GAMMA-RAY BURSTS TRACE UV METRICS OF STAR FORMATION OVER 3 <z< 5

Abstract

-We present the first uniform treatment of long duration gamma-ray burst (GRB) host galaxy detections and upper limits over the redshift range 3 < z < 5, a key epoch for observational and theoretical efforts to understand the processes, environments, and consequences of early cosmic star formation. We contribute deep imaging observations of 13 GRB positions yielding the discovery of eight new host galaxies. We use this dataset in tandem with previously published observations of 31 further GRB positions to estimate or constrain the host galaxy rest-frame ultraviolet (UV; λ = 1600Å) absolute magnitudes M UV . We then use the combined set of 44 M UV estimates and limits to construct the M UV luminosity function (LF) for GRB host galaxies over 3 < z < 5 and compare it to expectations from Lyman break galaxy (LBG) photometric surveys with the Hubble Space Telescope. Adopting standard prescriptions for the luminosity dependence of galaxy dust obscuration (and hence, total star formation rate), we find that our LF is compatible with LBG observations over a factor of 600× in host luminosity, from M UV = −22.5 mag to > −15.6 mag, and with extrapolations of the assumed Schechter-type LF well beyond this range. We review proposed astrophysical and observational biases for our sample, and find they are for the most part minimal. We therefore conclude, as the simplest interpretation of our results, that GRBs successfully trace UV metrics of cosmic star formation over the range 3 < z < 5. Our findings suggest GRBs are providing an accurate picture of star formation processes from z ≈ 3 out to the highest redshifts.

GRB hosts through cosmic time

“…In absence of further secondary environmental factors, GRB hosts would then provide an extensive picture of high-redshift, star-forming galaxies. This conclusion is similar to the one reached through studying metallicities of GRB-DLAs (Fynbo et al 2008;Arabsalmani et al 2015), the UV-luminosity function at a similar redshift (Jakobsson et al 2005;Schulze et al 2015;Greiner et al 2015a), cosmological simulations (Chisari et al 2010) or modeling the mass distribution of GRB hosts (Kocevski et al 2009). …”

“…Because the metallicity of star-forming galaxies in general is decreasing, GRBs are expected to form also more frequently in the most luminous galaxies. Therefore, we expect GRB hosts at high redshift to represent star-forming galaxies much better than at z < 1 (see also Greiner et al 2015a;Perley et al 2015c).…”

Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of theSwift/BAT6 complete sample of bright LGRBs

“…In the future we will move our analysis towards higher redshifts with the aim of obtaining a deeper insight into the condition affecting the rate of LGRBs to confirm if, as suggested by recent studies (Greiner et al 2015;Perley et al 2016b), LGRBs become direct SFR tracers as we move back through cosmic time. Relation between metallicity and stellar-to-gas mass ratio.…”

“…Kistler et al 2008;Robertson & Ellis 2012;Perley et al 2016a;Greiner et al 2015). LGRB host galaxies can be used as a complementary means to standard surveys of star-forming galaxies in order to understand galaxy properties and their evolution throughout cosmic history (e.g.…”

“…At high redshifts very few galaxies are used in analyses, which is presumably the reason why the conclusions drawn from different unbiased samples still differ: while some studies (Greiner et al 2015;Perley et al 2016b) claimed that LGRB hosts can be direct tracers of star formation at about z > 3, others find the hosts to be of low luminosity with a metallicitydependent efficiency (Schulze et al 2015).…”