99 research outputs found
On the Continuous Formation of Field Spheroidal Galaxies in Hierarchical Models of Structure Formation
We re-examine the assembly history of field spheroidals as a potentially
powerful discriminant of galaxy formation models. Whereas monolithic collapse
and hierarchical, merger-driven, models suggest radically different histories
for these galaxies, neither the theoretical predictions nor the observational
data for field galaxies have been sufficiently reliable for precise conclusions
to be drawn. A major difficulty in interpreting the observations, reviewed
here, concerns the taxonomic definition of spheroidals in merger-based models.
Using quantitative measures of recent star formation activity drawn from the
internal properties of a sample of distant field galaxies in the Hubble Deep
Fields, we undertake a new analysis to assess the continuous formation of
spheroidal galaxies. Whereas abundances and redshift distributions of modelled
spheroidals are fairly insensitive to their formation path, we demonstrate that
the distribution and amount of blue light arising from recent mergers provides
a more sensitive approach. With the limited resolved data currently available,
the rate of mass assembly implied by the observed colour inhomogeneities is
compared to that expected in popular Lambda-dominated cold dark matter models
of structure formation. These models produce as many highly inhomogeneous
spheroidals as observed, but underpredict the proportion of homogeneous,
passive objects. We conclude that colour inhomogeneities, particularly when
combined with spectroscopic diagnostics for large, representative samples of
field spheroidals, will be a more valuable test of their physical assembly
history than basic source counts and redshift distributions. Securing such data
should be a high priority for the Advanced Camera for Surveys on Hubble Space
Telescope.Comment: 14 pages, 7 figures, submitted to MNRA
Unveiling the oldest and most massive galaxies at very high redshift
(Abridged) This work explores the existence of high redshift massive galaxies
unveiled with Spitzer+IRAC, but missed by conventional selection techniques
based on optical and near-infrared observations. To this end, we use the
multi-wavelength imaging data available for the GOODS-South field, and select a
flux-limited sample from the IRAC 3.6um image to m(AB)<23.26. We confine our
study to the galaxies undetected by the optical HST+ACS imaging and close to
the detection limit of the K-band image (K>23.5 AB). Our selection unveiled 20
galaxies on which we performed a detailed photometric analysis. For each
galaxy, we built an SED based on optical-to-8um photometry to estimate the
photo-z and to derive the main galaxies physical properties. The majority of
the sample sources show degenerate/bimodal solutions for the photometric
redshifts (Abridged). These can either be heavily dust-enshrouded (Av~2-4)
starbursts at 210^12 Lsun, or massive
post-starburst galaxies in the redshift interval 4<z<9 with stellar masses of
10^11 Msun. One galaxy, the only source in our sample with both an X-ray and a
24um detection, might be an extremely massive object at z~8 detected during a
post-starburst phase with concomitant QSO activity (although a lower-z solution
is not excluded). Our investigation of Spitzer-selected galaxies with very red
SEDs and completely undetected in the optical reveals a potential population of
massive galaxies at z>4 which appear to include significant AGN emissions.
These sources may be the oldest stellar systems at z~4. These, previously
unrecognized, optically obscured objects might provide an important
contribution to the massive-end (M>10^11 sun) of the high-z stellar mass
function and they would almost double it (Abridged).Comment: Accepted for publication in Astronomy and Astrophysic
Cosmic Star Formation: Constraints on the Galaxy Formation Models
We study the evolution of the cosmic star formation by computing the
luminosity density (LD) in the UV, B, J, and K bands, and the stellar mass
density (MD) of galaxies in two reference models of galaxy evolution: the pure
luminosity evolution (PLE) model developed by Calura & Matteucci (2003) and the
semi-analytical model (SAM) of hierarchical galaxy formation by Menci et al.
(2002). The former includes a detailed description of the chemical evolution of
galaxies of different morphological types with no density evolution; the latter
includes the merging histories of the galactic DM haloes, as predicted by the
hierarchical clustering scenario, but it does not contain morphological
classification nor chemical evolution. We find that at z< 1.5 both models are
consistent with the available data on the LD of galaxies in all the considered
bands. At high z, the LDs predicted in the PLE model show a peak due to the
formation of ellipticals, whereas the SAM predicts a gradual decrease of the
star formation and of the LD for z> 2.5. At such redshifts the PLE predictions
tend to overestimate the present data in the B band whereas the SAM tends to
underestimate the observed UV LD. As for the stellar MD, the PLE picture
predicts that nearly 50% and 85% of the present stellar mass are in place at
z=4 and z=1, respectively. According to the SAM, 50% and 60% of the present
stellar mass are in place at z=1.2 and z=1, respectively. Both predictions fit
the observed MD up to z=1. At z>1, the PLE model and the SAM tend to
overestimate and underestimate the observed values, respectively. We discuss
the origin of the above model results, and the role of observational
uncertainties (such as dust extinction) in comparing models with observations.Comment: 14 pages, accepted for publication in MNRA
Automated Morphological Classification of SDSS Red Sequence Galaxies
(abridged) In the last decade, the advent of enormous galaxy surveys has
motivated the development of automated morphological classification schemes to
deal with large data volumes. Existing automated schemes can successfully
distinguish between early and late type galaxies and identify merger
candidates, but are inadequate for studying detailed morphologies of red
sequence galaxies. To fill this need, we present a new automated classification
scheme that focuses on making finer distinctions between early types roughly
corresponding to Hubble types E, S0, and Sa. We visually classify a sample of
984 non-starforming SDSS galaxies with apparent sizes >14". We then develop an
automated method to closely reproduce the visual classifications, which both
provides a check on the visual results and makes it possible to extend
morphological analysis to much larger samples. We visually classify the
galaxies into three bulge classes (BC) by the shape of the light profile in the
outer regions: discs have sharp edges and bulges do not, while some galaxies
are intermediate. We separately identify galaxies with features: spiral arms,
bars, clumps, rings, and dust. We find general agreement between BC and the
bulge fraction B/T measured by the galaxy modeling package GIM2D, but many
visual discs have B/T>0.5. Three additional automated parameters -- smoothness,
axis ratio, and concentration -- can identify many of these high-B/T discs to
yield automated classifications that agree ~70% with the visual classifications
(>90% within one BC). Both methods are used to study the bulge vs. disc
frequency as a function of four measures of galaxy 'size': luminosity, stellar
mass, velocity dispersion, and radius. All size indicators show a fall in disc
fraction and a rise in bulge fraction among larger galaxies.Comment: 24 pages, 20 figures, MNRAS accepte
Caecal metastasis from breast cancer presenting as intestinal obstruction
<p>Abstract</p> <p>Background</p> <p>Gastrointestinal metastsasis from the breast cancer are rare. We report a patient who presented with intestinal obstruction due to solitary caecal metastasis from infiltrating ductal carcinoma of breast. We also review the available literature briefly.</p> <p>Case presentation</p> <p>A 72 year old lady with past history of breast cancer presented with intestinal obstruction due to a caecal mass. She underwent an emergency right hemicolectomy. The histological examination of the right hemicolectomy specimen revealed an adenocarcinoma in caecum staining positive for Cytokeratin 7 and Carcinoembryonic antigen and negative for Cytokeratin 20, CDX2 and Estrogen receptor. Eight out of 11 mesenteric nodes showed tumour deposits. A histological diagnosis of metastatic breast carcinoma was given.</p> <p>Conclusion</p> <p>To the best of our knowledge, this is the first case report of solitary metastasis to caecum from infiltrating ductal carcinoma of breast. Awareness of this possibility will aid in appropriate management of such patients.</p
On the buildup of massive early-type galaxies at z<~1. I- Reconciling their hierarchical assembly with mass-downsizing
Several studies have tried to ascertain whether or not the increase in
abundance of the early-type galaxies (E-S0a's) with time is mainly due to major
mergers, reaching opposite conclusions. We have tested it directly through
semi-analytical modelling, by studying how the massive early-type galaxies with
log(M_*/Msun)>11 at z~0 (mETGs) would have evolved backwards-in-time, under the
hypothesis that each major merger gives place to an early-type galaxy. The
study was carried out just considering the major mergers strictly reported by
observations at each redshift, and assuming that gas-rich major mergers
experience transitory phases of dust-reddened, star-forming galaxies (DSFs).
The model is able to reproduce the observed evolution of the galaxy LFs at
z<~1, simultaneously for different rest-frame bands (B, I, and K) and for
different selection criteria on color and morphology. It also provides a
framework in which apparently-contradictory results on the recent evolution of
the luminosity function (LF) of massive, red galaxies can be reconciled, just
considering that observational samples of red galaxies can be significantly
contaminated by DSFs. The model proves that it is feasible to build up ~50-60%
of the present-day mETG population at z<~1 and to reproduce the observational
excess by a factor of ~4-5 of late-type galaxies at 0.8<z<1 through the
coordinated action of wet, mixed, and dry major mergers, fulfilling global
trends that are in general agreement with mass-downsizing. The bulk of this
assembly takes place during ~1 Gyr elapsed at 0.8<z<1. The model suggests that
major mergers have been the main driver for the observational migration of mass
from the massive-end of the blue galaxy cloud to that of the red sequence in
the last ~8 Gyr.(Abridged)Comment: Accepted for publication in Astronomy & Astrophysics; 21 pages, 8
figures. Minor corrections included, shortened title. Results and conclusions
unchange
The properties of field elliptical galaxies at intermediate redshift. III: the Fundamental Plane and the evolution of stellar populations from z~0.4 to z=0
We report on the study of a sample of 25 field early-type galaxies, in the
redshift range z~0.1-0.5, selected on the basis of colours and morphology from
the HST-MDS. Field early-type galaxies define a tight Fundamental Plane (FP)
out to z~0.4, with scatter unchanged with respect to local samples, within the
observational errors. The intermediate redshift FP is offset with respect to
the FP of the Coma Cluster. The offset of the FP is found to increase with
redshift. The evolution of the FP is studied quantitatively with a
Bayesian-Montecarlo technique. By applying this technique, we find that the
offset of the intercept of the FP (\Delta \gamma) with respect to the local FP
increases as \Delta \gamma = \tau z with the following 68 per cent limits:
0.33<\tau<0.44 (for \Omega=1, \Omega_{\Lambda}=0) or 0.44<\tau<0.56 (for
\Omega=0.3,\Omega_{\Lambda}=0.7). In addition, we interpret the results in
terms of the evolution of the stellar populations, under the assumption of
passive evolution. In a single-burst scenario, the observed properties are
consistent with those of a stellar population formed at z>2 (for \Omega=1,
\Omega_{\Lambda}=0, H_0=50 \kms Mpc^{-1}) or 0.8<z<1.6 (for \Omega=0.3,
\Omega_{\Lambda}=0.7, H_0=65 \kms Mpc^{-1}). If a small fraction of the stellar
mass is formed in a secondary burst, the primary burst may have occurred at
higher z. Finally, the intercept and scatter of the FP found for field
early-type galaxies and for cluster data at z~0.4 are mutually consistent,
within the observational errors. If higher redshift (up to z=0.83) cluster data
are considered, the ages of the stellar populations of field early-type
galaxies inferred from a single-burst scenario are found to be marginally
smaller than the ages derived for the cluster galaxies. [shortened]Comment: 19 pages, 23 figures, MNRAS, accepte
Genetic Determinants of Lipid Traits in Diverse Populations from the Population Architecture using Genomics and Epidemiology (PAGE) Study
For the past five years, genome-wide association studies (GWAS) have identified hundreds of common variants associated with human diseases and traits, including high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglyceride (TG) levels. Approximately 95 loci associated with lipid levels have been identified primarily among populations of European ancestry. The Population Architecture using Genomics and Epidemiology (PAGE) study was established in 2008 to characterize GWAS–identified variants in diverse population-based studies. We genotyped 49 GWAS–identified SNPs associated with one or more lipid traits in at least two PAGE studies and across six racial/ethnic groups. We performed a meta-analysis testing for SNP associations with fasting HDL-C, LDL-C, and ln(TG) levels in self-identified European American (∼20,000), African American (∼9,000), American Indian (∼6,000), Mexican American/Hispanic (∼2,500), Japanese/East Asian (∼690), and Pacific Islander/Native Hawaiian (∼175) adults, regardless of lipid-lowering medication use. We replicated 55 of 60 (92%) SNP associations tested in European Americans at p<0.05. Despite sufficient power, we were unable to replicate ABCA1 rs4149268 and rs1883025, CETP rs1864163, and TTC39B rs471364 previously associated with HDL-C and MAFB rs6102059 previously associated with LDL-C. Based on significance (p<0.05) and consistent direction of effect, a majority of replicated genotype-phentoype associations for HDL-C, LDL-C, and ln(TG) in European Americans generalized to African Americans (48%, 61%, and 57%), American Indians (45%, 64%, and 77%), and Mexican Americans/Hispanics (57%, 56%, and 86%). Overall, 16 associations generalized across all three populations. For the associations that did not generalize, differences in effect sizes, allele frequencies, and linkage disequilibrium offer clues to the next generation of association studies for these traits
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