Odd Radio Circles and their Environment

TL;DR

This paper investigates the properties and environments of Odd Radio Circles, faint diffuse radio emission features, suggesting their formation may be influenced by dense environments or galaxy interactions.

Contribution

It provides the first detailed analysis of the environments of known ORCs, linking their occurrence to galaxy overdensities or companions, and proposing environmental factors in their formation.

Findings

All known ORCs are associated with overdense regions or close companions.

Environmental factors like ambient density or magnetic fields may influence ORC formation.

ORCs are likely related to galaxy interactions or events in dense environments.

Abstract

Odd Radio Circles (ORCs) are unexpected faint circles of diffuse radio emission discovered in recent wide deep radio surveys. They are typically about one arcmin in diameter, and may be spherical shells of synchrotron emission about a million light years in diameter, surrounding galaxies at a redshift of ~0.2-0.6. Here we study the properties and environment of the known ORCs. All three known single ORCs either lie in a significant overdensity or have a close companion. If the ORC is caused by an event in the host galaxy, then the fact that they tend to be in an overdensity, or have a close companion, may indicate that the environment is important in creating the ORC phenomenon, possibly because of an increased ambient density or magnetic field.