Nuclear activity in isolated galaxies

Abstract

We present a spectroscopic study of the incidence of active galactic nucleus (AGN) nuclear activity in two samples of isolated galaxies. Our results show that the incidence of nonthermal nuclear activity is about 43 and 31 per cent for galaxies with emission lines and 40 and 27 per cent for the total sample, respectively. For the first time we have a large number of bona fide isolated galaxies (513 objects), with statistically significant number of all morphological types. A large fraction (~70 per cent) of elliptical galaxies or early-type spirals have an AGN and ~70 per cent of them are low-ionization nuclear emission-line regions. We find a larger fraction of AGN in early morphological types, as also found in the general population of galaxies. Only 3 per cent of the AGN show the presence of broad lines (not a single one can be classified as type 1 AGN). This is an important result which is 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 accretion. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.