Correlated Anisotropies in the Cosmic Far-Infrared Background Detected by MIPS/Spitzer: Constraint on the Bias

We report the detection of correlated anisotropies in the Cosmic Far-Infrared Background at 160 microns. We measure the power spectrum in the Spitzer/SWIRE Lockman Hole field. It reveals unambiguously a strong excess above cirrus and Poisson contributions, at spatial scales between 5 and 30 arcminutes, interpreted as the signature of infrared galaxy clustering. Using our model of infrared galaxy evolution we derive a linear bias b=1.74 \pm 0.16. It is a factor 2 higher than the bias measured for the local IRAS galaxies. Our model indicates that galaxies dominating the 160 microns correlated anisotropies are at z~1. This implies that infrared galaxies at high redshifts are biased tracers of mass, unlike in the local Universe.Comment: ApJ Letters, in pres

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

HerMES: dust attenuation and star formation activity in ultraviolet-selected samples from z 4 to 1.5

We study the link between observed ultraviolet (UV) luminosity, stellar mass and dust attenuation within rest-frame UV-selected samples at z ∼ 4, ∼ 3 and ∼1.5. We measure by stacking at 250, 350 and 500μm in the Herschel/Spectral and Photometric Imaging Receiver images from the Herschel Multi-Tiered Extragalactic Survey (HerMES) program the average infrared luminosity as a function of stellar mass and UV luminosity. We find that dust attenuation is mostly correlated with stellar mass. There is also a secondary dependence with UV luminosity: at a given UV luminosity, dust attenuation increases with stellar mass, while at a given stellar mass it decreases with UV luminosity. We provide new empirical recipes to correct for dust attenuation given the observed UV luminosity and the stellar mass. Our results also enable us to put new constraints on the average relation between star formation rate (SFR) and stellar mass at z ∼ 4, ∼3 and ∼1.5. The SFR–stellar mass relations are well described by power laws (SFR ∝ M 0.7∗), with the amplitudes being similar at z ∼ 4 and ∼3, and decreasing by a factor of 4 at z ∼ 1.5 at a given stellar mass. We further investigate the evolution with redshift of the specific SFR. Our results are in the upper range of previous measurements, in particular at z ∼ 3, and are consistent with a plateau at 3 < z < 4. Current model predictions (either analytic, semi-analytic or hydrodynamic) are inconsistent with these values, as they yield lower predictions than the observations in the redshift range we explore. We use these results to discuss the star formation histories of galaxies in the framework of the main sequence of star-forming galaxies. Our results suggest that galaxies at high redshift (2.5 < z < 4) stay around 1 Gyr on the main sequence. With decreasing redshift, this time increases such that z = 1 main-sequence galaxies with 10 8 < M ∗ /Mo < 10 10 stay on the main sequence until z = 0

Mid- and Far-infrared Luminosity Functions and Galaxy Evolution from Multiwavelength Spitzer Observations up to z~2.5

[Abridged]We exploit a large homogeneous dataset to derive a self-consistent picture of IR emission based on the time-dependent 24, 15, 12 and 8micron monochromatic and bolometric IR luminosity functions (LF) over the 0<z<2.5 redshift range. Our analysis is based on the combination of data from deep Spitzer surveys in the VVDS-SWIRE and GOODS areas. To our limiting flux of S(24)=400microJy our derived sample in VVDS-SWIRE includes 1494 sources, and 666 and 904 sources brighter than S(24)=80microJy are catalogued in GOODS-S and GOODS-N, respectively, for a total area of ~0.9 square degs. We obtain reliable optical identifications and redshifts, providing us a rich and robust dataset for our luminosity function determination. Based on the multi-wavelength information available, we constrain the LFs at 8, 12, 15 and 24micron. We also extrapolate total IR luminosities from our best-fit to the observed SEDs of each source, and use this to derive the bolometric LF and comoving volume emissivity up to z~2.5. In the 0<z<1 interval, the bolometric IR luminosity density evolves as (1+z)^3.8+/-0.4. Although more uncertain at higher-z, our results show a flattening of the IR luminosity density at z>1. The mean redshift of the peak in the source number density shifts with luminosity: the brighest IR galaxies appear to be forming stars earlier in cosmic time (z>1.5), while the less luminous ones keep doing it at more recent epochs (z~1 for L(IR)<10^11L_sun). Our results suggest a rapid increase of the galaxy IR comoving volume emissivity back to z~1 and a constant average emissivity at z>1. We also seem to find a difference in the evolution rate of the source number densities as a function of luminosity, a downsizing evolutionary pattern similar to that reported from other samples of cosmic sources.Comment: Accepted for pubblicantion in Astronomy and Astrophysic

Submillimeter observations of the J2142-4423 Lya protocluster at z = 2.38

We present observations aimed at exploring both the nature of Lya emitting nebulae (Lya blobs) at z=2.38 and the way they trace large scale structure (LSS), by exploring their proximity to maximum starbursts through submillimeter emission. Our most important objectives are to make a census of associated submillimeter galaxies (SMGs), check their properties, and look for a possible overdensity in the protocluster J2142-4426 at z=2.38. We used the newly commissioned Large APEX Bolometer Camera (LABoCa) on the Atacama Pathfinder EXperiment (APEX) telescope, in its Science Verification phase, to carry out a deep 10'x10' map at 870 micron, and we performed multiple checks of the quality of data processing and source extraction. Our map, the first published deep image, confirms the capabilities of APEX/LABoCa as the most efficient current equipment for wide and deep submm mapping. Twenty-two sources were securely extracted with 870 micron flux densities in the range 3-21 mJy, rms noise 0.8-2.4 mJy, and far-IR luminosities probably in the range ~5-20 x 10(12) Lo. Only one of the four 50 kpc-extended Lya blobs has a secure 870 micron counterpart. The 870 micron source counts in the whole area are marginally higher than in the SHADES SCUBA survey, with a possible over-density around this blob. The majority of the 3.6-24 micron SEDs of the submillimeter sources indicate they are starburst dominated, with redshifts mostly >2. However, there is evidence of a high-z AGN in ~30% of the sources.Comment: 14 pages, 9 figures, accepted for publication in A&A, fixed author lis

Histoire et archéologie du pays de Levroux (Indre). Levroux : Association pour la défense et l’étude du canton de Levroux

ill., cartes, plans, bibliogr. p. 133-136International audienc