563 research outputs found
Charting the evolution of the ages and metallicities of massive galaxies since z=0.7
The stellar populations of intermediate-redshift galaxies can shed light onto
the growth of massive galaxies in the last 8 billion years. We perform deep,
multi-object rest-frame optical spectroscopy with IMACS/Magellan of ~70
galaxies in the E-CDFS with redshift 0.6522.7 and
stellar mass >10^{10}Msun. Following the Bayesian approach adopted for previous
low-redshift studies, we constrain the stellar mass, mean stellar age and
stellar metallicity of individual galaxies from stellar absorption features. We
characterize for the first time the dependence of stellar metallicity and age
on stellar mass at z~0.7 for all galaxies and for quiescent and star-forming
galaxies separately. These relations for the whole sample have a similar shape
as the z=0.1 SDSS analog, but are shifted by -0.28 dex in age and by -0.13 dex
in metallicity, at odds with simple passive evolution. We find that no
additional star formation and chemical enrichment are required for z=0.7
quiescent galaxies to evolve into the present-day quiescent population.
However, this must be accompanied by the quenching of a fraction of z=0.7
Mstar>10^{11}Msun star-forming galaxies with metallicities comparable to those
of quiescent galaxies, thus increasing the scatter in age without affecting the
metallicity distribution. However rapid quenching of the entire population of
massive star-forming galaxies at z=0.7 would be inconsistent with the
age/metallicity--mass relation for the population as a whole and with the
metallicity distribution of star-forming galaxies only, which are on average
0.12 dex less metal-rich than their local counterparts. This indicates chemical
enrichment until the present in at least a fraction of the z=0.7 massive
star-forming galaxies.[abridged]Comment: accepted for publication on ApJ, 26 pages, 13 figure
Assessing rem sleep behaviour disorder: From machine learning classification to the definition of a continuous dissociation index
Resolving the Stellar Outskirts of M31 and M33
Many clues about the galaxy assembly process lurk in the faint outer regions
of galaxies. The low surface brightnesses of these parts pose a significant
challenge for studies of diffuse light, and few robust constraints on galaxy
formation models have been derived to date from this technique. Our group has
pioneered the use of extremely wide-area star counts to quantitatively address
the large-scale structure and stellar content of external galaxies at very
faint light levels. We highlight here some results from our imaging and
spectroscopic surveys of M31 and M33.Comment: 6 pages, 4 figures. To appear in the proceedings of "Island Universes
- Structure and Evolution of Disk Galaxies", editor R.S. de Jong (Springer:
Dordrecht
The Pittsburgh Sloan Digital Sky Survey MgII Quasar Absorption-Line Survey Catalog
We present a catalog of intervening MgII quasar absorption-line systems in
the redshift interval 0.36 <= z <= 2.28. The catalog was built from Sloan
Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the
catalog contains > 17,000 measured MgII doublets. We also present data on the
~44,600 quasar spectra which were searched to construct the catalog, including
redshift and magnitude information, continuum-normalized spectra, and
corresponding arrays of redshift-dependent minimum rest equivalent widths
detectable at our confidence threshold. The catalog is available on the web. A
careful second search of 500 random spectra indicated that, for every 100
spectra searched, approximately one significant MgII system was accidentally
rejected. Current plans to expand the catalog beyond DR4 quasars are discussed.
Many MgII absorbers are known to be associated with galaxies. Therefore, the
combination of large size and well understood statistics makes this catalog
ideal for precision studies of the low-ionization and neutral gas regions
associated with galaxies at low to moderate redshift. An analysis of the
statistics of MgII absorbers using this catalog will be presented in a
subsequent paper.Comment: AJ, in pres
Direct detection of galaxy stellar halos : NGC 3957 as a test case
We present a direct detection of the stellar halo of the edge-on S0 galaxy
NGC 3957, using ultra-deep VLT/VIMOS V and R images. This is achieved with a
sky subtraction strategy based on infrared techniques. These observations allow
us to reach unprecedented high signal-to-noise ratios up to 15 kpc away from
the galaxy center, rendering photon-noise negligible. The 1 sigma detection
limits are R = 30.6 mag/arcsec^2 and V = 31.4 mag/arcsec^2. We conduct a
thorough analysis of the possible sources of systematic errors that could
affect the data: flat-fielding, differences in CCD responses, scaling of the
sky background, the extended halo itself, and PSF wings. We conclude that the
V-R colour of the NGC 3957 halo, calculated between 5 and 8 kpc above the disc
plane where the systematic errors are modest, is consistent with an old and
preferentially metal-poor normal stellar population, like that revealed in
nearby galaxy halos from studies of their resolved stellar content. We do not
find support for the extremely red colours found in earlier studies of diffuse
halo emission, which we suggest might have been due to residual systematic
errors.Comment: Accepted for publication in A&A - "language edited
The Intergalactic Stellar Population from Mergers of Elliptical Galaxies with Dark Matter halos
We present simulations of dry-merger encounters between pairs of elliptical
galaxies with dark matter halos. The aim of these simulations is to study the
intergalactic stellar populations produced in both parabolic and hyperbolic
encounters. We model progenitor galaxies with total-to-luminous mass ratios
M_T/M_L 3 and 11. The initial mass of the colliding galaxies are chosen so that
M_1/M_2 and 10. The model galaxies are populated by particles representing
stars, as in Stanghellini et al. (2006), and dark matter. Merger remnants
resulting from these encounters display a population of unbounded particles,
both dark and luminous. The number of particles becoming unbounded depends on
orbital configuration, with hyperbolic encounters producing a larger luminous
intracluster population than parabolic encounters. Furthermore, in simulations
with identical orbital parameters, a lower M_T/M_L of the colliding galaxies
produces a larger fraction of unbounded luminous particles. For each modeled
collision, the fraction of unbounded to initial stellar mass is the same in all
mass-bins considered, similarly to what we found previously by modeling
encounters of galaxies without dark halos. The fraction of intergalactic to
total luminosity resulting from our simulations is ~ 4% and ~ 6% for
dark-to-bright mass rations of 10 and 2 respectively. These unbounded-to-total
luminous fractions are down from 17 % that we had previously found in the case
of no dark halos. Our results are in broad agreement with intergalactic light
observed in groups of galaxies, while the results of our previous models
without dark halos better encompass observed intracluster populations. We
suggest a possible formation scenario of intergalactic stars.Comment: Accepted for publication in Ap
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