Using Herschel PACS and SPIRE observations as part of the HerMES, we explore the far-IR properties of a sample of mid-IR selected starburst dominated ultra-luminous infrared galaxies (ULIRGs) at z ~ 2. We derive robust estimates of infrared luminosit
ies (L_IR) and dust temperatures (Td) of the population and find that galaxies in our sample range from those that are as cold as high-z sub-millimeter galaxies (SMGs) to those that are as warm as optically faint radio galaxies (OFRGs) and local ULIRGs. We also demonstrate that a significant fraction of our sample would be missed from ground based (sub)mm surveys (850-1200{mu}m) showing that the latter introduce a bias towards the detection of colder sources. Similarly, based on PACS data as part of the PEP project, we construct for the first time the full average SED of a sub-sample of infrared luminous Lyman break galaxies at z ~ 3, and find them to have higher T_d when compared to that of SMGs with comparable L_IR. We conclude that high-z ULIRGs span a wide range of dust temperatures, larger than that seen in local ULIRGs, and that Herschel data provide the means to characterize the bulk of the ULIRG population, free from selection biases introduced by ground based (sub)mm surveys.
We study the dust properties of galaxies in the redshift range 0.1<z<2.8 observed by the Herschel Space Observatory in the field of the Great Observatories Origins Deep Survey-North as part of PEP and HerMES key programmes. Infrared (IR) luminosity (
L_IR) and dust temperature (T_dust) of galaxies are derived from the spectral energy distribution (SED) fit of the far-infrared (FIR) flux densities obtained with PACS and SPIRE instruments onboard Herschel. As a reference sample, we also obtain IR luminosities and dust temperatures of local galaxies at z<0.1 using AKARI and IRAS data in the field of the Sloan Digital Sky Survey. We compare the L_IR-T_dust relation between the two samples and find that: the median T_dust of Herschel-selected galaxies at z>0.5 with L_IR>5x10^{10} L_odot, appears to be 2-5 K colder than that of AKARI-selected local galaxies with similar luminosities; and the dispersion in T_dust for high-z galaxies increases with L_IR due to the existence of cold galaxies that are not seen among local galaxies. We show that this large dispersion of the L_IR-T_dust relation can bridge the gap between local star-forming galaxies and high-z submillimeter galaxies (SMGs). We also find that three SMGs with very low T_dust (<20 K) covered in this study have close neighbouring sources with similar 24-mum brightness, which could lead to an overestimation of FIR/(sub)millimeter fluxes of the SMGs.
We present first insights into the far-IR properties for a sample of IRAC and MIPS-24um 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 of infrared luminous LBGs from UV to radio wavelengths. We derive a median IR luminosity of L_{IR} = 1.6 x 10^12 Lo, 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 submm-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 sub-mm surveys and suggests that these latter studies introduce a bias towards the detection of colder ULIRGs in the high-z universe, while missing high-z ULIRGS with warmer dust.
