H. Dominguez

Dissecting the cosmic infra-red background with Herschel/PEP

The constituents of the cosmic IR background (CIB) are studied at its peak wavelengths (100 and 160 μm) by exploiting Herschel/PACS observations of the GOODS-N, Lockman Hole, and COSMOS fields in the PACS evolutionary probe (PEP) guaranteed-time survey. The GOODS-N data reach 3σ depths of ∼3.0 mJy at 100 μ ma nd∼5.7 mJy at 160 μm. At these levels, source densities are 40 and 18 beams/source, respectively, thus hitting the confusion limit at 160 μm. Differential number counts extend from a few mJy up to 100-200 mJy, and are approximated as a double power law, with the break lying between 5 and 10 mJy. The available ancillary information allows us to split number counts into redshift bins. At z ≤ 0.5 we isolate a class of luminous sources (LIR ∼ 10 11 L� ), whose SEDs resemble late-spiral galaxies, peaking at ∼130 μm restframe and significantly colder than what is expected on the basis of pre-Herschel models. By integrating number counts over the whole covered flux range, we obtain a surface brightness of 6.36± 1.67 and 6.58± 1.62 [nW m −2 sr −1 ] at 100 and 160 μm, resolving ∼45% and ∼52% of the CIB, respectively. When stacking 24 μm sources, the inferred CIB lies within 1.1σ and 0.5σ from direct measurements in the two bands, and fractions increase to 50% and 75%. Most of this resolved CIB fraction was radiated at z ≤ 1.0, with 160 μm sources found at higher redshift than 100 μm ones.

The star-formation rates of 1.5 < z < 2.5 massive galaxies

The star formation rate (SFR) is a key parameter in the study of galaxy evolution. The accuracy of SFR measurements at z ∼ 2 has been questioned following a disagreement between observations and theoretical models. The latter predict SFRs at this redshift that are typically a factor 4 or more lower than the measurements. We present star-formation rates based on calorimetric measurements of the far-infrared (FIR) luminosities for massive 1.5 12.2 L� . The SFGs and AGNs tend to exhibit the same 24 μm excess. The UV SFRs are in closer agreement with the FIR-based SFRs. Using a Calzetti UV extinction correction results in a mean excess of up to 0.3 dex and a scatter of 0.35 dex from the FIR SFRs. The previous UV SFRs are thus confirmed and the mean excess, while narrowing the gap, is insufficient to explain the discrepancy between the observed SFRs and simulation predictions.

Far-infrared properties of submillimeter and optically faint radio galaxies

We use deep observations obtained with the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel Space Observatory to study the far-infrared (FIR) properties of submillimeter and optically faint radio galaxies (SMGs and OFRGs). From literature we compiled a sample of 35 securely identified SMGs and nine OFRGs located in the GOODS-N and the A2218 fields. This sample is cross-matched with our PACS 100 μm and 160 μm multi-wavelength catalogs based on sources-extraction using prior detections at 24 μm. About half of the galaxies in our sample are detected in at least the PACS 160 μm bandpass. The dust temperatures and the infrared luminosities of our galaxies are derived by fitting their PACS and SCUBA 850 μm (only the upper limits for the OFRGs) flux densities with a single modified (β = 1.5) black body function. The median dust temperature of our SMG sample is Tdust = 36 ± 8 K while for our OFRG sample it is Tdust = 47 ± 3 K. For both samples, median dust temperatures derived from Herschel data agree well with previous estimates. In particular, Chapman et al. (2005, ApJ, 622, 772) found a dust temperature of Tdust = 36± 7K for a large sample of SMGs assuming the validity of the FIR/radio correlation (i.e., q = log 10 (LFIR[W]/L1.4 GHz[W Hz −1 ]/3.75 × 10 12 )). The agreement between our studies confirms that the local FIR/radio correlation effectively holds at high redshift even though we

A FIRST GLIMPSE INTO THE FAR-IR PROPERTIES OF HIGH-z UV-SELECTED GALAXIES: HERSCHEL/PACS OBSERVATIONS OF z ∼ 3 LBGS

We present first insights into the far-IR properties for a sample of IRAC and MIPS 24??m detected Lyman break galaxies (LBGs) at z ~ 3, as derived from observations in the northern field of the Great Observatories Origins Survey (GOODS-N) carried out with the PACS instrument on board the Herschel Space Observatory. Although none of our galaxies are detected by Herschel, we employ a stacking technique to construct, for the first time, the average spectral energy distribution (SED) of infrared luminous LBGs from UV to radio wavelengths. We derive a median IR luminosity of L IR = 1.6 ? 1012 L ?, placing the population in the class of ultra-luminous infrared galaxies (ULIRGs). Complementing our study with existing multi-wavelength data, we put constraints on the dust temperature of the population and find that for their L IR, MIPS-LBGs are warmer than submillimeter-luminous galaxies while they fall in the locus of the L IR-T d relation of the local ULIRGs. This, along with estimates based on the average SED, explains the marginal detection of LBGs in current submillimeter surveys and suggests that these latter studies introduce a bias toward the detection of colder ULIRGs in the high-z universe, while missing high-z ULIRGS with warmer dust.

Herschel deep far-infrared counts through Abell 2218 cluster-lens

Gravitational lensing by massive galaxy clusters allows study of the population of intrinsically faint infrared galaxies that lie below the sensitivity and confusion limits of current infrared and submillimeter telescopes. We present ultra-deep PACS 100 and 160 μm observations toward the cluster lens Abell 2218 to penetrate the Herschel confusion limit. We derive source counts down to a flux density of 1 mJy at 100 μm and 2 mJy at 160 μm, aided by strong gravitational lensing. At these levels, source densities are 20 and 10 beams/source in the two bands, approaching source density confusion at 160 μm. The slope of the counts below the turnover of the Euclidean-normalized differential curve is constrained in both bands and is consistent with most of the recent backwards evolutionary models. By integrating number counts over the flux range accessed by Abell 2218 lensing (0.94−35 mJy at 100 μ ma nd 1.47−35 mJy at 160 μm), we retrieve a cosmic infrared background surface brightness of ∼8.0 and ∼9.9 nW m −2 sr −1 , in the respective bands. These values correspond to 55 ± 24% and 77 ± 31% of DIRBE direct measurements. Combining Abell 2218 results with wider/shallower fields, these figures increase to 62 ± 25% and 88 ± 32% CIB total fractions, resolved at 100 and 160 μm, disregarding the high uncertainties of DIRBE absolute values.

Herschel FIR counterparts of selected Lyα emitters at z ~ 2.2, Fast evolution since z ~ 3 or missed obscured AGNs?

9 paginas, 2 figuras.-- Letter to the Editor.-- Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.-- et al.