1,435 research outputs found
The Red Sequence Luminosity Function in Massive Intermediate Redshift Galaxy Clusters
We measure the rest-frame B-band luminosity function of red-sequence galaxies
(RSLF) of five intermediate-redshift (0.5 950
km/s) clusters. Cluster galaxies are identified through photometric redshifts
based on imaging in seven bands (five broad, and two narrow) using the WIYN
3.5m telescope. The luminosity functions are well-fit down to M_B^*+3 for all
of the clusters out to a radius of R_200. For comparison, the luminosity
functions for a sample of 59 low redshift clusters selected from the SDSS are
measured as well. There is a brightening trend (M_B^* increases by 0.7 mags by
z=0.75) with redshift comparable to what is seen in the field for similarly
defined galaxies, although there is a hint that the cluster red-sequence
brightening is more rapid in the past (z>0.5), and relatively shallow at more
recent times. Contrary to other claims, we find little evidence for evolution
of the faint end slope. Previous indications of evolution may be due to
limitations in measurement technique, bias in the sample selection, and cluster
to cluster variation. As seen in both the low and high redshift sample, a
significant amount of variation in luminosity functions parameters alpha and
M^* exists between individual clusters.Comment: 40 pages, 14 figures, accepted for publication in the Astrophysical
Journa
Evolution of the Red Sequence Giant to Dwarf Ratio in Galaxy Clusters out to z ~ 0.5
We analyze deep g' and r' band data of 97 galaxy clusters imaged with MegaCam
on the Canada-France-Hawaii telescope. We compute the number of luminous
(giant) and faint (dwarf) galaxies using criteria based on the definitions of
de Lucia et al. (2007). Due to excellent image quality and uniformity of the
data and analysis, we probe the giant-to-dwarf ratio (GDR) out to z ~ 0.55.
With X-ray temperature (Tx) information for the majority of our clusters, we
constrain, for the first time, the Tx-corrected giant and dwarf evolution
separately. Our measurements support an evolving GDR over the redshift range
0.05 < z < 0.55. We show that modifying the (g'-r'), m_r' and K-correction used
to define dwarf and giant selection do not alter the conclusion regarding the
presence of evolution. We parameterize the GDR evolution using a linear
function of redshift (GDR = alpha * z + beta) with a best fit slope of alpha =
0.88 +/- 0.15 and normalization beta = 0.44 +/- 0.03. Contrary to claims of a
large intrinsic scatter, we find that the GDR data can be fully accounted for
using observational errors alone. Consistently, we find no evidence for a
correlation between GDR and cluster mass (via Tx or weak lensing). Lastly, the
data suggest that the evolution of the GDR at z < 0.2 is driven primarily by
dry merging of the massive giant galaxies, which when considered with previous
results at higher redshift, suggests a change in the dominant mechanism that
mediates the GDR.Comment: 20 pages, 15 figures. Accepted to MNRA
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Generation of a three-dimensional collagen scaffold-based model of the human endometrium.
The endometrium is the secretory lining of the uterus that undergoes dynamic changes throughout the menstrual cycle in preparation for implantation and a pregnancy. Recently, endometrial organoids (EO) were established to study the glandular epithelium. We have built upon this advance and developed a multi-cellular model containing both endometrial stromal and epithelial cells. We use porous collagen scaffolds produced with controlled lyophilization to direct cellular organization, integrating organoids with primary isolates of stromal cells. The internal pore structure of the scaffold was optimized for stromal cell culture in a systematic study, finding an optimal average pore size of 101 ”m. EO seeded organize to form a luminal-like epithelial layer, on the surface of the scaffold. The cells polarize with their apical surface carrying microvilli and cilia that face the pore cavities and their basal surface attaching to the scaffold with the formation of extracellular matrix proteins. Both cell types are hormone responsive on the scaffold, with hormone stimulation resulting in epithelial differentiation and stromal decidualization
The origin of the mu_e - M_B and Kormendy relations in dwarf elliptical galaxies
The present work is aimed at studying the distribution of galaxies of
different types and luminosities along different structural scaling relations
to see whether massive and dwarf ellipticals have been shaped by the same
formation process. This exercise is here done by comparing the distribution of
Virgo cluster massive and dwarf ellipticals and star forming galaxies along the
B band effective surface brightness and effective radius vs. absolute magnitude
relations and the Kormendy relation to the predictions of models tracing the
effects of ram-pressure stripping on disc galaxies entering the cluster
environment and galaxy harassment. Dwarf ellipticals might have been formed
from low luminosity, late-type spirals that recently entered into the cluster
and lost their gas because of a ram-pressure stripping event, stopping their
activity of star formation. The perturbations induced by the abrupt decrease of
the star formation activity are sufficient to modify the structural properties
of disc galaxies into those of dwarf ellipticals. Galaxy harassment induce a
truncation of the disc and generally an increase of the effective surface
brightness of the perturbed galaxies. The lack of dynamical simulations of
perturbed galaxies spanning a wide range in luminosity prevents us to drive any
firm conclusion on a possible harassment-induced origin of the low surface
brightness dwarf elliptical galaxy population inhabiting the Virgo cluster.
Although the observed scaling relations are consistent with the idea that the
distribution of elliptical galaxies along the mentioned scaling relation is
just due to a gradual variation with luminosity of the Sersic index n, the
comparison with models indicates that dwarf ellipticals might have been formed
by a totally different process than giant ellipticalsComment: Accepted for publication on A&
New improved Moser-Trudinger inequalities and singular Liouville equations on compact surfaces
We consider a singular Liouville equation on a compact surface, arising from
the study of Chern-Simons vortices in a self dual regime. Using new improved
versions of the Moser-Trudinger inequalities (whose main feature is to be
scaling invariant) and a variational scheme, we prove new existence results.Comment: to appear in GAF
Galaxy evolution by color-log(n) type since redshift unity in the Hubble Ultra Deep Field
We explore the use of the color-log(n) plane (where n is the global Sersic
index) as a tool for subdividing the high redshift galaxy population in a
physically-motivated manner. Using a series of volume-limited samples out to
z=1.5 in the Hubble Ultra Deep Field (UDF) we confirm the correlation between
color-log(n) plane position and visual morphology observed locally and in other
high redshift studies in the color and/or structure domain. Via comparison to a
low redshift sample from the Millennium Galaxy Catalogue we quantify evolution
by color-log(n) type, accounting separately for the specific selection and
measurement biases against each. Specifically, we measure decreases in B-band
surface brightness of 1.57 +/- 0.22 mag/sq.arcsec and 1.65 +/- 0.22
mag/sq.arcsec for `blue, diffuse' and `red, compact' galaxies respectively
between redshift unity and the present day.Comment: 12 pages, 6 figures, to be published in A&A (accepted 29/10/08
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&
Star formation activities in early-type brightest cluster galaxies
We identify a total of 120 early-type Brightest Cluster Galaxies (BCGs) at
0.1<z<0.4 in two recent large cluster catalogues selected from the Sloan
Digital Sky Survey (SDSS). They are selected with strong emission lines in
their optical spectra, with both H{\alpha} and [O II]{\lambda}3727 line
emission, which indicates significant ongoing star formation. They constitute
about ~ 0.5% of the largest, optically-selected, low-redshift BCG sample, and
the fraction is a strong function of cluster richness. Their star formation
history can be well described by a recent minor and short starburst
superimposed on an old stellar component, with the recent episode of star
formation contributing on average only less than 1 percent of the total stellar
mass. We show that the more massive star-forming BCGs in richer clusters tend
to have higher star formation rate (SFR) and specific SFR (SFR per unit galaxy
stellar mass). We also compare their statistical properties with a control
sample selected from X-ray luminous clusters, and show that the fraction of
star-forming BCGs in X-ray luminous clusters is almost one order of magnitude
larger than that in optically-selected clusters. BCGs with star formation in
cooling flow clusters usually have very flat optical spectra and show the most
active star formation, which may be connected with cooling flows.Comment: 15 pages, 10 figures and 2 tables, accepted for publication in MNRA
Cluster galaxies in XMMU J2235-2557: galaxy population properties in most massive environments at z~1.4
We present a multi-wavelength study of galaxy populations in the core of the
massive, X-ray luminous cluster XMMU J2235 at z=1.39, based on VLT and HST
optical and near-infrared photometry. Luminosity functions in the z, H, and Ks
bands show a faint-end slope consistent with being flat, and a characteristic
magnitude M* close to passive evolution predictions of M* of local massive
clusters, with a formation redshift z>2. The color-magnitude and color-mass
diagrams show evidence of a tight red sequence of massive galaxies, with
overall old stellar populations, generally early-type morphology, typically
showing early-type spectral features and rest-frame far-UV emission consistent
with very low star formation rates (SFR<0.2Msun/yr). Star forming spectroscopic
members, with SFRs of up to ~100Msun/yr, are all located at clustercentric
distances >~250kpc, with the central cluster region already appearing
effectively quenched. Massive galaxies in the core of this cluster appear to be
in an advanced evolutionary stage in terms of both star formation and mass
assembly. The high-mass end of the galaxy stellar mass function is essentially
already in place, and the stellar mass fraction estimated within r500 (~1%,
Kroupa IMF) is already similar to that of local massive clusters. On the other
hand, morphological analysis of the massive red sequence galaxies suggests that
they are smaller than similarly massive local early-types. While possibly
affected by systematics and biases, this result might imply that, in spite of
the overall early assembly of these sources, their evolution is not complete,
and processes like minor (and likely dry) merging might still shape their
structural properties to resemble those of their local counterparts, without
substantially affecting their stellar mass or host stellar
populations.[abridged]Comment: 14 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
The chemical enrichment of long gamma-ray bursts nurseries up to z = 2
Aims. We investigate the existence of a metallicity threshold for the production of long gamma-ray bursts (LGRBs). Methods. We used the host galaxies of the Swift/BAT6 sample of LGRBs. We considered the stellar mass, star formation rate (SFR), and metallicity determined from the host galaxy photometry and spectroscopy up to z = 2 and used them to compare the distribution of host galaxies to that of field galaxies in the mass-metallicity and fundamental metallicity relation plane. Results. We find that although LGRBs also form in galaxies with relatively large stellar masses, the large majority of host galaxies have metallicities below log(O=H) ⌠8:6. The extension to z = 2 results in a good sampling of stellar masses also above Log(M=M) ⌠9:5 and provides evidence that LGRB host galaxies do not follow the fundamental metallicity relation. As shown by the comparison with dedicated numerical simulations of LGRB host galaxy population, these results are naturally explained by the existence of a mild (âŒ0:7 Z) threshold for the LGRB formation. The present statistics does not allow us to discriminate between different shapes of the metallicity cutoff, but the relatively high metallicity threshold found in this work is somewhat in disagreement to most of the standard single-star models for LGRB progenitors. © ESO, 201
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