28 research outputs found
RXJ0152.7-1357: Stellar populations in an X-ray luminous galaxy cluster at z=0.83
We present a study of the stellar populations of galaxies in the cluster
RXJ0152.7-1357 at a redshift of 0.83. The study is based on new high S/N
spectroscopy of 29 cluster members covering the wavelength range 5000-10000A as
well as r'i'z' photometry of the cluster. The scaling relations between
velocity dispersions, luminosities and Balmer line strengths appear to be in
agreement with pure passive evolution of the stellar populations with a
formation redshift z=4. However, the strengths of the D4000 indices and the
metal indices do not support this interpretation. Compared to z=0, the metal
indices (C4668, Fe4383, CN3883, G4300 and CN2) show that at least half of the
non-emission line galaxies in RXJ0152.7-1357 have [alpha/Fe] of 0.2 dex higher,
and about half of the galaxies have significantly lower metal content. The
differences in stellar populations of the galaxies are associated with the
location of the galaxies relative to the X-ray emission. The galaxies with weak
C4668 and G4300, as well as galaxies with weak [OII] emission, are located in
areas of low X-ray luminosity. It is possible that these galaxies are
experiencing the effect of the cluster merger taking place in RXJ0152.7-1357 as
(short) episodes of star formation, while the galaxies in the cores of the
X-ray sub-clumps are unaffected by the merger. The spectroscopy of the
RXJ0152.7-1357 galaxies shows for the first time galaxies in a rich cluster at
intermediate redshift that cannot evolve passively into the present day galaxy
population in rich clusters. Additional physical processes may be at work and
we speculate that merging with infalling (disk) galaxies in which stars have
formed over an extended period might produce the required reduction in
[alpha/Fe]. (abridged)Comment: Accepted for publication in Astronomical Journal, 39 pages, uses
emulateapj.cls, 18 figures. High resolution color figures available by e-mail
request to the first autho
G2C2 II: Integrated colour-metallicity relations for Galactic Globular Clusters in SDSS passbands
We use our integrated SDSS photometry for 96 globular clusters in and
, as well as and photometry for a subset of 56 clusters, to derive
the integrated colour-metallicity relation (CMR) for Galactic globular
clusters. We compare this relation to previous work, including extragalactic
clusters, and examine the influence of age, present-day mass function
variations, structural parameters and the morphology of the horizontal branch
on the relation. Moreover, we scrutinise the scatter introduced by foreground
extinction (including differential reddening) and show that the scatter in the
colour-metallicity relation can be significantly reduced combining two
reddening laws from the literature. In all CMRs we find some low-reddening
young GCs that are offset to the CMR. Most of these outliers are associated
with the Sagittarius system. Simulations show that this is due less to age than
to a different enrichment history. Finally, we introduce colour-metallicity
relations based on the infrared Calcium triplet, which are clearly non-linear
when compared to and colours.Comment: Accepted for publication in MNRAS. 17 pages, 18 figure
The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment
The fraction of stellar mass contained in globular clusters (GCs), also
measured by number as the specific frequency, is a fundamental quantity that
reflects both a galaxy's early star formation and its entire merging history.
We present specific frequencies, luminosities, and mass fractions for the
globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster
Survey, the largest homogeneous catalog of its kind. We find that 1) GC mass
fractions can be high in both giants and dwarfs, but are universally low in
galaxies with intermediate luminosities. 2) The behavior of specific frequency
across galaxy mass is dominated by the blue GCs. 3) The GC fractions of
low-mass galaxies exhibit a dependence on environment. Nearly all dwarf
galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87,
presenting the first strong evidence that GC formation in dwarfs is biased
toward dense environments. 4) GC formation in central dwarfs is biased because
their stars form earliest and most intensely. Comparisons to the Millennium
Simulation show that central dwarfs have older stellar populations and form
more stars at higher star formation rates (SFRs) and SFR surface densities. The
SFR surface density in simulated dwarfs peaks before the total SFR, naturally
producing GC populations that are older and more metal-poor than the field
stars. 5) Dwarfs within ~40 kpc of the giant ellipticals M87 and M49 are red
and have few or no GCs, suggesting that they have been tidally stripped and
have contributed their GCs to the halos of their giant neighbors. The central
dwarfs with high GC mass fractions are thus likely to be the survivors most
similar to the protogalaxies that assembled the rich M87 globular cluster
system.(Abridged)Comment: 27 pages, 21 figures, 7 tables. Accepted for publication in the
Astrophysical Journa
A Gemini/GMOS Study of Intermediate Luminosity Early-Type Virgo Cluster Galaxies. I. Globular Cluster and Stellar Kinematics
We present a kinematic analysis of the globular cluster systems and diffuse
stellar light of four intermediate luminosity (sub-) early-type
galaxies in the Virgo cluster based on Gemini/GMOS data. Our galaxy sample is
fainter () than most previous studies, nearly doubling the
number of galaxies in this magnitude range that now have GC kinematics. The
data for the diffuse light extends to , and the data for the globular
clusters reaches 8--. We find that the kinematics in these outer regions
are all different despite the fact that these four galaxies have similar
photometric properties, and are uniformly classified as "fast rotators" from
their stellar kinematics within . The globular cluster systems exhibit a
wide range of kinematic morphology. The rotation axis and amplitude can change
between the inner and outer regions, including a case of counter-rotation. This
difference shows the importance of wide-field kinematic studies, and shows that
stellar and GC kinematics can change significantly as one moves beyond the
inner regions of galaxies. Moreover, the kinematics of the globular cluster
systems can differ from that of the stars, suggesting that the formation of the
two populations are also distinct.Comment: 24 pages, 21 figures, 9 table, ApJ in pres
Adaptive Optics Imaging of a Massive Galaxy Associated with a Metal-rich Absorber
The damped and sub-damped Lyman-alpha absorption line systems in quasar
spectra are believed to be produced by intervening galaxies. However, the
connection of quasar absorbers to galaxies is not well-understood, since
attempts to image the absorbing galaxies have often failed. While most DLAs
appear to be metal-poor, a population of metal-rich absorbers, mostly sub-DLAs,
has been discovered in recent studies. Here we report high-resolution K-band
imaging with the Keck Laser Guide Star Adaptive Optics (LGSAO) system of the
field of quasar SDSSJ1323-0021 in search of the galaxy producing the z = 0.72
sub-DLA absorber. With a metallicity of 2-4 times the solar level, this
absorber is of the most metal-rich systems found to date. Our data show a large
bright galaxy with an angular separation of only 1.25" from the quasar,
well-resolved from the quasar at the high resolution of our data. The galaxy
has a magnitude of K = 17.6-17.9, which corresponds to a luminosity of ~ 3-6
L*. Morphologically, the galaxy is fit with a model with an effective radius,
enclosing half the total light, of R_e = 4 kpc and a bulge-to-total ratio of
0.4-1.0, indicating a substantial bulge stellar population. Based on the
mass-metallicity relation of nearby galaxies, the absorber galaxy appears to
have a stellar mass > 10^{11} M_sun. Given the small impact parameter, this
massive galaxy appears to be responsible for the metal-rich sub-DLA. The
absorber galaxy is consistent with the metallicity-luminosity relation observed
for nearby galaxies, but is near the upper end of metallicity. Our study marks
the first application of LGSAO for study of structure of galaxies producing
distant quasar absorbers. Finally, this study offers the first example of a
massive galaxy with a substantial bulge producing a metal-rich absorber.Comment: 17 pages, 4 figures, 1 table; Accepted for publication in The
Astronomical Journa
G2C2 I: Homogeneous SDSS photometry for Galactic GCs
We present and aperture photometry for 96 Galactic
Globular Clusters, making this the largest homogeneous catalog of photometry
for these objects in the SDSS filter system. For a subset of 56 clusters we
also provide photometry in and . We carry out comparisons
with previous photometry as well as with the SDSS dataset. The data will be
useful for a series of applications in Galactic and extragalactic astrophysics.
Future papers will analyse the colour-metallicity relation, colour-magnitude
diagrams, and structural parameters. The compilation of results based on this
dataset will be collected in the Galactic Globular Cluster Catalog (G2C2).Comment: Accepted for publication in MNRAS. 12 pages, 6 figure
The Robo-AO-2 facility for rapid visible/near-infrared AO imaging and the demonstration of hybrid techniques
We are building a next-generation laser adaptive optics system, Robo-AO-2,
for the UH 2.2-m telescope that will deliver robotic, diffraction-limited
observations at visible and near-infrared wavelengths in unprecedented numbers.
The superior Maunakea observing site, expanded spectral range and rapid
response to high-priority events represent a significant advance over the
prototype. Robo-AO-2 will include a new reconfigurable natural guide star
sensor for exquisite wavefront correction on bright targets and the
demonstration of potentially transformative hybrid AO techniques that promise
to extend the faintness limit on current and future exoplanet adaptive optics
systems.Comment: 15 page