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

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.