncertainities when obtaining its magnitudes
with different aperture radii.
– 34 –
Table 8. U-B, B-V, V-I Colors of Stellar Structures in NGC 3367.
ID U − B B − V V − I SWB type1
12 -0.55 0.47 1.00 I
2 -0.79 0.23 0.60 I
3 -0.79 0.24 0.57 I
4 -0.26 0.44 0.97 I
5 -0.28 0.45 0.99 I
6 -0.42 0.21 0.79 I
7 -0.29 0.43 1.02 I
8 -0.32 0.43 1.00 I
9 -0.15 0.45 0.95 II
10 -0.08 0.52 1.05 III
11 -0.13 0.47 1.06 II
12 -0.21 0.41 0.95 II
13 -0.16 0.41 0.95 II
14 -0.32 0.35 0.97 I
15 -0.11 0.44 1.06 III
16 -0.27 0.34 0.97 I
17 -0.27 0.40 0.95 I
18 -0.51 0.39 1.05 I
19 -0.48 0.20 0.84 I
20 -0.38 0.41 0.91 I
21 -0.26 0.51 0.97 I
22 -0.51 0.36 0.84 I
23 -0.24 0.34 0.89 I
24 -0.24 0.32 0.88 I
25 -0.27 0.41 0.93 I
26 -0.28 0.35 0.91 I
27 -0.27 0.37 0.97 I
28 -0.13 0.43 1.03 II
29 -0.14 0.44 1.03 II
30 -0.35 0.38 0.96 I
31 -0.48 0.27 0.89 I
32 -0.44 0.31 0.79 I
33 -0.44 0.29 0.78 I
34 -0.44 0.23 0.80 I
35 -0.55 0.26 0.76 I
36 +0.04 0.66 1.15 VII
373 +0.36 0.85 1.20 VI
384 +0.21 0.81 1.23 VII
39 -0.27 0.33 0.88 I
40 -0.37 0.27 0.75 I
41 -0.15 0.35 0.84 II
425 -0.15 0.44 0.94 II
43 -0.28 0.44 0.95 I
44 -0.18 0.33 0.88 II
45 -0.10 0.38 0.93 III
46 -0.18 0.41 0.93 II
47 +0.05 0.57 1.11 IVB
48 -0.28 0.42 0.98 I
49 -0.06 0.51 1.06 IVA
50 -0.10 0.55 1.11 III
51 -0.11 0.52 1.08 III
52 -0.18 0.59 1.22 I
53 -0.44 0.60 1.24 I
54 -0.30 0.33 1.09 I
55 -0.24 0.44 1.10 I
56 -0.12 0.45 1.05 III
57 -0.27 0.40 0.99 I
58 -0.23 0.45 1.18 I
59 -0.39 0.38 1.14 I
60 -0.12 0.31 0.94 III
61 -0.22 0.21 0.77 II
62 -0.01 0.17 0.75 III
63 -0.19 0.17 0.67 II
64 -0.09 0.05 0.73 III
65 -0.19 0.23 0.76 II
66 -0.30 0.55 1.11 I
67 -0.05 0.49 1.14 IVA
68 -0.13 0.37 1.26 III
69 -0.11 0.51 1.38 III
70 -0.23 0.50 1.12 I
71 -0.28 0.38 1.55 I
72 -0.41 0.44 1.60 I
73 -1.10 0.58 1.50 I
74 -0.40 -0.33 1.91 II
75 -0.40 0.51 0.36 I
76 -0.26 0.44 0.94 I
77 +0.15 0.72 1.15 VII
78 -0.01 0.66 1.21 VII
79 -0.03 0.35 0.89 IVA
80 +0.10 0.68 1.26 VII
81 +0.07 0.60 1.19 IVB
1SWB type (Searle, Wilkinson & Bagnuolo
1980; Bica et al., 1996). Each type suggest an
approximate interval of age to different SWB
classes as follows: SWB 0 have ages between 0
and 107 yrs, SWB I have ages between 107 and
3×107 yrs, SWB II have ages between 3×107 and
7 × 107 yrs, SWB III have ages between 7 × 107
and 2 × 108 yrs, SWB IVA have ages between
2 × 108 and 4 × 108 yrs, SWB IVB have ages
– 35 –
between 4×108 and 8×108 yrs, SWB V have ages
between 8 × 108 and 2 × 109 yrs, SWB VI have
ages between 2 × 109 and 5 × 109 yrs, and SWB
VII have ages between 5 × 109 and 1.6 × 1010 yrs;
2Centermost region (nucleus + part of bulge) of
the galaxy;
3northeast region of the stellar bar;
4southwest region of the stellar bar;
5position of peak which includes supernova
2003AA type Ia Swift, Pugh & Li (2003);
Filippenko & Chornock (2003);
– 36 –
Table 9. UBVI Colors of foreground stars and a background galaxy in the field of NGC
3367.
ID U − B B − V V − I type1
822 -0.03 +0.57 1.16 F7V
83 +0.62 +0.91 1.09 K3V
84 +0.26 +0.75 0.83 G8V
853 +0.39 +0.63 0.65 G2III
86 -0.88 +1.44 2.36 K5III
87 +0.65 +0.90 1.64 G7III
88 +0.29 +0.71 2.31 K3III
894 +0.29 +1.21 1.57 spiral
905 +0.13 +0.30 0.56 F1III
1approximate spectral type
Mihalas & Binney (1981);
2dim star within NGC 3367;
3bright star south west in the field of NGC
3367; this star was taken as a test star in order
to estimate the uncertainities when obtaining
its magnitudes with different aperture radii;
4galaxy with weak surface brightness south
south west in the field of NGC 3367;
5bright star south south west in the field of
NGC 3367; this star was taken as a test star in
order to estimate the uncertainities when ob-
taining its magnitudes with different aperture
radii.
	Introduction
	Observations and Data Reduction
	Uncertainities in the Photometry
	As a result of the Method
	Standard Stars as calibrators
	Results
	Total Magnitudes and Colors
	U B V R I Photometry of Star Associations and structures
	U B V R I Images
	Discussion
	Spatial distribution of structures with different SWB type
	Estimated ages of the structures throughout NGC 3367
	Conclusions
