61 research outputs found
Insights into the reionization epoch from cosmic-noon-CIV emitters in the VANDELS survey
Recently, intense emission from nebular C III] and C IV emission lines have
been observed in galaxies in the epoch of reionization () and have been
proposed as the prime way of measuring their redshift and studying their
stellar populations. These galaxies might represent the best examples of cosmic
reionizers, as suggested by recent low-z observations of Lyman Continuum
emitting galaxies, but it is hard to directly study the production and escape
of ionizing photons at such high redshifts. The ESO spectroscopic public survey
VANDELS offers the unique opportunity to find rare examples of such galaxies at
cosmic noon (), thanks to the ultra deep observations available. We
have selected a sample of 39 galaxies showing C IV emission, whose origin
(after a careful comparison to photoionization models) can be ascribed to star
formation and not to AGN. By using a multi-wavelength approach, we determine
their physical properties including metallicity and ionization parameter and
compare them to the properties of the parent population to understand what are
the ingredients that could characterize the analogs of the cosmic reionizers.
We find that C IV emitters are galaxies with high photons production efficiency
and there are strong indications that they might have also large escape
fraction: given the visibility of C IV in the epoch of reionization this could
become the best tool to pinpoint the cosmic reioinzers.Comment: 15 pages, 10 figures, resubmitted to A&A after addressing the referee
comment
The ionizing photon production efficiency of bright z2-5 galaxies
We investigate the production efficiency of ionizing photons ()
of 1174 galaxies with secure redshift at z=2-5 from the VANDELS survey to
determine the relation between ionizing emission and physical properties of
bright and massive sources. We constrain and galaxy physical
parameters by means of spectro-photometric fits performed with the BEAGLE code.
The analysis exploits the multi-band photometry in the VANDELS fields, and the
measurement of UV rest-frame emission lines (CIII], HeII, OIII]) from deep VIMOS spectra. We find no clear evolution
of with redshift within the probed range. The ionizing efficiency
slightly increases at fainter , and bluer UV slopes, but these trends
are less evident when restricting the analysis to a complete subsample at
log(M/M)9.5. We find a significant trend of increasing
with increasing EW(Ly), with an average
log(/Hz erg)25 at EW50\AA, and a higher ionizing
efficiency for high-EW CIII] and OIII] emitters.
The most significant correlations are found with respect to stellar mass,
specific star-formation rate (sSFR) and SFR surface density ().
The relation between and sSFR shows a monotonic increase from
log(/Hz erg) 24.5 at log(sSFR)-9.5 to
25.5 at log(sSFR)-7.5, a low scatter and little dependence
on mass. The objects above the main-sequence of star-formation consistently
have higher-than-average . A clear increase of with
is also found, with log(/Hz erg)25 for
objects at 10 M.(Abridged)Comment: 11 pages, 9 figures, accepted for publication in A&
Early Results from GLASS-JWST. XIX: A High Density of Bright Galaxies at in the Abell 2744 Region
We report the detection of a high density of redshift galaxies
behind the foreground cluster Abell 2744, selected from imaging data obtained
recently with NIRCam onboard {\it JWST} by three programs -- GLASS-JWST,
UNCOVER, and DDT\#2756. To ensure robust estimates of the lensing magnification
, we use an improved version of our model that exploits the first epoch of
NIRCam images and newly obtained MUSE spectra, and avoids regions with
where the uncertainty may be higher. We detect seven bright
galaxies with demagnified rest-frame mag,
over an area of sq. arcmin. Taking into account photometric
incompleteness and the effects of lensing on luminosity and cosmological
volume, we find that the density of galaxies in the field is
about () larger than the average at mag reported so far. The density is even higher when considering only
the GLASS-JWST data, which are the deepest and the least affected by
magnification and incompleteness. The GLASS-JWST field contains 5 out of 7
galaxies, distributed along an apparent filamentary structure of 2 Mpc in
projected length, and includes a close pair of candidates with mag having a projected separation of only 16 kpc. These findings suggest
the presence of a overdensity in the field. In addition to
providing excellent targets for efficient spectroscopic follow-up observations,
our study confirms the high density of bright galaxies observed in early {\it
JWST} observations, but calls for multiple surveys along independent lines of
sight to achieve an unbiased estimate of their average density and a first
estimate of their clustering.Comment: Accepted for publication in ApJL, 13 pages, 4 figure
Non-AIDS defining cancers in the D:A:D Study-time trends and predictors of survival : a cohort study
BACKGROUND:Non-AIDS defining cancers (NADC) are an important cause of morbidity and mortality in HIV-positive individuals. Using data from a large international cohort of HIV-positive individuals, we described the incidence of NADC from 2004-2010, and described subsequent mortality and predictors of these.METHODS:Individuals were followed from 1st January 2004/enrolment in study, until the earliest of a new NADC, 1st February 2010, death or six months after the patient's last visit. Incidence rates were estimated for each year of follow-up, overall and stratified by gender, age and mode of HIV acquisition. Cumulative risk of mortality following NADC diagnosis was summarised using Kaplan-Meier methods, with follow-up for these analyses from the date of NADC diagnosis until the patient's death, 1st February 2010 or 6 months after the patient's last visit. Factors associated with mortality following NADC diagnosis were identified using multivariable Cox proportional hazards regression.RESULTS:Over 176,775 person-years (PY), 880 (2.1%) patients developed a new NADC (incidence: 4.98/1000PY [95% confidence interval 4.65, 5.31]). Over a third of these patients (327, 37.2%) had died by 1st February 2010. Time trends for lung cancer, anal cancer and Hodgkin's lymphoma were broadly consistent. Kaplan-Meier cumulative mortality estimates at 1, 3 and 5 years after NADC diagnosis were 28.2% [95% CI 25.1-31.2], 42.0% [38.2-45.8] and 47.3% [42.4-52.2], respectively. Significant predictors of poorer survival after diagnosis of NADC were lung cancer (compared to other cancer types), male gender, non-white ethnicity, and smoking status. Later year of diagnosis and higher CD4 count at NADC diagnosis were associated with improved survival. The incidence of NADC remained stable over the period 2004-2010 in this large observational cohort.CONCLUSIONS:The prognosis after diagnosis of NADC, in particular lung cancer and disseminated cancer, is poor but has improved somewhat over time. Modifiable risk factors, such as smoking and low CD4 counts, were associated with mortality following a diagnosis of NADC
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