The Activity of the Neighbours of AGN and Starburst Galaxies: Towards an evolutionary sequence of AGN activity

TL;DR

This study investigates the role of close galaxy interactions in triggering AGN and starburst activity, revealing that neighboring galaxies often show enhanced activity and suggesting an evolutionary sequence from starburst to Seyfert types.

Contribution

It provides new observational evidence linking neighbor galaxy activity to AGN evolution, emphasizing the importance of interactions in galaxy activity progression.

Findings

Over 70% of neighboring galaxies show enhanced activity.

Neighbours of Sy2 galaxies are more ionized and have younger starbursts than those of Sy1.

Results support a sequence from starburst to Sy2 to Sy1 driven by interactions.

Abstract

We present a follow-up study of a series of papers concerning the role of close interactions as a possible triggering mechanism of the activity of AGN and starburst (SB) galaxies. We have already studied the close (<100 kpc) and the large scale (<1 Mpc) environment of Sy1, Sy2 and Bright IRAS galaxies and their respective control samples (Koulouridis et al.). The results led us to the conclusion that a close encounter appears capable of activating a sequence where a normal galaxy becomes first a starburst, then a Sy2 and finally a Sy1 galaxy. However since both galaxies of an interacting pair should be affected, we present here optical spectroscopy and X-ray imaging of the neighbouring galaxies around our Seyfert and BIRG galaxy samples. We find that more than 70% of all neighbouring galaxies exhibit thermal or/and nuclear activity (namely enhanced star formation, starbursting and/or AGN) and furthermore we discovered various trends regarding the type and strength of the neighbour's activity with respect to the activity of the central galaxy, the most important of which is that the neighbours of Sy2 are systematically more ionized, and their straburst is younger, than the neighbours of Sy1s. Our results not only strengthen the link between close galaxy interactions and activity but also provide more clues regarding the evolutionary sequence inferred by previous results.