Compact Radio Emission from Nearby Galaxies with Mid-infrared Nuclear Outbursts

TL;DR

This study uses sensitive 5.5 GHz radio observations to detect nuclear radio emission in nearby galaxies with mid-infrared outbursts, suggesting the presence of jets or outflows possibly linked to active galactic nuclei.

Contribution

It provides the first high detection rate of radio emission in MIR-burst galaxies and models the emission as decelerating jets, indicating powerful jets may be common in such galaxies.

Findings

Radio emission detected in 75% of the sample

Most radio sources are compact and unresolved

Results consistent with decelerating jets with energies of 10^{51-52} erg

Abstract

We present 5.5 GHz observations with the VLA of a sample of nearby galaxies with energetic nuclear outbursts at mid-infrared (MIR) bands. These observations reach a uniform depth down to a median rms of ~10 uJy, representing one of most sensitive searches for radio emission associated with nuclear transients. We detect radio emission in 12 out of 16 galaxies at a level of >5sigma, corresponding to a detection rate of 75%. Such a high detection is remarkably different from previous similar searches in stellar tidal disruption events. The radio emission is compact and not resolved for the majority of sources on scales of ~<0.5" (<0.9 kpc at z<0.1). We find the possibility of the star-formation contributing to the radio emission is low, but an AGN origin remains a plausible scenario, especially for sources that show evidence of AGN activity in their optical spectra. If the detections could represent radio emission associated with nuclear transient phenomenon such as jet or outflow, we use the blast wave model by analogy with the GRB afterglows to describe the evolution of radio light curves. In this context, the observations are consistent with a decelerating jet with an energy of ~10^{51-52} erg viewed at 30\degree-60\degree off-axis at later times, suggesting that powerful jets may be ubiquitous among MIR-burst galaxies. Future continuous monitoring observations will be crucial to decipher the origin of radio emission through detections of potential flux and spectral evolution. Our results highlight the importance of radio observations to constrain the nature of nuclear MIR outbursts in galaxies.