157 research outputs found
Phenotypic characterization of Adig null mice suggests roles for adipogenin in the regulation of fat mass accrual and leptin secretion
Adipogenin (Adig) is an adipocyte-enriched transmembrane protein. Its expression is induced during adipogenesis in rodent cells, and a recent genome-wide association study associated body mass index (BMI)-adjusted leptin levels with the ADIG locus. In order to begin to understand the biological function of Adig, we studied adipogenesis in Adig-deficient cultured adipocytes and phenotyped Adig null (Adigâ/â) mice. Data from Adig-deficient cells suggest that Adig is required for adipogenesis. In vivo, Adigâ/â mice are leaner than wild-type mice when fed a high-fat diet and when crossed with Ob/Ob hyperphagic mice. In addition to the impact on fat mass accrual, Adig deficiency also reduces fat-mass-adjusted plasma leptin levels and impairs leptin secretion from adipose explants, suggesting an additional impact on the regulation of leptin secretion
Limits on the LyC signal from z~3 sources with secure redshift and HST coverage in the E-CDFS field
Aim: We aim to measure the LyC signal from a sample of sources in the Chandra
deep field south. We collect star-forming galaxies (SFGs) and active galactic
nuclei (AGN) with accurate spectroscopic redshifts, for which Hubble Space
Telescope (HST) coverage and multi-wavelength photometry are available. Method:
We selected a sample of about 200 sources at z~3. Taking advantage of HST
resolution, we applied a careful cleaning procedure and rejected sources
showing nearby clumps with different colours, which could be lower-z
interlopers. Our clean sample consisted of 86 SFGs (including 19 narrow-band
selected Lya emitters) and 8 AGN (including 6 detected in X-rays). We measured
the LyC flux from aperture photometry in four narrow-band filters covering
wavelengths below a 912 A rest frame (3.11<z<3.53). We estimated the ratio
between ionizing (LyC flux) and 1400 A non-ionizing emissions for AGN and
galaxies. Results: By running population synthesis models, we assume an average
intrinsic L(1400 A)/L(900 A) ratio of 5 as the representative value for our
sample. With this value and an average treatment of the lines of sight of the
inter-galactic medium, we estimate the LyC escape fraction relative to the
intrinsic value (fesc_rel(LyC)). We do not directly detect ionizing radiation
from any individual SFG, but we are able to set a 1(2)sigma upper limit of
fesc_rel(LyC)<12(24)%. This result is consistent with other non-detections
published in the literature. No meaningful limits can be calculated for the
sub-sample of Lya emitters. We obtain one significant direct detection for an
AGN at z=3.46, with fesc_rel(LyC) = (72+/-18)%. Conclusions: Our upper limit on
fescrel(LyC) implies that the SFGs studied here do not present either the
physical properties or the geometric conditions suitable for efficient
LyC-photon escape.Comment: Accepted for publication in A&A on Jan 5th, 201
Antipodean Theory for Educational Research
published_or_final_versio
The VANDELS survey: A strong correlation between Ly equivalent width and stellar metallicity at
We present the results of a new study investigating the relationship between
observed Ly equivalent width ((Ly)) and the
metallicity of the ionizing stellar population () for a sample of
star-forming galaxies at drawn from the VANDELS survey.
Dividing our sample into quartiles of rest-frame (Ly)
across the range -58 \unicode{xC5} \lesssim (Ly)
\lesssim 110 \unicode{xC5} we determine from full spectral
fitting of composite far-ultraviolet (FUV) spectra and find a clear
anti-correlation between (Ly) and . Our results
indicate that decreases by a factor between the lowest
(Ly) quartile
((Ly)\rangle=-18\unicode{xC5}) and the highest
(Ly) quartile
((Ly)\rangle=24\unicode{xC5}). Similarly,
galaxies typically defined as Lyman Alpha Emitters (LAEs;
(Ly) >20\unicode{xC5}) are, on average, metal poor with
respect to the non-LAE galaxy population ((Ly)
\leq20\unicode{xC5}) with
. Finally, based on the best-fitting stellar models, we
estimate that the increasing strength of the stellar ionizing spectrum towards
lower is responsible for of the observed variation
in (Ly) across our sample, with the remaining contribution
() being due to a decrease in the HI/dust covering fractions in
low galaxies.Comment: 10 pages, 6 figures, MNRAS accepte
Stellar properties of z ~ 1 Lyman-break galaxies from ACS slitless grism spectra
Lyman-break galaxies are now regularly found in the high redshift Universe by
searching for the break in the galaxy spectrum caused by the Lyman-limit
redshifted into the optical or even near-IR. At lower redshift, this break is
covered by the GALEX UV channels and small samples of z ~ 1 LBGs have been
presented in the literature. Here we give results from fitting the spectral
energy distributions of a small sub-set of low redshift LBGs and demonstrate
the advantage of including photometric points derived from HST ACS slitless
grism observations. The results show these galaxies to have very young, star
forming populations, while still being massive and dusty. LBGs at low and high
redshift show remarkable similarities in their properties, indicating that the
LBG selection method picks similar galaxies throughout the Universe.Comment: 7 pages, 3 figures, 2 tables, accepted in A&
The VIMOS Ultra Deep Survey: Ly Emission and Stellar Populations of Star-Forming Galaxies at 2<z<2.5
The aim of this paper is to investigate spectral and photometric properties
of 854 faint (<~25 mag) star-forming galaxies (SFGs) at 2<z<2.5 using
the VIMOS Ultra-Deep Survey (VUDS) spectroscopic data and deep multi-wavelength
photometric data in three extensively studied extragalactic fields (ECDFS,
VVDS, COSMOS). These SFGs were targeted for spectroscopy based on their
photometric redshifts. The VUDS spectra are used to measure the UV spectral
slopes () as well as Ly equivalent widths (EW). On average, the
spectroscopically measured (-1.360.02), is comparable to the
photometrically measured (-1.320.02), and has smaller measurement
uncertainties. The positive correlation of with the Spectral Energy
Distribution (SED)-based measurement of dust extinction, E(B-V),
emphasizes the importance of as an alternative dust indicator at high
redshifts. To make a proper comparison, we divide these SFGs into three
subgroups based on their rest-frame Ly EW: SFGs with no Ly
emission (SFG; EW0\AA), SFGs with Ly emission (SFG; EW0\AA), and Ly emitters (LAEs; EW20\AA). The fraction of
LAEs at these redshifts is 10%, which is consistent with previous
observations. We compared best-fit SED-estimated stellar parameters of the
SFG, SFG and LAE samples. For the luminosities probed here
(L), we find that galaxies with and without Ly in emission
have small but significant differences in their SED-based properties. We find
that LAEs have less dust, and lower star-formation rates (SFR) compared to
non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though
the difference is smaller and less significant compared to the SFR and E(B-V). [abridged]Comment: Accepted for publication in A&A, 19 pages, 10 figures, 1 tabl
The impact of the Star Formation Histories on the SFR-M relation at z2
In this paper we investigate the impact of different star formation histories
(SFHs) on the relation between stellar mass M and star formation rate
(SFR) using a sample of galaxies with reliable spectroscopic redshift zspec>2
drawn from the VIMOS Ultra-Deep Survey (VUDS). We produce an extensive database
of dusty model galaxies, calculated starting from the new library of single
stellar population (SSPs) models presented in Cassara' et al. 2013 and weighted
by a set of 28 different SFHs based on the Schmidt function, and characterized
by different ratios of the gas infall time scale to the star
formation efficiency . The treatment of dust extinction and re-emission
has been carried out by means of the radiative transfer calculation. The
spectral energy distribution (SED) fitting technique is performed by using
GOSSIP+, a tool able to combine both photometric and spectroscopic information
to extract the best value of the physical quantities of interest, and to
consider the Intergalactic Medium (IGM) attenuation as a free parameter. We
find that the main contribution to the scatter observed in the
plane is the possibility of choosing between different families of SFHs in the
SED fitting procedure, while the redshift range plays a minor role. The
majority of the galaxies, at all cosmic times, are best-fit by models with SFHs
characterized by a high ratio. We discuss the
reliability of the presence of a small percentage of dusty and highly star
forming galaxies, in the light of their detection in the FIR.Comment: 14 pages, 13 figures, accepted for pubblication in A&
The VIMOS Ultra Deep Survey First Data Release: spectra and spectroscopic redshifts of 698 objects up to z~6 in CANDELS
This paper describes the first data release (DR1) of the VIMOS Ultra Deep
Survey (VUDS). The DR1 includes all low-resolution spectroscopic data obtained
in 276.9 arcmin2 of the CANDELS-COSMOS and CANDELS-ECFDS survey areas,
including accurate spectroscopic redshifts z_spec and individual spectra
obtained with VIMOS on the ESO-VLT. A total of 698 objects have a measured
redshift, with 677 galaxies, two type-I AGN and a small number of 19
contaminating stars. The targets of the spectroscopic survey are selected
primarily on the basis of their photometric redshifts to ensure a broad
population coverage. About 500 galaxies have z_spec>2, 48 with z_spec>4, and
the highest reliable redshifts reach beyond z_spec=6. This dataset
approximately doubles the number of galaxies with spectroscopic redshifts at
z>3 in these fields. We discuss the general properties of the sample in terms
of the spectroscopic redshift distribution, the distribution of Lyman-alpha
equivalent widths, and physical properties including stellar masses M_star and
star formation rates (SFR) derived from spectral energy distribution fitting
with the knowledge of z_spec. We highlight the properties of the most massive
star-forming galaxies, noting the large range in spectral properties, with
Lyman-alpha in emission or in absorption, and in imaging properties with
compact, multi-component or pair morphologies. We present the catalogue
database and data products. All data are publicly available and can be
retrieved from a dedicated query-based database available at
http://cesam.lam.fr/vuds.Comment: 11 pages, 6 figures, submitted to A&
The Lyman Continuum escape fraction of galaxies at z=3.3 in the VUDS-LBC/COSMOS field
The Lyman continuum (LyC) flux escaping from high-z galaxies into the IGM is
a fundamental quantity to understand the physical processes involved in the
reionization epoch. We have investigated a sample of star-forming galaxies at
z~3.3 in order to search for possible detections of LyC photons escaping from
galaxy halos. UV deep imaging in the COSMOS field obtained with the prime focus
camera LBC at the LBT telescope was used together with a catalog of
spectroscopic redshifts obtained by the VIMOS Ultra Deep Survey (VUDS) to build
a sample of 45 galaxies at z~3.3 with L>0.5L*. We obtained deep LBC images of
galaxies with spectroscopic redshifts in the interval 3.27<z<3.40 both in the R
and deep U bands. A sub-sample of 10 galaxies apparently shows escape
fractions>28% but a detailed analysis of their properties reveals that, with
the exception of two marginal detections (S/N~2) in the U band, all the other 8
galaxies are most likely contaminated by the UV flux of low-z interlopers
located close to the high-z targets. The average escape fraction derived from
the stacking of the cleaned sample was constrained to fesc_rel<2%. The implied
HI photo-ionization rate is a factor two lower than that needed to keep the IGM
ionized at z~3, as observed in the Lyman forest of high-z QSO spectra or by the
proximity effect. These results support a scenario where high redshift,
relatively bright (L>0.5L*) star-forming galaxies alone are unable to sustain
the level of ionization observed in the cosmic IGM at z~3. Star-forming
galaxies at higher redshift and at fainter luminosities (L<<L*) can be the
major contributors to the reionization of the Universe only if their physical
properties are subject to rapid changes from z~3 to z~6-10. Alternatively,
ionizing sources could be discovered looking for fainter sources among the AGN
population at high-z.Comment: 21 pages, 9 figures. Accepted for publication in A&
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