MIGHTEE: Are giant radio galaxies more common than we thought?

TL;DR

This study reports the discovery of two giant radio galaxies in the COSMOS field using MeerKAT, suggesting that such large structures are more common than previously thought due to earlier observational limitations.

Contribution

The paper demonstrates that MeerKAT's high sensitivity reveals diffuse emission in GRGs, indicating a higher prevalence of these galaxies than previously estimated.

Findings

Two new GRGs discovered with sizes of 2.4 Mpc and 2.0 Mpc.

Detection of diffuse lobe emission previously unresolved in high-resolution surveys.

The probability of finding such large GRGs in a small field is extremely low, implying underestimation in past surveys.

Abstract

We report the discovery of two new giant radio galaxies (GRGs) using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey. Both GRGs were found within a 1 deg^2 region inside the COSMOS field. They have redshifts of z=0.1656 and z=0.3363 and physical sizes of 2.4Mpc and 2.0Mpc, respectively. Only the cores of these GRGs were clearly visible in previous high resolution VLA observations, since the diffuse emission of the lobes was resolved out. However, the excellent sensitivity and uv coverage of the new MeerKAT telescope allowed this diffuse emission to be detected. The GRGs occupy a unpopulated region of radio power - size parameter space. Based on a recent estimate of the GRG number density, the probability of finding two or more GRGs with such large sizes at z<0.4 in a ~1deg^2 field is only 2.7x10^-6, assuming Poisson statistics. This supports the hypothesis that the prevalence of GRGs has been significantly underestimated in the past due to limited sensitivity to low surface brightness emission. The two GRGs presented here may be the first of a new population to be revealed through surveys like MIGHTEE which provide exquisite sensitivity to diffuse, extended emission.