The role of secular evolution in the black hole growth of narrow-line Seyfert 1 galaxies

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 active galactic nucleus in which the black hole growth is, and has always been, dominated by secular evolution. First, 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–σ plane and speculate about the connection between the NLS1 galaxy properties and their black hole spin.

Black holes in pseudobulges: demography and models

“…They investigated the correlation between bar strength and circumnuclear dust morphology for 75 galaxies finding that in many cases strongly barred galaxies showed structures terminating in a circumnuclear starburst ring at ∼10 pc away from the galactic nucleus. On the other hand, many Narrow Line Seyfert 1 galaxies appear as barred systems and their AGNs are believed to be fuelled via bars (e.g., Crenshaw et al 2003;Orban de Xivry et al 2011). Coelho & Gadotti (2011) recently claimed evidence for double the fraction of AGNs in barred galaxies as compared to unbarred galaxies, at least for low-mass bulges.…”

“…Thus, it is not at all certain that BHs in non-classical bulges should end up obeying similar scaling laws. Orban de Xivry et al (2011), for example, suggest that Narrow Line Seyfert 1 may not be in any special phase of their evolution, but simply are BHs growing slowly due to their specific duty cycle and spin, mainly driven by secular processes in their pseudobulge hosts.…”

“…Perhaps one of the most pressing reason to argue for supplementary routes of BH evolution is the prevalence of pseudobulges hosting BHs (e.g., Hu 2008;Gadotti & Kauffmann 2009;Kormendy et al 2011;Mathur et al 2012;Orban de Xivry et al 2011). "Pseudobulges" are structurally and dynamically different from "classical" bulges and ellipticals, which can also have very low specific angular momentum (e.g., Emsellem et al 2011).…”

Spatially Resolved Spectroscopy of Narrow-line Seyfert 1 Host Galaxies

“…Fernández Lorenzo et al 2012). Orban de Xivry et al (2011) proposed that the nuclear activity in NLS1s might be driven by secular evolution. Based on the gas kinematics and suggested galaxy types, it is possible that secular evolution plays a role in at least some of the five objects studied here.…”

“…Mathur et al 2012;Woo et al 2015;Rakshit et al 2017;Zhou et al 2006). The host galaxies of NLS1s seem to be dominated by secular evolution and show indications of pseudo-bulges (Orban de Xivry et al 2011;Mathur et al 2012). They may thus be similar to inactive galaxies with pseudo-bulges, which have been suggested to be inconsistent with the BH scaling relations (Kormendy et al 2011).…”