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

Creators: Casey, C. M.; Bock, J.; Bridge, C.; Cooray, A.; Vieira, J. D.; Viero, M.

Abstract

We present spectroscopic observations for a sample of 36 Herschel-SPIRE 250-500 μm selected galaxies (HSGs) at 2 < z < 5 from the Herschel Multi-tiered Extragalactic Survey. Redshifts are confirmed as part of a large redshift survey of Herschel-SPIRE-selected sources covering ~0.93 deg^2 in six extragalactic legacy fields. Observations were taken with the Keck I Low Resolution Imaging Spectrometer and the Keck II DEep Imaging Multi-Object Spectrograph. Precise astrometry, needed for spectroscopic follow-up, is determined by identification of counterparts at 24 μm or 1.4 GHz using a cross-identification likelihood matching method. Individual source luminosities range from log (L_(IR)/L_☉) = 12.5-13.6 (corresponding to star formation rates (SFRs) 500-9000 M_☉ yr^(–1), assuming a Salpeter initial mass function), constituting some of the most intrinsically luminous, distant infrared galaxies discovered thus far. We present both individual and composite rest-frame ultraviolet spectra and infrared spectral energy distributions. The selection of these HSGs is reproducible and well characterized across large areas of the sky in contrast to most z > 2 HyLIRGs in the literature, which are detected serendipitously or via tailored surveys searching only for high-z HyLIRGs; therefore, we can place lower limits on the contribution of HSGs 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 from optical surveys. The contribution at z ~ 4 has a lower limit of 3 × 10^(–3) M_☉ yr^(–1) h^3 Mpc^(–3), ≳20% of the estimated total SFRD. This highlights the importance of extremely infrared-luminous galaxies with high SFRs to the buildup of stellar mass, even at the earliest epochs.

Additional Information

© 2012 American Astronomical Society. Received 2012 July 20; accepted 2012 October 12; published 2012 December 4. C.M.C. is generously supported by a Hubble Fellowship from Space Telescope Science Institute, grant HST-HF-51268.01-A. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work would not be possible without the hard work and dedication of the Keck Observatory night and day staff; special thanks to Marc Kassis, Luca Rizzi, and Greg Wirth for help and advice while observing. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST-0071048. Spire has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI and Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, and Univ. Sussex (UK); and Caltech, JPL, NHSC, and Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). This research has made use of data from the HerMES project (http://hermes.sussex.ac.uk/). HerMES is a Herschel Key Programme utilizing Guaranteed Time from the Spire instrument team, ESAC scientists, and a mission scientist. HerMES is described in Oliver et al. (2012). The Spire data presented in this paper will be released through the HerMES Database in Marseille, HeDaM (http://hedam.oamp.fr/HerMES).

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