118 research outputs found
The Globular Cluster Populations of Giant Galaxies: Mosaic Imaging of Five Moderate-Luminosity Early-Type Galaxies
This paper presents results from wide-field imaging of the globular cluster
(GC) systems of five intermediate-luminosity (M_V ~-21 to -22) early-type
galaxies. The aim is to accurately quantify the global properties of the GC
systems by measuring them out to large radii. We obtained BVR imaging of four
lenticular galaxies (NGC 5866, NGC 4762, NGC 4754, NGC 3384) and one elliptical
galaxy (NGC 5813) using the KPNO 4m telescope and MOSAIC imager and traced the
GC population to projected galactocentric radii ranging from ~20 kpc to 120
kpc. We combine our imaging with Hubble Space Telescope data to measure the GC
surface density close to the galaxy center. We calculate the total number of
GCs (N_GC) from the integrated radial profile and find N_GC = 340 +/- 80 for
NGC 5866, N_GC = 2900 +/- 400 for NGC 5813, N_GC = 270 +/- 30 for NGC 4762,
N_GC = 115 +/- 15$ for NGC 4754, and N_GC = 120 +/- 30 for NGC 3384. The
measured GC specific frequencies are S_N between 0.6 and 3.6 and T in the range
0.9 to 4.2. These values are consistent with the mean specific frequencies for
the galaxies' morphological types found by our survey and other published data.
Three galaxies (NGC 5866, NGC 5813, NGC 4762) had sufficient numbers of GC
candidates to investigate color bimodality and color gradients in the GC
systems. NGC 5813 shows strong evidence (>3 sigma) for bimodality and a B-R
color gradient resulting from a more centrally concentrated red (metal-rich) GC
subpopulation. We find no evidence for statistically significant color
gradients in the other two galaxies.Comment: 61 pages, 21 figures, 11 tables. Accepted for publication in The
Astronomical Journa
The Globular Cluster System of the Spiral Galaxy NGC7814
We present the results of a wide-field photometric study of the globular
cluster (GC) system of the edge-on Sab spiral NGC7814. This is the first spiral
to be fully analyzed from our survey of the GC systems of a large sample of
galaxies beyond the Local Group. NGC7814 is of particular interest because a
previous study estimated that it has 500-1000 GCs, giving it the largest
specific frequency (S_N) known for a spiral. Understanding this galaxy's GC
system is important in terms of our understanding of the GC populations of
spirals in general and has implications for the formation of massive galaxies.
We observed the galaxy in BVR filters with the WIYN 3.5-m telescope, and used
image classification and three-color photometry to select GC candidates. We
also analyzed archival HST WFPC2 images of NGC7814, both to help quantify the
contamination level of the WIYN GC candidate list and to detect GCs in the
inner part of the galaxy halo. Combining HST data with high-quality
ground-based images allows us to trace the entire radial extent of this
galaxy's GC system and determine the total number of GCs directly through
observation. We find that rather than being an especially high-S_N spiral,
NGC7814 has <200 GCs and S_N ~ 1, making it comparable to the two most
well-studied spirals, the Milky Way and M31. We explore the implications of
these results for models of the formation of galaxies and their GC systems. The
initial results from our survey suggest that the GC systems of typical
ellipticals can be accounted for by the merger of two or more spirals, but that
for highly-luminous ellipticals, additional physical processes may be needed.Comment: 28 pages, incl. 4 figures; accepted for publication in The
Astronomical Journal, November 2003 issu
The Globular Cluster Population of NGC 7457: Clues to the Evolution of Field S0 Galaxies
In this paper we present the results of a wide-field imaging study of the
globular cluster (GC) system of the field S0 galaxy NGC 7457. To derive the
global properties of the GC system, we obtained deep BVR images with the WIYN
3.5 m telescope and Minimosaic Imager and studied the GC population of NGC 7457
to a projected radius of approximately 30 kpc. Our ground-based data were
combined with archival and published Hubble Space Telescope data to probe the
properties of the GC system close to the galaxy center and reduce contamination
in the GC candidate sample from foreground stars and background galaxies. We
performed surface photometry of NGC 7457 and compared the galaxy's surface
brightness profile with the surface density profile of the GC system. The
profiles have similar shapes in the inner 1 arcminute (3.9 kpc), but the GC
system profile appears to flatten relative to the galaxy light at larger radii.
The GC system of NGC 7457 is noticeably elliptical in our images; we measure an
ellipticity of 0.66 +/- 0.14 for the GC distribution, which is consistent with
our measured ellipticity of the galaxy light. We integrated the radial surface
density profile of the GC system to derive a total number of GCs N_GC = 210 +/-
30. The GC specific frequency normalized by the galaxy luminosity and mass are
S_N = 3.1 +/- 0.7 and T = 4.8 +/- 1.1, respectively. Comparing the derived GC
system properties and other empirical data for NGC 7457 to S0 formation
scenarios suggests that this field S0 galaxy may have formed in an unequal-mass
merger.Comment: 40 pages, 10 figures, accepted for publication in The Astrophysical
Journa
WIYN Imaging of the Globular Cluster Systems of the Spiral Galaxies NGC891 and NGC4013
We present results from a WIYN 3.5m telescope imaging study of the globular
cluster (GC) systems of the edge-on spiral galaxies NGC891 and NGC4013. We used
the 10' x 10' Minimosaic Imager to observe the galaxies in BVR filters to
projected radii of ~20 kpc from the galaxy centers. We combined the WIYN data
with archival and published data from WFPC2 and ACS on the Hubble Space
Telescope to assess the contamination level of the WIYN GC candidate sample and
to follow the GC systems further in toward the galaxies' centers. We
constructed radial distributions for the GC systems using both the WIYN and HST
data. The GC systems of NGC891 and NGC4013 extend to 9+/-3 kpc and 14+/-5 kpc,
respectively, before falling off to undetectable levels in our images. We use
the radial distributions to calculate global values for the total number (N_GC)
and specific frequencies (S_N and T) of GCs. NGC4013 has N_GC = 140+/-20, S_N =
1.0+/-0.2 and T = 1.9+/-0.5; our N_GC value is ~40% smaller than a previous
determination from the literature. The HST data were especially useful for
NGC891, because the GC system is concentrated toward the plane of the galaxy
and was only weakly detected in our WIYN images. Although NGC891 is thought to
resemble the Milky Way in its overall properties, it has only half as many GCs,
with N_GC = 70+/-20, S_N = 0.3+/-0.1 and T = 0.6+/-0.3. We also calculate the
galaxy-mass-normalized number of blue (metal-poor) GCs in NGC891 and NGC4013
and find that they fall along a general trend of increasing specific frequency
of blue GCs with increasing galaxy mass. Given currently available resources,
the optimal method for studying the global properties of extragalactic GC
systems is to combine HST data with wide-field, ground-based imaging with good
resolution. The results here demonstrate the advantage gained by using both
methods when possible.Comment: 43 pages, 11 figures 6 tables; accepted to The Astronomical Journal.
Online AJ version at http://iopscience.iop.org/1538-3881/140/2/430
Global Properties of the Globular Cluster Systems of Four Spiral Galaxies
We present results from a wide-field imaging study of the globular cluster
(GC) systems of a sample of edge-on, Sb-Sc spiral galaxies ~7-20 Mpc away. This
study is part of a larger survey of the ensemble properties of the GC
populations of giant galaxies. We imaged the galaxies in BVR filters with
large-format CCD detectors on the WIYN 3.5-m telescope, to projected radii of
~20-40 kpc. For four galaxies (NGC 2683, NGC 3556, NGC 4157, and NGC 7331), we
quantify the radial distributions of the GC systems and estimate the total
number, luminosity- and mass-normalized specific frequencies (S_N and T), and
blue (metal-poor) fraction of GCs. A fifth galaxy (NGC 3044) was apparently too
distant for us to have detected its GC system. Our S_N for NGC 2683 is 2.5
times smaller than the previously-published value, likely due in part to
reduced contamination from non-GCs. For the spiral galaxies analyzed for the
survey to date, the average number of GCs is 170+/-40 and the weighted mean
values of S_N and T are 0.8+/-0.2 and 1.4+/-0.3. We use the survey data to
derive a relationship between radial exent of the GC system and host galaxy
mass over a factor of 20 in mass. Finally, we confirm the trend, identified in
previous survey papers, of increasing specific frequency of metal-poor GCs with
increasing galaxy mass. We compare the data with predictions from a simple
model and show that carefully quantifying the numbers of metal-poor GCs in
galaxies can constrain the formation redshifts of the GCs and their host
galaxies.Comment: 30 pages, including 14 figures and 13 tables; accepted for
publication in The Astronomical Journal, Oct 2007 issu
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