Supermassive black holes, pseudobulges, and the narrow-line Seyfert 1 galaxies

TL;DR

This study uses HST/ACS imaging to analyze the host galaxies of narrow-line Seyfert 1 nuclei, revealing that many have pseudobulges and that black hole growth in these galaxies is likely driven by secular processes rather than mergers.

Contribution

It provides new evidence that NLS1 galaxies often host pseudobulges and suggests black hole growth in these systems occurs through secular evolution, challenging merger-driven models.

Findings

Many NLS1 host galaxies have pseudobulges.

All studied galaxies lie below the standard black hole--bulge luminosity relation.

Black hole growth in NLS1s is likely governed by secular processes.

Abstract

We present HST/ACS observations of ten galaxies that host narrow-line Seyfert 1 (NLS1) nuclei, believed to contain relatively smaller mass black holes accreting at high Eddington ratios. We deconvolve each ACS image into a nuclear point source (AGN), a bulge, and a disk, and fitted the bulge with a Sersic profile and the disk with an exponential profile. We find that at least five galaxies can be classified as having pseudobulges. All ten galaxies lie below the \mbh--L$_{bulge}$ relation, confirming earlier results. Their locus is similar to that occupied by pseudobulges. This leads us to conclude that the growth of BHs in NLS1s is governed by secular processes rather than merger-driven. Active galaxies in pseudobulges point to an alternative track of black hole--galaxy co-evolution. Because of the intrinsic scatter in black hole mass--bulge properties scaling relations caused by a combination of factors such as the galaxy morphology, orientation, and redshift evolution, application of scaling relations to determine BH masses may not be as straightforward as has been hoped.