30 research outputs found
Young Star Clusters in the Dwarf Irregular Galaxy, UGC 7636, Interacting with the Giant Elliptical Galaxy NGC 4472
We present integrated Washington CT1 photometry of 18 bright blue objects
discovered in the dwarf galaxy UGC 7636 which is located 5'.5 southeast of the
giant elliptical galaxy NGC 4472, the brightest galaxy in the Virgo cluster.
Several lines of evidence indicate that UGC 7636 is interacting violently with
NGC 4472. These objects are very blue with colors of -0.4 < (C-T1) < 0.6, and
their magnitudes are in the range of 20.6 < T1 < 22.9 mag which corresponds to
absolute magnitudes of -10.6 < M(T1) < -8.3 mag for a distance modulus of
(m-M)o = 31.2. These objects are grouped spatially in three regions: the
central region of UGC 7636, the tidal tail region, and the HI cloud region. No
such objects were found in the counter tail region. It is concluded that these
objects are probably young star clusters which formed < 0.1Gyr ago during the
interaction between UGC 7636 and NGC 4472. Surface photometry of UGC 7636 (r <
83") shows that there is a significant excess of blue light along the tidal
tail region compared with other regions. The star clusters are bluer than the
stellar light in the tidal tail region, indicating that these clusters might
have formed later than most stars in the tidal tail region which were formed
later than most stars in the main body of the galaxy.Comment: 18 pages (AASLaTeX), 6 Postscript figures, Accepted for publication
in the Astronomical Journal, Nov. 30th, 199
Wide Field CCD Surface Photometry of the Giant Elliptical Galaxy NGC 4472 in the Virgo Cluster
We present deep wide field (16'.4 x 16'.4) Washington CT1 CCD surface
photometry of the giant elliptical galaxy NGC 4472, the brightest member in the
Virgo cluster. Our data cover a wider field than any previous CCD photometry as
well as going deeper. Surface brightness profiles of NGC 4472 are not well fit
by a single King model, but they can be fit approximately by two King models:
with separate models for the inner and outer regions. Surface brightness
profiles for the outer region can also be fit approximately by a deVaucouleurs
law. There is clearly a negative color gradient within 3' of NGC 4472, in the
sense that the color gets bluer with increasing radius. The slope of the color
gradient for this region is derived to be = -0.08 mag
arcsec for , which corresponds to a metallicity
gradient of [Fe/H] dex. However, the surface color gets
redder slowly with increasing radius beyond 3'. A comparison of the structural
parameters of NGC 4472 in C and T1 images has shown that there is little
difference in the ellipse shapes between isochromes and isophotes. In addition,
photometric and structural parameters of NGC 4472 have been determined.Comment: 8 pages(mnrasLaTeX), 8 Postscript figures, Accepted for publication
in MNRAS, 2000
Comparative study between N-body and Fokker-Planck simulations for rotating star clusters: I. Equal-mass system
We have carried out N-body simulations for rotating star clusters with equal
mass and compared the results with Fokker-Planck models. These two different
approaches are found to produce fairly similar results, although there are some
differences with regard to the detailed aspects. We confirmed the acceleration
of the core collapse of a cluster due to an initial non-zero angular momentum
and found a similar evolutionary trend in the central density and velocity
dispersion in both simulations. The degree of acceleration depends on the
initial angular momentum. Angular momentum is being lost from the cluster due
to the evaporation of stars with a large angular momentum on a relaxation time
scale.Comment: 11 pages, 13 eps figures, accepted for the publication of MNRA
The Globular Cluster System in the Inner Region of the Giant Elliptical Galaxy NGC 4472
We present a study of globular clusters in the inner region of the giant
elliptical galaxy NGC 4472, based on the HST WFPC2 archive data. We have found
about 1560 globular cluster candidates at the galactocentric radius r < 4
arcmin. V-(V-I) diagram of these objects shows a dominant vertical structure
which consists obviously of two components: blue globular clusters (BGCs) and
red globular clusters (RGCs). The luminosity function of the globular clusters
is derived to have a peak at V(max)=23.50+/-0.16 from Gaussian fitting. The
distance to NGC 4472 is estimated to be d=14.7+/-1.3 Mpc.The peak luminosity
for the RGCs is similar to that for the BGCs, which indicates that the RGCs may
be several Gyrs younger than the BGCs. The mean luminosity of the bright BGCs
decreases by 0.2 mag with increasing galactocentric radius over the range of 9
arcmin, while that of the RGCs does not. The observed color distribution of
these globular clusters is distinctively bimodal with peaks at (V-I) = 0.98 and
1.23. The mean observed color of all the globular clusters with V < 23.9 mag is
derived to be (V-I)=1.11. These colors are exactly the same as those for the
globular clusters in M87. It is found that the relative number of the BGCs to
the RGCs is increasing with the increasing galactocentric radius. Surface
number density profiles of both the BGCs and RGCs get flat in the central
region, and the core radii of the globular cluster systems are measured to be
r_c = 1.9 arcmin for the BGCs, r_c = 1.2 arcmin for the RGCs, and r_c = 1.3
arcmin for the total sample, which are much larger than the stellar core of the
galaxy. In general the properties of the globular clusters in the inner region
of NGC 4472 are consistent with those of the globular clusters in the outer
region of NGC 4472.Comment: 27 pages (AASLaTex), 22 Postscript Figures, Accepted for Publication
in the Astronomical Journal, Jul. 31st, 200
Dynamical evolution of rotating stellar systems - II. Post-collapse, equal mass system
We present the first post core collapse models of initially rotating star
clusters, using the numerical solution of an orbit-averaged 2D Fokker-Planck
equation. Based on the code developed by Einsel & Spurzem (1999), we have
improved the speed and the stability and included the steady three-body binary
heating source. We have confirmed that rotating clusters, whether they are in a
tidal field or not, evolve significantly faster than non-rotating ones.
Consequences for observed shapes, density distribution, and kinematic
properties of young and old star clusters are discussed. The results are
compared with gaseous and 1D Fokker-Planck models in the non-rotating case.Comment: 12 pages (MNLaTeX), 17 Postscript figures, Submitted to MNRA
X-ray Tail in NGC 7619
We present new observational results of NGC 7619, an elliptical galaxy with a
prominent X-ray tail and a dominant member of the Pegasus group. With Chandra
and XMM-Newton observations, we confirm the presence of a long X-ray tail in
the SW direction; moreover, we identify for the first time a sharp
discontinuity of the X-ray surface brightness in the opposite (NE) side of the
galaxy. The density, temperature and pressure jump at the NE discontinuity
suggest a Mach number ~1, corresponding to a galaxy velocity of ~500 km s-1,
relative to the surrounding hot gas. Spectral analysis of these data shows that
the Iron abundance of the hot gaseous medium is much higher (1-2 solar) near
the center of NGC 7619 and in the tail extending from the core than in the
surrounding regions (< 1/2 solar), indicating that the gas in the tail is
originated from the galaxy. The possible origin of the head-tail structure is
either on-going ram-pressure stripping or sloshing. The morphology of the
structure is more in line with a ram pressure stripping phenomenon, while the
position of NGC 7619 at the center of the Pegasus I group, and its dominance,
would prefer sloshing.Comment: ApJ accepted to appear in the 2008 December 1 issue; Added discussion
on sloshin
Reddening and Distance of the Local Group Starburst Galaxy IC 10
We estimate the reddening and distance of the nearest starburst galaxy IC 10
using deep near infrared photometry obtained with the Multi-Object
InfraRed Camera and Spectrograph (MOIRCS) on the Subaru telescope. We estimate
the foreground reddening toward IC 10 using photometry of IC 10 from the
Local Group Survey, obtaining mag. We derive the total
reddening including the internal reddening, mag, using
photometry of early-type stars in IC 10 and comparing
photometry of red giant branch stars in IC 10 and the SMC. Using the 2MASS
point source catalog of 20 Galactic globular clusters, we derive a relation
between the metallicity [Fe/H] and the slope of the red giant branch
in the color-magnitude diagram. The mean metallicity of the
red giant branch stars in IC 10 is estimated to be
[Fe/H]. The magnitude of the tip of the red giant branch
(TRGB) of IC 10 in the band is measured to be
. Based on the TRGB method, we estimate the distance
modulus of IC 10 to be , corresponding to the distance of kpc. This
confirms that IC 10 is a member of the Local Group.Comment: 35 pages, 11 figures, To appear in the Astrophysical Journal, 200