Nuclear Activity In Isolated Galaxies

TL;DR

This study investigates the prevalence and characteristics of active galactic nuclei in a large, statistically significant sample of isolated galaxies, revealing a high incidence of low-luminosity AGN and challenging the unified model of AGN.

Contribution

It provides the first large-scale spectroscopic analysis of AGN activity in isolated galaxies, highlighting the role of secular evolution over galaxy interactions.

Findings

Approximately 40% of emission-line galaxies host AGN.

About 70% of early-type galaxies have LINERs.

Less than 3% show broad lines, contradicting the unified model.

Abstract

We present a spectroscopic study of the incidence of AGN nuclear activity in two samples of isolated galaxies (Karachentseva, V.E. & Varela, J.). Our results show that the incidence of non-thermal nuclear activity is about 43% and 31% for galaxies with emission lines and for the total sample 40% and 27% respectively. For the first time we have a large number of bona-fide isolated galaxies (513 objects), with statistically significant number of all types. We find a clear relation between bulge mass and the incidence of nuclear activity in the sample with emission lines. This relation becomes flatter when we take into account the complete sample with no emission line galaxies. A large fraction (~70%) of elliptical galaxies or early type spirals have an active galactic nucleus and ~70% of them are LINERs. Only 3% of the AGN show the presence of broad lines (a not a single one can be classified as type 1 AGN). This is a remarkable result which is completely at odds with the unified model even if we consider warped or clumpy tori. Finally, we interpret the large fraction of AGN in isolated galaxies as the result of secular evolution of their supermasive black holes.