Co-evolution of Galaxies and Central Black Holes: Observational Evidence on the Trigger of AGN Feedback

TL;DR

This study presents observational evidence linking extended emission line regions around quasars to galaxy properties and AGN activity, supporting the role of AGN feedback in galaxy and black hole co-evolution.

Contribution

It provides a comprehensive compilation and analysis of EELR measurements, revealing correlations with AGN properties and galaxy characteristics, highlighting the role of gas availability and mergers in EELR formation.

Findings

EELR correlates with Eddington ratio and PC 1 of AGN emission.

EELR is associated with gas-rich, massive blue galaxies.

EELR quasars are found in the massive blue corner of the green valley.

Abstract

A comprehensive analysis of extended emission line region (EELR) around quasars is presented. New Subaru/Suprime-Cam observation is combined with literature search, resulting in a compilation of 81 EELR measurements for type-1 and type-2 quasars with associated active galactic nucleus (AGN) and host galaxy properties. It is found that EELR phenomenon shows clear correlation with Eddington ratio, which links EELR to the constituents of the principal component 1 (PC 1), or eigenvector 1, of the AGN emission correlations. We also find that EELR is preferentially associated with gas-rich, massive blue galaxies. It supports the idea that the primary determinant of EELR creation is the gas availability and that the gas may be brought in by galaxy merger triggering the current star formation as well as AGN activity, and also gives an explanation for the fact that most luminous EELR is found around radio-loud sources with low Eddington ratio. By combining all the observations, it is suggested that EELR quasars occupy the massive blue corner of the green valley, the AGN realm, on the galaxy color - stellar mass diagram. Once a galaxy is pushed to this corner, activated AGN would create EELR by the energy injection into the interstellar gas and eventually blow it away, leading to star-formation quenching. The results presented here provide a piece of evidence for the presence of such AGN feedback process, which may be playing a leading role in the co-evolution of galaxies and central super-massive black holes.