The sign of active galactic nucleus quenching in a merger remnant with radio jets

TL;DR

This study examines the AGN activity in the merger remnant Arp 187, revealing signs of past activity despite current quiescence, indicating AGN quenching possibly due to merger-related processes.

Contribution

It provides multi-wavelength evidence of AGN quenching in a merger remnant, highlighting the temporal disconnect between AGN activity and narrow line region emission.

Findings

Optical and infrared signs indicate past AGN activity.

Current radio and X-ray data suggest AGN has been quenched.

Narrow line regions remain visible due to emission time delay.

Abstract

We investigate optical, infrared, and radio active galactic nucleus (AGN) signs in the merger remnant Arp 187, which hosts luminous jets launched in the order of $10^5$ yr ago but whose present-day AGN activity is still unknown. We find AGN signs from the optical BPT diagram and infrared [OIV]25.89 $\mu$m line, originating from the narrow line regions of AGN. On the other hand, Spitzer/IRS show the host galaxy dominated spectra, suggesting that the thermal emission from the AGN torus is considerably small or already diminished. Combining the black hole mass, the upper limit of radio luminosity of the core, and the fundamental plane of the black hole enable us to estimate X-ray luminosity, which gives $<10^{40}$ erg s$^{-1}$. Those results suggest that the AGN activity of Arp 187 has already been quenched, but the narrow line region is still alive owing to the time delay of emission from the past AGN activity.