Radio Variability in Recently-Quenched Galaxies: The Impact of TDE or AGN Driven Outflows

TL;DR

This study investigates radio variability in recently-quenched galaxies, revealing new outflows or jets with peaked spectra, which influence galaxy evolution by impacting molecular gas and star formation.

Contribution

It provides the first detailed radio spectral analysis of post-starburst galaxies with recent outflow activity, highlighting the role of newly launched jets in galaxy quenching.

Findings

All four galaxies show significant radio brightening over 20 years.

Two galaxies exhibit recent radio flares in the 2-4 GHz band.

The outflows have enough energy to affect molecular gas and star formation.

Abstract

Outflows and jets launched from the nuclei of galaxies emit radio synchrotron emission that can be used to study the impact of accretion energy on the host galaxy. The decades-long baseline now enabled by large radio surveys allows us to identify cases where new outflows or jets have been launched. Here, we present the results of a targeted VLA program observing four post-starburst galaxies that have brightened significantly in radio emission over the past ~20 years. We obtain quasi-simultaneous observations in five bands (1-18 GHz) for each source. We find peaked spectral energy distributions, indicative of self-absorbed synchrotron emission. While all four sources have risen significantly over the past ~20 years in the 1-2 GHz band, two also show clear recent flares in the 2-4 GHz band. These sources are less luminous than typical peaked spectrum radio AGN. It remains unclear whether these sources are low luminosity analogs of the peaked radio AGN from accreted gas, or driven by tidal disruption events with missed optical flares. Regardless of the source of the accreted material, these newly-launched outflows contain sufficient energy to drive the molecular gas outflows observed in post-starburst galaxies and to drive turbulence suppressing star formation.