Clustering of galaxies around gamma-ray burst sight-lines

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-171 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 KAB 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