New light on gamma-ray burst host galaxies with Herschel^⋆,⋆⋆

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: hunt@arcetri.astro.it
² INAF – IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
³ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, 9000 Gent, Belgium
⁴ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁵ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁶ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, 85748 Garching bei München, Germany
⁷ Physics Department, University of Calabria, via P. Bucci, 87036 Rende (CS), Italy
⁸ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁹ INAF/Osservatorio Astronomico di Brera, via Emilio Bianchi 46, 23807 Merate (LC), Italy
¹⁰ ASI Science Data Centre, via Galileo Galilei, 00044 Frascati (RM), Italy
¹¹ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy
¹² Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomia s/n, 1008 Granada, Spain
¹³ Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu – CNRS – Université Paris Diderot, CE-Saclay, pt courrier 131, 91191 Gif-sur-Yvette, France
¹⁴ Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris 06, 98bis boulevard Arago, 75014 Paris, France
¹⁵ GEPI-Observatoire de Paris, CNRS UMR 8111, Univ. Paris-Diderot, 5 place Jules Jannsen, 92190 Meudon, France

Received: 26 December 2013
Accepted: 13 February 2014

Abstract

Until recently, dust emission has been detected in very few host galaxies of gamma-ray bursts (GRBHs). With Herschel, we have now observed 17 GRBHs up to redshift z ~ 3 and detected 7 of them at infrared (IR) wavelengths. This relatively high detection rate (41%) may be due to the composition of our sample which at a median redshift of 1.1 is dominated by the hosts of dark GRBs. Although the numbers are small, statistics suggest that dark GRBs are more likely to be detected in the IR than their optically bright counterparts. Combining our IR data with optical, near-infrared, and radio data from our own datasets and from the literature, we have constructed spectral energy distributions (SEDs) which span up to 6 orders of magnitude in wavelength. By fitting the SEDs, we have obtained stellar masses, dust masses, star-formation rate (SFR), and extinctions for our sample galaxies. We find that GRBHs are galaxies that tend to have a high specific SFR (sSFR), and like other star-forming galaxies, their ratios of dust-to-stellar mass are well correlated with sSFR. Dust masses of GRBHs relative to stellar mass and SFR fall within the range of other star-forming galaxies in the local universe, and of sub-millimeter galaxies (SMGs) and luminous IR galaxies for redshift z ≳ 1. We incorporate our Herschel sample into a larger compilation of GRBHs, after checking for consistency in mass and SFR estimations. This combined sample is compared to SFR-weighted median stellar masses of the widest, deepest galaxy survey to date in order to establish whether or not GRBs can be used as an unbiased tracer of cosmic comoving SFR density (SFRD) in the universe. In contrast with previous results, this comparison shows that GRBHs are medium-sized galaxies with relatively high sSFRs, as might be expected for galaxies selected on the basis of SFR because of the explosive GRB event. Stellar masses and sSFRs of GRBHs as a function of redshift are similar to what is expected for star-forming galaxy populations atsimilar redshifts. We conclude that there is no strong evidence that GRBs are biased tracers of SFRD; thus they should be able to reliably probe the SFRD to early epochs.