The Host Galaxies of Radio AGN: New Views from Combining LoTSS and MaNGA Observations

TL;DR

This study combines radio and optical spectroscopic data to analyze how radio AGN influence their host galaxies' evolution, revealing that AGN activity ionizes surrounding gas and may help maintain galaxy quiescence.

Contribution

It provides new insights by integrating LoTSS and MaNGA data to connect radio AGN properties with galaxy evolution and quenching mechanisms.

Findings

Radio AGN hosts are mostly quiescent galaxies.

Radio AGN activity ionizes the nuclear interstellar medium.

Radio AGN help sustain galaxy quiescence through gas heating.

Abstract

We utilize a combination of radio continuum observations and optical integral field spectroscopic (IFS) data to explore the impact of radio AGN on the evolution of their host galaxies at both global and sub-galactic scales. We construct a comprehensive radio-IFS sample comprising 5548 galaxies with redshift z<0.15 by cross-matching the LoTSS with the MaNGA survey. We revisit the tight linear radio continuum - star formation relation and quantify its intrinsic scatter, then use the relation to classify 616 radio-excess AGN with excessive radio luminosities over that expected from their star formation rate. Massive radio AGN host galaxies are predominantly quiescent systems, but the quenching level shows no correlation with the jet luminosity. The mass assembly histories derived from the stellar population synthesis model fitting agree with the cosmological simulations incorporating radio-mode AGN feedback models. We observe that radio AGN hosts grow faster than a control sample of galaxies matched in stellar mass, and the quenching age ($\sim$5 Gyr) is at larger lookback times than the typical radio jet age (<1 Gyr). By stacking the spectra in different radial bins and comparing results for radio AGN hosts and their controls, we find emission line excess features in the nuclear region of radio AGN hosts. This excess is more prominent in low-luminosity, low-mass, and compact radio AGN. The [NII]/H$\alpha$ ratios of the excessive emission line indicate that radio AGN or related jets are ionizing the surrounding interstellar medium in the vicinity of the nucleus. Our results support the scenario that the observed present-day radio AGN activity may help their host galaxies maintain quiescence through gas ionization and heating, but it is not responsible for the past quenching of their hosts.