GRB 130606A AS A PROBE OF THE INTERGALACTIC MEDIUM AND THE INTERSTELLAR MEDIUM IN A STAR-FORMING GALAXY IN THE FIRST Gyr AFTER THE BIG BANG

Abstract

We present high signal-to-noise ratio Gemini and MMT spectroscopy of the optical afterglow of the gamma-ray burst (GRB) 130606A at redshift z=5.913, discovered by Swift. This is the first high-redshift GRB afterglow to have spectra of comparable quality to those of z ≈ 6 quasars. The data exhibit a smooth continuum at near-infrared wavelengths that is sharply cut off blueward of 8410Å due to absorption from Lyα at redshift z ≈ 5.91, with some flux transmitted through the Lyα forest between 7000−7800Å. We use column densities inferred from metal absorption lines to constrain the metallicity of the host galaxy between a lower limit of [Si/H] −1.7 and an upper limit of [S/H] −0.5 set by the non-detection of S II absorption. We demonstrate consistency between the dramatic evolution in the transmission fraction of Lyα seen in this spectrum over the redshift range z = 4.9 to 5.85 with that previously measured from observations of high-redshift quasars. There is an extended redshift interval of ∆z=0.12 in the Lyα forest at z=5.77 with no detected transmission, leading to a 3σ upper limit on the mean Lyα transmission fraction of 0.2% (or τ eff GP (Lyα)>6.4). This is comparable to the lowest-redshift Gunn-Peterson troughs found in quasar spectra. Some Lyβ and Lyγ transmission is detected in this redshift window, indicating that it is not completely opaque, and hence that the IGM is nonetheless mostly ionized at these redshifts. We set a 2σ upper limit of 0.11 on the neutral fraction of the IGM at the redshift of the GRB from the lack of a Lyα red damping wing, assuming a model with a constant neutral density. GRB 130606A thus for the first time realizes the promise of GRBs as probes of the first galaxies and cosmic reionization.

Constraints on the star formation efficiency of galaxies during the epoch of reionization

“…10). The limits on the IGM neutrality inferred from the measurements of quasar near zones (open hexagon, Mortlock et al 2011) and the GRB damping wings (open circle, Chornock et al 2013) are also shown in the left panel of Fig. 10.…”

“…Attempts have also been made to measure the ionization state of the IGM directly. Reionization is relatively wellconstrained to be completed at z 6 by analysis of the Gunn-Peterson effect (Gunn & Peterson 1965) in the spectra of high-redshift QSOs (e.g., Fan et al 2006;Willott et al 2007;Bolton et al 2011;McGreer et al 2015) and gammaray bursts (GRBs, e.g., Chornock et al 2013). Preliminary measurements of the IGM neutral fraction at z ∼ 7-8 have been made using the Lyα emission fraction of star-forming galaxies (e.g., Stark et al 2010;Treu et al 2013;Pentericci et al 2014;Tilvi et al 2014;Faisst et al 2014;Schenker et al 2014).…”

A VLA Study of High-redshift GRBs. I. Multiwavelength Observations and Modeling of GRB 140311A

“…The large luminosities of GRB afterglows make these energetic events premier probes of the high-redshift universe, ranging from the parsec-scale environments of the progenitors to the properties of the intergalactic medium (Totani et al 2006;Inoue et al 2007;Tanvir et al 2009;Wang et al 2012;Chornock et al 2013Chornock et al , 2014. Additionally, high-redshift GRBs have been speculated to possibly differ from lower redshift events in their energy scales, durations, and circumburst media (Fryer et al 2001;Bromm et al 2003;Heger et al 2003;Suwa & Ioka 2011;Toma et al 2011).…”

On the mass–metallicity relation, velocity dispersion, and gravitational well depth of GRB host galaxies

“…Damped Lyman-α (DLA) absorption line systems which arise in the GRB host galaxies can be observed out to very high redshifts (e.g. Sparre et al (2014) analyse the DLA system at z ∼ 5 in the GRB 111008A afterglow spectrum and Chornock et al (2014) obtain metallicity contraints of GRB 140515A at z = 6.33) and their metallicity can be measured accurately from absorption lines which arise in the ISM. Since GRB afterglows are transients one can study the host galaxy properties later when the GRB afterglows have faded away.…”