Clustering of galaxies around gamma-ray burst sight-lines

Abstract

There is evidence of an overdensity of strong intervening MgII absorption line systems distributed along the lines of sight toward gamma-ray burst (GRB) afterglows relative to quasar sight-lines. If this excess is real, one should also expect an overdensity of field galaxies around GRB sight-lines, as strong MgII tends to trace these sources. In this work, we test this expectation by calculating the two point angular correlation function of galaxies within 120 (∼470 h −1 71 Kpc at z ∼ 0.4) of GRB afterglows. We compare the gamma-ray burst optical and near-infrared detector (GROND) GRB afterglow sample -one of the largest and most homogeneous samples of GRB fields -with galaxies and active galactic nuclei found in the COSMOS-30 photometric catalog. We find no significant signal of anomalous clustering of galaxies at an estimated median redshift of z ∼ 0.3 around GRB sight-lines, down to K AB < 19.3. This result is contrary to the expectations from the MgII excess derived from GRB afterglow spectroscopy, although many confirmed galaxy counterparts to MgII absorbers may be too faint to detect in our sample -especially those at z > 1. We note that the addition of higher sensitivity Spitzer/IRAC or HST/WFC3 data for even a subset of our sample would increase this survey's depth by several orders of magnitude, simultaneously increasing statistics and enabling the investigation of a much larger redshift space.

The Excess Density of Field Galaxies near z=0.56 around the Gamma-Ray Burst GRB021004 Position

“…In conclusion we would like also to emphasize here that since GRBs are detected at more and more distant cosmological distances with redshifts up to 9.2 [13], this poses additional new questions which are of outmost importance for observational cosmology. What are the redshifts at which the sky distribution of GRBs becomes homogeneous?…”

“…Hereby, all these BTA observations were carried out in the course of the search and study of GRB host galaxies and comparison of their properties with those of all observable galaxies in GRB deep fields. Papers [15,16] describe the methodology of processing and interpretation of these observations, which can be used now in new tasks on the study of distribution of galaxy clusters in GRB directions [13,[17][18][19]. In particular, to study the GRB 021004 field we used the methodology already developed for the BV RI deep field of GRB 000926 (see Table 1), which was investigated with BTA and the results were published [15].…”

“…So, GRB afterglow spectroscopy also can reveal intervening systems along the line of sight. The clustering of galaxies and the clustering around GRB sight-lines are detected and studied in the same manner employed with quasar spectroscopy in many papers already (see [13] and references therein) because GRBs originate at cosmological distances with energy releases of 10 51 -10 53 erg at a range of redshifts between about 0.01 and more than 9.2. And long-duration GRBs are beacons of starforming galaxies (see references in [14]) up to very high redshifts.…”

On the Late-Time Spectral Softening Found in X-Ray Afterglows of Gamma-Ray Bursts

“…Since the redshift is a major parameter in determining the quantitative spectrum especially in a narrow energy range less than two orders of magnitude, we now only interpret the time-resolved spectra of the bursts with known redshifts. This leads to seven bursts in Sudilovsky et al 2013). However, GRBs 080207 is not considered in our spectral fitting.…”

Time Evolution of Flares in GRB 130925a: Jet Precession in a Black Hole Accretion System

“…The source was still detected by BAT two hours after the trigger. The redshift of the burst was z = 0.347 (Vreeswijk et al 2013;Sudilovsky et al 2013).…”