Odd Radio Circles as supernovae remnants in the intragroup medium

TL;DR

This paper proposes that Odd Radio Circles (ORCs) are supernova remnants in the intragroup medium, estimating their occurrence rate and characteristics based on optical detection data and radio survey sensitivities.

Contribution

It introduces the novel idea that ORCs are intragroup supernova remnants and provides quantitative estimates of their occurrence and observable properties.

Findings

Estimated 5400 intragroup supernovae per million years in local groups.

Predicted detection of about 1.3 supernova remnants per 1000 sq. degrees in radio surveys.

Supernova remnants can resemble known ORCs in size, brightness, and flux at distances up to 3 Mpc.

Abstract

A measurable fraction ($\sim8$ per cent) of recently discovered arcmin-size circular diffuse radio sources termed as Odd Radio Circles or ORCs can be supernovae remnants in the intragroup medium, within the local group and its immediate neighbour groups of galaxies. This estimate is based on the optical detection rate of the intragroup supernovae events in the nearby ($z \sim 0.1-0.2$) galaxy groups. A rate of about 5400 intragroup supernovae per million year is expected within the local and its immediate neighbour groups of galaxies. For a radio detectability period of about $10^{4}$ years, on average 1.3 intragroup medium supernovae remnants per 1000 square degree are expected to be detected in the radio surveys with a sensitivity that led to discovery of ORCs. The angular size, surface brightness and radio flux of the supernova remnants up to a distance of $\sim3$ Mpc in the intragroup medium can be expected to be similar to the five known ORCs. The intragroup supernovae remnants are not residing in the dense and cold interstellar medium of the galaxies but evolving in low density ($10^{-4}-10^{-5}$ cm$^{-3}$) warm medium ($10^{5}-10^{6}$ K) in galactic halos or beyond, and may find their progenitors in the diffuse stellar light associated with various tidal streamers surrounding the Milky-Way and other nearby galaxies.