Giant radio galaxies - II. Tracers of large-scale structure

TL;DR

This study uses optical spectroscopy and radio imaging of giant radio galaxies to explore their surrounding large-scale structures, revealing environmental influences on their morphology and growth in the cosmic web.

Contribution

It provides new insights into the environments of giant radio galaxies and their interaction with the large-scale structure of the universe.

Findings

Mean galaxy overdensity near GRGs is ~70.

Lobes tend to be deflected away from overdense regions.

Lobes grow preferentially perpendicular to dense environments.

Abstract

We have carried out optical spectroscopy with the Anglo-Australian Telescope for 24,726 objects surrounding a sample of 19 Giant Radio Galaxies (GRGs) selected to have redshifts in the range 0.05 to 0.15 and projected linear sizes from 0.8 to 3.2 Mpc. Such radio galaxies are ideal candidates to study the Warm-Hot Intergalactic Medium (WHIM) because their radio lobes extend beyond the ISM and halos of their host galaxies, and into the tenuous IGM. We were able to measure redshifts for 9,076 galaxies. Radio imaging of each GRG, including high-sensitivity, wideband radio observations from the Australia Telescope Compact Array for 12 GRGs and host optical spectra (presented in a previous paper, Malarecki et al. 2013), is used in conjunction with the surrounding galaxy redshifts to trace large-scale structure. We find that the mean galaxy number overdensity in volumes of ~700 Mpc$^3$ near the GRG host galaxies is ~70 indicating an overdense but non-virialized environment. A Fourier component analysis is used to quantify the anisotropy in the surrounding galaxy distribution. For GRGs with radio components offset from the radio axis, there is a clear influence of the environment with lobes appearing to be deflected away from overdensities in the surrounding medium. Furthermore, the GRG lobes tend to be normal to the plane defined by the galaxy neighbourhood close to the host. This indicates the tendency for lobes to grow to giant sizes in directions that avoid dense regions on both small and large scales.