12 research outputs found
The Galaxy Structure-Redshift Relationship
There exists a gradual, but persistent, evolutionary effect in the galaxy
population such that galaxy structure and morphology change with redshift. This
galaxy structure-redshift relationship is such that an increasingly large
fraction of all bright and massive galaxies at redshifts 2 < z < 3 are
morphologically peculiar at wavelengths from rest-frame ultraviolet to
rest-frame optical. There are however examples of morphologically selected
spirals and ellipticals at all redshifts up to z ~ 3. At lower redshift, the
bright galaxy population smoothly transforms into normal ellipticals and
spirals. The rate of this transformation strongly depends on redshift, with the
swiftest evolution occurring between 1 < z < 2. This review characterizes the
galaxy structure-redshift relationship, discusses its various physical causes,
and how these are revealing the mechanisms responsible for galaxy formation.Comment: 20 pages, 8 figures. Invited Review to appear in "Penetrating Bars
Through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes A New Note", ed.
D. Block et a
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
Galaxy luminosity function per morphological type up to z=1.2
We have computed the evolution of the rest-frame B-band luminosity function
(LF) for bulge and disk-dominated galaxies since z=1.2. We use a sample of 605
spectroscopic redshifts with I_{AB}<24 in the Chandra Deep Field South from the
VIMOS-VLT Deep Survey, 3555 galaxies with photometric redshifts from the
COMBO-17 multi-color data, coupled with multi-color HST/ACS images from the
Great Observatories Origin Deep Survey. We split the sample in bulge- and
disk-dominated populations on the basis of asymmetry and concentration
parameters measured in the rest-frame B-band. We find that at z=0.4-0.8, the LF
slope is significantly steeper for the disk-dominated population (\alpha=-1.19
\pm 0.07) compared to the bulge-dominated population (\alpha=-0.53 \pm 0.13).
The LF of the bulge-dominated population is composed of two distinct
populations separated in rest-frame color: 68% of red (B-I)_{AB}>0.9 and bright
galaxies showing a strongly decreasing LF slope \alpha=+0.55 \pm 0.21, and 32%
of blue (B-I)_{AB}<0.9 and more compact galaxies which populate the LF
faint-end. We observe that red bulge-dominated galaxies are already well in
place at z~1, but the volume density of this population is increasing by a
factor 2.7 between z~1 and z~0.6. It may be related to the building-up of
massive elliptical galaxies in the hierarchical scenario. In addition, we
observe that the blue bulge-dominated population is dimming by 0.7 magnitude
between z~1 and z~0.6. Galaxies in this faint and more compact population could
possibly be the progenitors of the local dwarf spheroidal galaxies.Comment: 9 pages, 4 figures, 2 tables, accepted for publication in Astronomy
and Astrophysic
The host galaxy of GRB 011121: Morphology and Spectral Energy Distribution
(Abridged) We present a detailed study of the host galaxy of GRB 011121 (at z
= 0.36) based on high-resolution imaging in 5 broad-band, optical and
near-infrared filters with HST and VLT/ISAAC. The surface brightness profile of
this galaxy is best fitted by a Sersic law with index ~ 2 - 2.5 and a rather
large effective radius (~ 7.5 kpc). Both the morphological analysis and the
F450W - F702W colour image suggest that the host galaxy of GRB 011121 is either
a disk-system with a rather small bulge, or one hosting a central,
dust-enshrouded starburst. Hence, we modeled the integrated spectral energy
distribution of this galaxy by combining stellar population and radiative
transfer models, assuming properties representative of nearby starburst or
normal star-forming, Sbc-like galaxies. A range of plausible fitting solutions
indicates that the host galaxy of GRB 011121 has a stellar mass of 3.1 - 6.9
x10^9 Msun, stellar populations with a maximum age ranging from 0.4 to 2 Gyr,
and a metallicity ranging from 1 to 29 per cent of the solar value. Starburst
models suggest this galaxy to be nearly as opaque as local starbursts (with an
A_V = 0.27 - 0.76 mag). Alternatively, normal star-forming Sbc-like models
suggest a high central opacity whereas A_V = 0.12$ -- 0.57 mag along the line
of sight. For this subluminous galaxy (with L_B/Lstar_B = 0.26), we determine a
model-dependent SFR of 2.4 - 9.4 Msun/yr. The SFR per unit luminosity (9.2 -
36.1 Msun/yr/(L_B/Lstar_B)) is high compared to those of most GRB host
galaxies, but consistent with those of most of the hosts at similar low
redshift. Our results suggest that the host galaxy of GRB 011121 is a rather
large disk-system in a relatively early phase of its star formation history.Comment: accepted for publication in A&
Ultra-deep Spitzer Mid-Infrared Spectroscopy of LIRGs and ULIRGs at z ~ 1-2
We present ultra-deep mid-IR spectra of 48 infrared-luminous galaxies in the
GOODS-South field obtained with the InfraRed Spectrograph (IRS) on the Spitzer
Space Telescope. These galaxies are selected among faint infrared sources (0.14
- 0.5 mJy at 24 um) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the
major contributors to the cosmic infrared background at the most active epochs.
We estimate redshifts for 92% of the sample using PAH and Si absorption
features. Only few of these galaxies (5% at z~1 and 12% at z~2) have their
total infrared luminosity dominated by emission from AGN. The averaged mid-IR
spectra of the z~1 LIRGs and of the z~2 ULIRGs are very similar to the averaged
spectrum of local starbursts and HII-like ULIRGs, respectively. We find that
6.2um PAH equivalent widths reach a plateau of ~1 um for L(24 mu) < 1E11
L(sun). At higher luminosities, EW (6.2 mu) anti-correlates with L(24 um).
Intriguingly, high-z ULIRGs and SMG lie above the local EW (6.2 um) - L(24 um)
relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN
contributions to their dust emission lower than those of local counterparts. A
quantitative analysis of their morphology shows that most of the luminous IR
galaxies have morphologies similar to those of IR-quiet galaxies at the same
redshift. All z~2 ULIRGs of our sample are IR-excess BzK galaxies and most of
them have L(FIR)/L(1600A) ratios higher than those of starburst galaxies at a
given UV slope. The ``IR excess'' (Daddi et al. 2007) is mostly due to strong
7.7 um PAH emission and under-estimation of UV dust extinction. On the basis of
the AGN-powered L (6 um) continuum measured directly from the mid-IR spectra,
we estimate an average intrinsic X-ray AGN luminosity of L(2-10 keV) = (0.1 +/-
0.6) 1E43 erg/s, a value substantially lower than the prediction by Daddi et
al. (2007).Comment: 45 pages, 36 figures, 2 tables, accepted for publication on Ap
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Comparing dynamical and photometric-stellar masses of early-type galaxies at z ~ 1
The purpose of this study is to explore the relationship between galaxy
stellar masses, based on multiwavelength photometry spectral template fitting
and dynamical masses based on published velocity dispersion measurements, for a
sample of 48 early-type galaxies at z ~ 1 with HST/ACS morphological
information. We determine photometric-stellar masses and perform a quantitative
morphological analysis of cluster and field galaxies at redshift 0.6 < z < 1.2,
using ground- and space-based multiwavelegth data available on the GOODS-S
field and on the field around the X-ray luminous cluster RDCS1252.9-2927 at z =
1.24. We use multi-band photometry over 0.4-8um from HST/ACS, VLT/ISAAC and
Spitzer/IRAC to estimate photometric-stellar masses using Composite Stellar
Population (CSP) templates computed with PEGASE.2 models. We compare stellar
masses with those obtained using CSPs built with Bruzual & Charlot and Maraston
models. We then compare photometric-stellar mass and dynamical mass estimates
as a function of morphological parameters obtained from HST/ACS imaging. Based
on our sample, which spans the mass range log(Mphot)=[10, 11.5], we find that
1) PEGASE.2, BC03, M05 yield consistent photometric-stellar masses for
early-type galaxies at z ~ 1 with a small scatter (0.15 dex rms); 2) adopting a
Kroupa IMF, photometric-stellar masses match dynamical mass estimates for
early-type galaxies with an average offset of 0.27 dex; 3) assuming a costant
IMF, increasing dark matter fraction with the increasing galaxy mass can
explain the observed trend.Comment: 12 pages, 10 figures, 1 table, accepted for publication in Astronomy
and Astrophysic
Plasma lysosphingolipids in GRN-related diseases: Monitoring lysosomal dysfunction to track disease progression
International audienceGRN mutations are among the main genetic causes of frontotemporal dementia (FTD). Considering the progranulin involvement in lysosomal homeostasis, we aimed to evaluate if plasma lysosphingolipids (lysoSPL) are increased in GRN mutation carriers, and whether they might represent relevant fluid-based biomarkers in GRN-related diseases. We analyzed four lysoSPL levels in plasmas of 131 GRN carriers and 142 non-carriers, including healthy controls and patients with frontotemporal dementias (FTD) carrying a C9orf72 expansion or without any mutation. GRN carriers consisted of 102 heterozygous FTD patients (FTD-GRN), three homozygous patients with neuronal ceroid lipofuscinosis-11 (CLN-11) and 26 presymptomatic carriers (PS-GRN), the latter with longitudinal assessments. Glucosylsphingosin d18:1 (LGL1), lysosphingomyelins d18:1 and isoform 509 (LSM18:1, LSM509) and lysoglobotriaosylceramide (LGB3) were measured by electrospray ionization-tandem mass spectrometry coupled to ultraperformance liquid chromatography. Levels of LGL1, LSM18:1 and LSM509 were increased in GRN carriers compared to non-carriers (p < 0.0001). No lysoSPL increases were detected in FTD patients without GRN mutations. LGL1 and LSM18:1 progressively increased with age at sampling, and LGL1 with disease duration, in FTD-GRN. Among PS-GRN carriers, LSM18:1 and LGL1 significantly increased over 3.4-year follow-up. LGL1 levels were associated with increasing neurofilaments in presymptomatic carriers. This study evidences an age-dependent increase of β-glucocerebrosidase and acid sphingomyelinase substrates in GRN patients, with progressive changes as early as the presymptomatic phase. Among FTD patients, plasma lysoSPL appear to be uniquely elevated in GRN carriers, and thus might serve as suitable non-invasive disease-tracking biomarkers of progression, specific to the pathophysiological process. Finally, this study might add lysoSPL to the portfolio of fluid-based biomarkers, and pave the way to disease-modifying approaches based on lysosomal function rescue in GRN diseases