72 research outputs found
The extragalactic background and its fluctuations in the far-infrared wavelengths
A Cosmic Far-InfraRed Background (CFIRB) has long been predicted that would
traces the intial phases of galaxy formation. It has been first detected by
Puget et al.(1996) using COBE data and has been later confirmed by several
recent studies (Fixsen et al. 1998, Hauser et al. 1998, Lagache et al. 1999).
We will present a new determination of the CFIRB that uses for the first time,
in addition to COBE data, two independent gas tracers: the HI survey of
Leiden/Dwingeloo (hartmann, 1998) and the WHAM H survey (Reynolds et
al 1998). We will see that the CFIRB above 100 micron is now very well
constrained. The next step is to see if we can detect its fluctuations. To
search for the CFIRB fluctuations, we have used the FIRBACK observations.
FIRBACK is a deep cosmological survey conducted at 170 micron with ISOPHOT
(Dole et al., 2000). We show that the emission of unresolved extra-galactic
sources clearly dominates, at arcminute scales, the background fluctuations in
the lowest galactic emission regions. This is the first detection of the CFIRB
fluctuations.Comment: To appear in "ISO Surveys of a Dusty Universe", Workshop at Ringberg
Castle, November 8 - 12, 199
FIRBACK Source Counts and Cosmological Implications
FIRBACK is a one of the deepest surveys performed at 170 microns with ISOPHOT
onboard ISO, and is aimed at the study of cosmic far infrared background
sources. About 300 galaxies are detected in an area of four square degrees, and
source counts present a strong slope of 2.2 on an integral "logN-logS" plot,
which cannot be due to cosmological evolution if no K-correction is present.
The resolved sources account for less than 10% of the Cosmic Infrared
Background at 170 microns. In order to understand the nature of the sources
contributing to the CIB, and to explain deep source counts at other
wavelengths, we have developed a phenomenological model, which constrains in a
simple way the luminosity function evolution with redshift, and fits all the
existing deep source counts from the mid-infrared to the submillimetre range.
Images, materials and papers available on the FIRBACK web:
http://wwwfirback.ias.u-psud.fr wwwfirback.ias.u-psud.frComment: proceedings of "ISO Surveys of a Dusty Universe", eds. D. Lemke, M.
Stickel, K. Wilke, Ringberg, 8-12 Nov 1999, to appear in Springer 'Lecture
Notes of Physics'. 8 pages, 7 eps figures, .sty include
The Cosmic Far-Infrared Background Buildup Since Redshift 2 at 70 and 160 microns in the COSMOS and GOODS fields
The Cosmic Far-Infrared Background (CIB) at wavelengths around 160 {\mu}m
corresponds to the peak intensity of the whole Extragalactic Background Light,
which is being measured with increasing accuracy. However, the build up of the
CIB emission as a function of redshift, is still not well known. Our goal is to
measure the CIB history at 70 {\mu}m and 160 {\mu}m at different redshifts, and
provide constraints for infrared galaxy evolution models. We use complete deep
Spitzer 24 {\mu}m catalogs down to about 80 {\mu}Jy, with spectroscopic and
photometric redshifts identifications, from the GOODS and COSMOS deep infrared
surveys covering 2 square degrees total. After cleaning the Spitzer/MIPS 70
{\mu}m and 160 {\mu}m maps from detected sources, we stacked the far-IR images
at the positions of the 24 {\mu}m sources in different redshift bins. We
measured the contribution of each stacked source to the total 70 and 160 {\mu}m
light, and compare with model predictions and recent far-IR measurements made
with Herschel/PACS on smaller fields. We have detected components of the 70 and
160 {\mu}m backgrounds in different redshift bins up to z ~ 2. The contribution
to the CIB is maximum at 0.3 <= z <= 0.9 at 160{\mu}m (and z <= 0.5 at 70
{\mu}m). A total of 81% (74%) of the 70 (160) {\mu}m background was emitted at
z < 1. We estimate that the AGN relative contribution to the far-IR CIB is less
than about 10% at z < 1.5. We provide a comprehensive view of the CIB buildup
at 24, 70, 100, 160 {\mu}m. IR galaxy models predicting a major contribution to
the CIB at z < 1 are in agreement with our measurements, while our results
discard other models that predict a peak of the background at higher redshifts.
Our results are available online http://www.ias.u-psud.fr/irgalaxies/ .Comment: Accepted in Astronomy & Astrophysic
FIRBACK Source Counts and Cosmological Implications
FIRBACK is a one of the deepest surveys performed at 170 microns with ISOPHOT
onboard ISO, and is aimed at the study of cosmic far infrared background
sources. About 300 galaxies are detected in an area of four square degrees, and
source counts present a strong slope of 2.2 on an integral "logN-logS" plot,
which cannot be due to cosmological evolution if no K-correction is present.
The resolved sources account for less than 10% of the Cosmic Infrared
Background at 170 microns. In order to understand the nature of the sources
contributing to the CIB, and to explain deep source counts at other
wavelengths, we have developed a phenomenological model, which constrains in a
simple way the luminosity function evolution with redshift, and fits all the
existing deep source counts from the mid-infrared to the submillimetre range.
Images, materials and papers available on the FIRBACK web:
http://wwwfirback.ias.u-psud.fr wwwfirback.ias.u-psud.frComment: proceedings of "ISO Surveys of a Dusty Universe", eds. D. Lemke, M.
Stickel, K. Wilke, Ringberg, 8-12 Nov 1999, to appear in Springer 'Lecture
Notes of Physics'. 8 pages, 7 eps figures, .sty include
Specific star-formation and the relation to stellar mass from 0<z<2 as seen in the far-infrared at 70 and 160mu
We use the Spitzer Wide-area InfraRed Extragalactic Legacy Survey (SWIRE) to
explore the specific star-formation activity of galaxies and their evolution
near the peak of the cosmic far-infrared (FIR) background at 70 and 160um. We
use a stacking analysis to determine the mean FIR properties of well defined
subsets of galaxies at flux levels well below the FIR catalogue detection
limits of SWIRE and other Spitzer surveys. We tabulate the contribution of
different subsets of galaxies to the FIR background at 70um and 160um. These
long wavelengths provide a good constraint on the bolometric, obscured
emission. The large area provides good constraints at low z and in finer
redshift bins than previous work. At all redshifts we find that the specific
FIR Luminosity (sLFIR) decreases with increasing mass, following a trend
L_FIR/M* propto M_* ^beta with beta =-0.38\pm0.14. This is a more continuous
change than expected from the {Delucia2007} semi-analytic model suggesting
modifications to the feedback prescriptions. We see an increase in the sLFIR by
about a factor of ~100 from 0<z<2 and find that the sLFIR evolves as
(1+z)^alpha with alpha=4.4\pm0.3 for galaxies with 10.5 < log M*/Msun < 12.
This is considerably steeper than the {Delucia2007} semi-analytic model (alpha
\sim 2.5). When separating galaxies into early and late types on the basis of
the optical/IR spectral energy distributions we find that the decrease in sLFIR
with stellar mass is stronger in early type galaxies (beta ~ -0.46), while late
type galaxies exhibit a flatter trend (beta \sim -0.15). The evolution is
strong for both classes but stronger for the early type galaxies. The early
types show a trend of decreasing strength of evolution as we move from lower to
higher masses while the evolution of the late type galaxies has little
dependence on stellar mass. We suggest that in late-type galaxies we are seeing
a consistently declining sSFR..Comment: v2 Update doesn't change the content of the paper, but now includes
data files for the plots Fig 5-13 (all.plotdat, spi.plotdat and ell.plotdat
on arXiv package
IRAC Imaging of Lockman Hole
IRAC imaging of a 4'7x4'7 area in the Lockman Hole detected over 400 galaxies
in the IRAC 3.6 micron and 4.5 micron bands, 120 in the 5.8 micron, and 80 in
the 8 micron bandin 30 minutes of observing time. Color-color diagrams suggest
that about half of these galaxies are at redshifts 0.6<z<1.3 with about a
quarter at higher redshifts (z>1.3). We also detect IRAC counterparts for 6 of
the 7 SCUBA sources and all 9 XMM sources in this area. The detection of the
counterparts of the SCUBA sources and galaxies at z>1.3 demonstrates the
ability of IRAC to probe the universe at very high redshifts.Comment: 11 pages, 2 figures. accepted by ApJS, Spizter Special Issu
FIRBACK: III. Catalog, Source counts, and cosmological implications of the 170 micron ISO Deep survey
The FIRBACK (Far Infrared BACKground) survey is one of the deepest imaging
surveys carried out at 170 microns with ISOPHOT onboard ISO, and is aimed at
the study of the structure of the Cosmic Far Infrared Background. This paper
provides the analysis of resolved sources. After a validated process of data
reduction and calibration, we perform intensive simulations to optimize the
source extraction, measure the confusion noise (sigma_c = 45 mJy), and give the
photometric and astrometric accuracies. 196 galaxies with flux S > 3 sigma_c
are detected in the area of 3.89 square degrees. Counts of sources with flux S
> 4 sigma_c present a steep slope of 3.3 +/- 0.6 on a differential "logN-logS"
plot between 180 and 500 mJy. As a consequence, the confusion level is high and
will impact dramatically on future IR deep surveys. This strong evolution,
compared with a slope of 2.5 from Euclidian geometry, is in line with models
implying a strongly evolving Luminous Infrared Galaxy population. The resolved
sources account for less than 10% of the Cosmic Infrared Background at 170
microns, which is expected to be resolved into sources in the 1 to 10 mJy
range.Comment: Accepted for publication in A&A. 16 pages, includes new aa.cls.
Tables 7 to 13 included here will appear on the electronic version of A&A and
at the CDS. Paper, catalog and images (with better quality) also available at
http://wwwfirback.ias.u-psud.fr and http://mips.as.arizona.edu/~hdole/firbac
Evolution of the Far-Infrared-Radio Correlation and Infrared SEDs of Massive Galaxies over z = 0 - 2
We investigate the far-infrared-radio correlation (FRC) of
stellar-mass-selected galaxies in the Extended Chandra Deep Field South using
far-infrared imaging from Spitzer and radio imaging from the Very Large Array
and Giant Metre-Wave Radio Telescope. We stack in redshift bins to probe
galaxies below the noise and confusion limits. Radio fluxes are K-corrected
using observed flux ratios, leading to tentative evidence for an evolution in
spectral index. We compare spectral energy distribution (SED) templates of
local galaxies for K-correcting FIR fluxes, and show that the data are best fit
by a quiescent spiral template (M51) rather than a warm starburst (M82) or
ULIRG (Arp220), implying a predominance of cold dust in massive galaxies at
high redshift. In contrast we measure total infrared luminosities that are
consistent with high star-formation rates. We observe that the FRC index (q)
does not evolve significantly over z=0-2 when computed from K-corrected 24 or
160-mum photometry, but that using 70-mum fluxes leads to an apparent decline
in q beyond z~1. This suggests some change in the SED at high redshift, either
a steepening of the spectrum at rest-frame ~25-35mum or a deficiency at ~70mum
leading to a drop in the total infrared/radio ratios. We compare our results to
other work in the literature and find synergies with recent findings on the
high-redshift FRC, high specific star-formation rates of massive galaxies and
the cold dust temperatures in these galaxies.Comment: 21 pages, 13 figures, accepted for publication in MNRA
The joint influence of area income, income inequality, and immigrant density on adverse birth outcomes: a population-based study
<p>Abstract</p> <p>Background</p> <p>The association between area characteristics and birth outcomes is modified by race. Whether such associations vary according to social class indicators beyond race has not been assessed.</p> <p>Methods</p> <p>This study evaluated effect modification by maternal birthplace and education of the relationship between neighbourhood characteristics and birth outcomes of newborns from 1999â2003 in the province of QuĂ©bec, Canada (N = 353,120 births). Areas (N = 143) were defined as administrative local health service delivery districts. Multi-level logistic regression was used to model the association between three area characteristics (median household income, immigrant density and income inequality) and the two outcomes preterm birth (PTB) and small-for-gestational age (SGA) birth. Effect modification by social class indicators was evaluated in analyses stratified according to maternal birthplace and education.</p> <p>Results</p> <p>Relative to the lowest tertile, high median household income was associated with SGA birth among Canadian-born mothers (odds ratio (OR) 1.13, 95% confidence interval (CI) 1.06, 1.20) and mothers with high school education or less (OR 1.13, 95% CI 1.02, 1.24). Associations between median household income and PTB were weaker. Relative to the highest tertile, low immigrant density was associated with a lower odds of PTB among foreign-born mothers (OR 0.79, 95% CI 0.63, 1.00) but a higher odds of PTB among Canadian-born mothers (OR 1.14, 95% CI 1.07, 1.21). Associations with income inequality were weak or absent.</p> <p>Conclusion</p> <p>The association between area factors and birth outcomes is modified by maternal birthplace and education. Studies have found that race interacts in a similar manner. Public health policies focussed on perinatal health must consider the interaction between individual and area characteristics.</p
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