On the slow quenching of M* galaxies: heavily-obscured AGNs clarify the picture

Abstract

We investigate the connection between X-ray and radio-loud AGNs and the physical properties of their evolved and massive host galaxies, focussing on the mass-related quenching channel followed by ${\mathcal{M}}^{\star }(\simeq 10^{10.6}{M}_{\odot })$ galaxies in the rest-frame NUVrK colour diagram at $0.2<z<0.5$. While our results confirm that (1) radio-loud AGNs are predominantly hosted by already-quenched and very massive ($M_{\ast }>10^{11}{M}_{\odot }$) galaxies, ruling out their feedback as a primary driver of ${\mathcal{M}}^{\star }$ galaxy quenching, we found that (2) X-ray AGNs affected by heavy obscuration of their soft X-ray emission are mostly hosted by ${\mathcal{M}}^{\star }$ galaxies that are in the process of quenching. This is consistent with a quenching scenario that involves mergers of (gas-poor) ${\mathcal{M}}^{\star }$ galaxies $after$ the onset of the quenching process, i.e., a scenario where ${\mathcal{M}}^{\star }$ galaxy mergers are not the cause but rather an aftermath of the quenching mechanism(s). In that respect, we discuss how our results may support a picture where the slow quenching of ${\mathcal{M}}^{\star }$ galaxies happens due to halo-halo mergers along cosmic filaments.

11 pages, 6 figures. Accepted for publication in MNRAS; published version