The Role of Secular Evolution in the Black Hole Growth of Narrow-Line Seyfert 1 Galaxies

TL;DR

This paper investigates how secular evolution influences black hole growth in Narrow-Line Seyfert 1 galaxies, highlighting their unique host galaxy properties and the importance of internal processes over cosmic mergers.

Contribution

It demonstrates that NLS1s are predominantly shaped by secular processes, with their host bulges being pseudo-bulges, and explores implications for black hole growth and galaxy evolution.

Findings

NLS1 host bulges are pseudo-bulges, unlike BLS1 bulges.

Secular processes dominate NLS1 galaxy evolution.

Black hole growth in NLS1s requires several billion years.

Abstract

Narrow-Line Seyfert 1 (NLS1) galaxies show extreme properties with respect to the other Seyfert galaxies. Indeed, they are thought to be accreting at Eddington rates and to possess low mass black holes. Therefore, they may represent a key class of objects for understanding the co-evolution of black holes and their host galaxies. We propose that NLS1s represent a class of AGN in which the black hole growth is, and has always been, dominated by secular evolution. Firstly, by looking at the NLS1 host galaxy properties in the literature, we show that the evolution of NLS1s is presently driven by secular processes, much more so than for Broad-Line Seyfert 1s (BLS1s). Secondly, we study the bulges of NLS1 and BLS1 galaxies. Our results demonstrate that NLS1 host bulges are pseudo-bulges and are statistically different from BLS1 bulges. This difference points to the particular importance of secular processes in the past evolution of their hosts. We build on this result to understand the implications on their evolution and the duration of their duty cycle. We show that NLS1s are not necessarily in a special phase of black hole growth and that several Gyr are required for their black hole masses to become similar to BLS1s. Finally, in the light of our results, we discuss the location of NLS1 galaxies on the MBH-\sigma plane and speculate about the connection between the NLS1 galaxy properties and their black hole spin.