The Complex Physics of Dusty Star-forming Galaxies at High Redshifts as Revealed by Herschel and Spitzer
Berta, S.; Magnelli, B.; Lutz, D.; Wuyts, S.; Popesso, P.; Pozzi, F.; Rodighiero, G.; Clements, D. L.; Buat, V.; Burgarella, D.; Wang, L.; Feltre, A.; Franceschini, A.; Bock, J.; Cooray, A.; Farrah, D.; Marchetti, L.; Oliver, S. J.; Page, M. J.; Rigopoulou, D.; Roseboom, I. G.; Symeonidis, M.; Vaccari, M.; Cava, A.; Magdis, G.; Rowan-Robinson, M.; Smith, A. J.; Silva, L.; Scott, Douglas; Lo Faro, B.; Hurley, P.; González Solares, E. A.
Italy, South Africa, Germany, United States, France, Spain, United Kingdom, Canada
Abstract
We combine far-infrared photometry from Herschel (PEP/HerMES) with deep mid-infrared spectroscopy from Spitzer to investigate the nature and the mass assembly history of a sample of 31 luminous and ultraluminous infrared galaxies ((U)LIRGs) at z ~ 1 and 2 selected in GOODS-S with 24 μm fluxes between 0.2 and 0.5 mJy. We model the data with a self-consistent physical model (GRASIL) which includes a state-of-the-art treatment of dust extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (>1 Gyr) stars and, at the same time, to host a moderate ongoing activity of star formation (SFR <= 100 M ⊙ yr-1). The bulk of the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of the sample require a recent starburst superimposed on a quiescent star formation history. We also find discrepancies between our results and those based on optical-only spectral energy distribution (SED) fitting for the same objects; by fitting their observed SEDs with our physical model we find higher extinctions (by ΔA V ~ 0.81 and 1.14) and higher stellar masses (by Δlog(M sstarf) ~ 0.16 and 0.36 dex) for z ~ 1 and z ~ 2 (U)LIRGs, respectively. The stellar mass difference is larger for the most dust-obscured objects. We also find lower SFRs than those computed from L IR using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age stellar populations through "cirrus" emission (~73% and ~66% of the total L IR for z ~ 1 and z ~ 2 (U)LIRGs, respectively).
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.