20 research outputs found
The Rich Globular Cluster System of Abell 1689 and the Radial Dependence of the Globular Cluster Formation Efficiency
We study the rich globular cluster (GC) system in the center of the massive
cluster of galaxies Abell 1689 (z=0.18), one of the most powerful gravitational
lenses known. With 28 HST/ACS orbits in the F814W bandpass, we reach magnitude
I_814=29 with >90% completeness and sample the brightest ~5% of the GC system.
Assuming the well-known Gaussian form of the GC luminosity function (GCLF), we
estimate a total population of N(GC_total) = 162,850 GCs within a projected
radius of 400kpc. As many as half may comprise an intracluster component. Even
with the sizable uncertainties, which mainly result from the uncertain GCLF
parameters, this is by far the largest GC system studied to date. The specific
frequency S_N is high, but not uncommon for central galaxies in massive
clusters, rising from S_N~5 near the center to ~12 at large radii. Passive
galaxy fading would increase S_N by ~20% at z=0. We construct the radial mass
profiles of the GCs, stars, intracluster gas, and lensing-derived total mass,
and we compare the mass fractions as a function of radius. The estimated mass
in GCs, M(GC_total)=3.9x10^10 Msun, is comparable to ~80% of the total stellar
mass of the Milky Way. The shape of the GC mass profile appears intermediate
between those of the stellar light and total cluster mass. Despite the extreme
nature of this system, the ratios of the GC mass to the baryonic and total
masses, and thus the GC formation efficiency, are typical of those in other
rich clusters when comparing at the same physical radii. The GC formation
efficiency is not constant, but varies with radius, in a manner that appears
similar for different clusters; we speculate on the reasons for this similarity
in profile.Comment: 13 pages, 11 figures; accepted for publication in Ap
AGB Connection and Ultraviolet Luminosity Excess in Elliptical Galaxies
Relying on infrared surface brightness fluctuactions to trace AGB properties
in a sample of elliptical galaxies in the Virgo and Fornax clusters, we assess
the puzzling origin of the "UV-upturn" phenomenon, recently traced down to the
presence of a hot horizontal branch stellar component. We find that the
UV-upturn actually signals a profound change in the c-m diagram of stellar
populations in elliptical galaxies, involving both the hot stellar component
and red-giant evolution.Comment: 13 pages & 13 figures -- To appear in the Astrophysical Journal (Sep
'08 issue). Further info on SBF models at
http://www.bo.astro.it/~eps/home.htm
The Hubble Deep Field South Flanking Fields
As part of the Hubble Deep Field South program, a set of shorter 2-orbit
observations were obtained of the area adjacent to the deep fields. The WFPC2
flanking fields cover a contiguous solid angle of 48 square arcminutes.
Parallel observations with the STIS and NICMOS instruments produce a patchwork
of additional fields with optical and near-infrared (1.6 micron) response.
Deeper parallel exposures with WFPC2 and NICMOS were obtained when STIS
observed the NICMOS deep field. These deeper fields are offset from the rest,
and an extended low surface brightness object is visible in the deeper WFPC2
flanking field. In this data paper, which serves as an archival record of the
project, we discuss the observations and data reduction, and present SExtractor
source catalogs and number counts derived from the data. Number counts are
broadly consistent with previous surveys from both ground and space. Among
other things, these flanking field observations are useful for defining slit
masks for spectroscopic follow-up over a wider area around the deep fields, for
studying large-scale structure that extends beyond the deep fields, for future
supernova searches, and for number counts and morphological studies, but their
ultimate utility will be defined by the astronomical community.Comment: 46 pages, 15 figures. Images and full catalogs available via the
HDF-S at http://www.stsci.edu/ftp/science/hdfsouth/hdfs.html at present. The
paper is accepted for the February 2003 Astronomical Journal. Full versions
of the catalogs will also be available on-line from AJ after publicatio
Globular cluster systems in fossil groups: NGC6482, NGC1132 and ESO306-017
We study the globular cluster (GC) systems in three representative fossil
group galaxies: the nearest (NGC6482), the prototype (NGC1132) and the most
massive known to date (ESO306-017). This is the first systematic study of GC
systems in fossil groups. Using data obtained with the Hubble Space Telescope
Advanced Camera for Surveys in the F475W and F850LP filters, we determine the
GC color and magnitude distributions, surface number density profiles, and
specific frequencies. In all three systems, the GC color distribution is
bimodal, the GCs are spatially more extended than the starlight, and the red
population is more concentrated than the blue. The specific frequencies seem to
scale with the optical luminosities of the central galaxy and span a range
similar to that of the normal bright elliptical galaxies in rich environments.
We also analyze the galaxy surface brightness distributions to look for
deviations from the best-fit S\'ersic profiles; we find evidence of recent
dynamical interaction in all three fossil group galaxies. Using X-ray data from
the literature, we find that luminosity and metallicity appear to correlate
with the number of GCs and their mean color, respectively. Interestingly,
although NGC6482 has the lowest mass and luminosity in our sample, its GC
system has the reddest mean color, and the surrounding X-ray gas has the
highest metallicity.Comment: 16 pages, 13 figures. Accepted for publication in A&
Near-IR Surface Brightness Fluctuations and Optical Colours of Magellanic Star Clusters
This work continues our efforts to calibrate model surface brightness
luminosities for the study of unresolved stellar populations, through the
comparison with data of Magellanic Cloud star clusters. We present here the
relation between absolute K_s-band fluctuation magnitude and (V - I) integrated
colour, using data from the 2MASS and DENIS surveys, and from the literature.
We compare the star cluster sample with the sample of early-type galaxies and
spiral bulges studied by Liu et al. (2002). We find that intermediate-age to
old clusters lie along a linear correlation with the same slope, within the
errors, of that defined by the galaxies in the barM_{K_s} vs. (V - I) diagram.
While the calibration by Liu et al. was determined in the colour range 1.05 <
(V - I_c)_0 = barM_{K_s} >= -9, 0.3 <=
(V - I) <= 1.25. This implies, according to Bruzual & Charlot (2003) and
Mouhcine & Lancon (2003) models, that the star clusters and the latest star
formation bursts in the galaxies and bulges constitute an age sequence. At the
same time, there is a slight offset between the galaxies and the star clusters
[the latter are ~ 0.7 mag fainter than the former at a given value of (V - I)],
caused by the difference in metallicity of roughly a factor of two. The
confrontation between models and galaxy data also suggests that galaxies with
K_s fluctuation magnitudes that are brighter than predicted, given their (V -
I) colour, might be explained in part by longer lifetimes of TP-AGB stars.
(Abridged version.)Comment: 13 pages, LaTeX, 5 figures, MNRAS, in pres
Globular cluster systems and galaxy formation
Globular clusters are compact, gravitationally bound systems of up to a
million stars. The GCs in the Milky Way contain some of the oldest stars known,
and provide important clues to the early formation and continuing evolution of
our Galaxy. More generally, GCs are associated with galaxies of all types and
masses, from low-mass dwarf galaxies to the most massive early-type galaxies
which lie in the centres of massive galaxy clusters. GC systems show several
properties which connect tightly with properties of their host galaxies. For
example, the total mass of GCs in a system scales linearly with the dark matter
halo mass of its host galaxy. Numerical simulations are at the point of being
able to resolve globular cluster formation within a cosmological framework.
Therefore, GCs link a range of scales, from the physics of star formation in
turbulent gas clouds, to the large-scale properties of galaxies and their dark
matter. In this Chapter we review some of the basic observational approaches
for GC systems, some of their key observational properties, and describe how
GCs provide important clues to the formation of their parent galaxies.Comment: 32 pages, 6 figures. Accepted for publication in the book "Reviews in
Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds
Kabath, Jones and Skarka; publisher Springer Nature) funded by the European
Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul"
2017-1-CZ01-KA203-03556
THE GOULD’S BELT DISTANCES SURVEY (GOBELINS). I. TRIGONOMETRIC PARALLAX DISTANCES AND DEPTH OF THE OPHIUCHUS COMPLEX
A Novel Method to Automatically Detect and Measure the Ages of Star Clusters in Nearby Galaxies: Application to the Large Magellanic Cloud
We present our new, fully automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia et al., estimates the ages of the clusters. Comparisons of our estimates with those from other surveys show the superiority of our method to extract and measure the ages of star clusters, even in the most crowded fields. An application of our method is shown for the high-resolution, multiband imaging of the Large Magellanic Cloud. We detect 4850 clusters in the 7 deg(2) we surveyed, 3451 of which have not been reported before. Our findings suggest multiple epochs of star cluster formation, with the most probable occurring similar to 310 Myr ago. Several of these events are consistent with the epochs of the interactions among the Large and Small Magellanic Clouds, and the Galaxy, as predicted by N-body numerical simulations. Finally, the spatially resolved star cluster formation history may suggest an inside-out cluster formation scenario throughout the LMC, for the past 1 Gyr.CONACyT Research Fellowships program; CONACyT [252364]; CONICYT; Programa de Astronomia/PCI; FONDO ALMA [31140024]; UNAM [PAPIIT IG100115]; DGAPA, UNAM; GA CR [14-21373S]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]