The black hole mass -- stellar velocity dispersion correlation: bulges versus pseudobulges

TL;DR

This study compares the black hole mass and stellar velocity dispersion relation in different galaxy types, revealing significant differences between bulges and pseudobulges, which suggest distinct formation and growth histories for SMBHs.

Contribution

It provides the first detailed comparison of the $M_{bh}$-$\sigma_*$ relation in bulges versus pseudobulges, highlighting their different slopes and implications for galaxy evolution theories.

Findings

The $M_{bh}$-$\sigma_*$ relation differs significantly between bulges and pseudobulges.

The relation for pseudobulges has a steeper slope, indicating different growth mechanisms.

Core elliptical galaxies show a steeper slope, possibly due to dissipationless mergers.

Abstract

We investigate the correlation between the supermassive black holes (SMBHs) mass ($M_{\rm bh}$) and the stellar velocity dispersion ($\sigma_*$) in two types of host galaxies: the early-type bulges (disk galaxies with classical bulges or elliptical galaxies) and pseudobulges. In the form $\log (M_{\rm bh}/{\rm M_\odot})=\alpha+\beta\log(\sigma_*/200 {\rm km s^{-1}})$, the best-fit results for the 39 early-type bulges are the slope $\beta=4.06\pm0.28$ and the normalization $\alpha=8.28\pm0.05$; the best-fit results for the 9 pseudobulges are $\beta=4.5\pm1.3$, $\alpha=7.50\pm0.18$. Both relations have intrinsic scatter in $\log M_{\rm bh}$ of $\lesssim$0.27 dex. The $M_{\rm bh}$-$\sigma_*$ relation for pseudobulges is different from the relation in the early-type bulges over the 3$\sigma$ significance level. The contrasting relations indicate the formation and growth histories of SMBHs depend on their host type. The discrepancy between the slope of the $M_{\rm bh}$-$\sigma_*$ relations using different definition of velocity dispersion vanishes in our sample, a uniform slope will constrain the coevolution theories of the SMBHs and their host galaxies more effectively. We also find the slope for the ``core'' elliptical galaxies at the high mass range of the relation appears steeper ($\beta\simeq$ 5-6), which may be the imprint of their origin of dissipationless mergers.