A Population of z > 2 Far-infrared Herschel-SPIRE-selected Starbursts

Casey, C. M. and Berta, S. and Béthermin, M. and Bock, J. and Bridge, C. and Burgarella, D. and Chapin, E. and Chapman, S. C. and Clements, D. L. and Conley, A. and Conselice, C. J. and Cooray, A. and Farrah, D. and Hatziminaoglou, E. and Ivison, R. J. and le Floc'h, E. and Lutz, D. and Magdis, G. and Magnelli, B. and Oliver, S. J. and Page, M. J. and Pozzi, F. and Rigopoulou, D. and Riguccini, L. and Roseboom, I. G. and Sanders, D. B. and Scott, Douglas and Seymour, N. and Valtchanov, I. and Vieira, J. D. and Viero, M. and Wardlow, J. (2012) A Population of z > 2 Far-infrared Herschel-SPIRE-selected Starbursts. The Astrophysical Journal, 761 (2). p. 139. ISSN 0004-637X

Other (pdf)
1210.4932
Download (4MB)

Abstract

We present spectroscopic observations for a sample of 36 Herschel-SPIRE250-500 μm selected galaxies (HSGs) at 2 <z <5 from theHerschel Multi-tiered Extragalactic Survey. Redshifts are confirmed aspart of a large redshift survey of Herschel-SPIRE-selected sourcescovering ~0.93 deg2 in six extragalactic legacy fields.Observations were taken with the Keck I Low Resolution ImagingSpectrometer and the Keck II DEep Imaging Multi-Object Spectrograph.Precise astrometry, needed for spectroscopic follow-up, is determined byidentification of counterparts at 24 μm or 1.4 GHz using across-identification likelihood matching method. Individual sourceluminosities range from log (L IR/L ⊙) =12.5-13.6 (corresponding to star formation rates (SFRs) 500-9000 M⊙ yr-1, assuming a Salpeter initialmass function), constituting some of the most intrinsically luminous,distant infrared galaxies discovered thus far. We present bothindividual and composite rest-frame ultraviolet spectra and infraredspectral energy distributions. The selection of these HSGs isreproducible and well characterized across large areas of the sky incontrast to most z > 2 HyLIRGs in the literature, which are detectedserendipitously or via tailored surveys searching only for high-zHyLIRGs; therefore, we can place lower limits on the contribution ofHSGs to the cosmic star formation rate density (SFRD) at (7 ± 2)× 10-3 M ⊙yr-1 h 3 Mpc-3 at z ~ 2.5,which is >10% of the estimated total SFRD of the universe fromoptical surveys. The contribution at z ~ 4 has a lower limit of 3× 10-3 M ⊙yr-1 h 3 Mpc-3, gsim20% ofthe estimated total SFRD. This highlights the importance of extremelyinfrared-luminous galaxies with high SFRs to the buildup of stellarmass, even at the earliest epochs.