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

TL;DR

This study investigates the clustering of field galaxies near z=0.56 around GRB 021004 using photometric redshifts, absorption lines, and galaxy surveys, revealing a significant inhomogeneity potentially linked to a galaxy cluster.

Contribution

It provides multi-method evidence for a galaxy cluster at z=0.56 near GRB 021004, combining photometric, spectroscopic, and large-scale survey data.

Findings

Photometric redshift peak near z=0.56 in GRB field

Detection of Mg II absorption doublet at z=0.56

Identification of a large-scale galaxy inhomogeneity (~6-8 deg)

Abstract

We test for reliability any signatures of field galaxies clustering in the GRB 021004 line of sight. The first signature is the GRB 021004 field photometric redshifts distribution based on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences observations with a peak near z = 0.56 estimated from multicolor photometry in the GRB direction. The second signature is the Mg II 2796, 2803AA absorption doublet at z = 0.56 in VLT/UVES spectra obtained for the GRB 021004 afterglow. The third signature is the galaxy clustering in a larger (of about 3 sq.deg.) area around GRB 021004 with an effective peak near z = 0.56 for both the spectral and photometric redshifts from a few catalogs of clusters based on the Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS) as a part of SDSS-III. From catalog data the size of the whole inhomogeneity in distribution of the galaxy cluster with the peak near z = 0.56 was also estimated as about 6--8 deg. or 140--190 Mpc. A possibility of inhomogeneity (a galaxy cluster) near the GRB 021004 direction can be also confirmed by an inhomogeneity in cosmic microwave background related with the Sunyaev-Zeldovich effect.