Prevalence of Compact Nuclear Radio Emission in Post-Merger Galaxies and its Origin

TL;DR

This study investigates the radio properties of post-merger galaxies, revealing prevalent compact nuclear radio emission, identifying new radio AGN, and exploring their origins and implications for AGN feedback and supermassive black hole binaries.

Contribution

It provides new high-resolution radio observations of post-merger galaxies, identifies new radio AGN and a dual AGN candidate, and assesses future VLBI capabilities for SMBH binary searches.

Findings

89% of post-mergers show compact, nuclear radio emission

14 new radio AGN identified, mostly radio-quiet

Discovery of a dual AGN candidate and implications for AGN feedback

Abstract

Post-merger galaxies are unique laboratories to study the triggering and interplay of star-formation and AGN activity. Combining new, high resolution, 10 GHz Jansky Very Large Array (VLA) observations with archival radio surveys, we have examined the radio properties of 28 spheroidal post-merger galaxies. We find a general lack of extended emission at (sub-)kiloparsec scales, indicating the prevalence of compact, nuclear radio emission in these post-merger galaxies, with the majority (16/18; 89\%) being radio-quiet at 10 GHz. Using multi-wavelength data, we determine the origin of the radio emission, discovering 14 new radio AGN and 4 post-mergers dominated by emission from a population of supernova remnants. Among the radio AGN, almost all are radio-quiet (12/14; 86\%). We discover a new dual AGN (DAGN) candidate, J1511+0417, and investigate the radio properties of the DAGN candidate J0843+3549. 4 of these radio AGN are hosted by SF emission-line galaxies, suggesting that radio AGN activity may be present during periods of SF activity in post-mergers. The low jet powers and compact morphologies of these radio AGN also point to a scenario in which AGN feedback may be efficient in this sample of post-mergers. Lastly, we present simulated, multi-frequency observations of the 14 radio AGN with the Very Long Baseline Array (VLBA) and the VLBI capabilities of the Next Generation Very Large Array (ngVLA) to assess the feasibility of these instruments in searches for supermassive black hole binaries (SMBHBs).