Quasar Host Galaxies and the $M_{SMBH}$ - $\sigma_{*}$ Relation

TL;DR

This study measures super-massive black hole masses in quasars using emission lines, compares the $M_{SMBH}$-$\sigma_{*}$ relation across different quasar types, and examines correlations with radio luminosity and gas-phase metallicity.

Contribution

It provides a detailed analysis of SMBH mass estimation via emission lines and investigates the $M_{SMBH}$-$\sigma_{*}$ relation and radio properties in quasars, challenging the use of [O III] as a stellar velocity dispersion surrogate.

Findings

Good agreement between H$eta$ and H$ extalpha$ derived SMBH masses.

No correlation between radio luminosity and SMBH mass.

Sub-solar gas-phase oxygen abundance in all quasars.

Abstract

We analyze the emission line profiles detected in deep optical spectra of quasars to derive the mass of their super-massive black holes (SMBH) following the single-epoch virial method. Our sample consists in 6 radio-loud quasars and 4 radio-quiet quasars. We carefully fit a broad and narrow Gaussian component for each emission line in both the H$\beta$ (10 objects) and H$\alpha$ regions (5 objects). A very good agreement of the derived SMBH masses, $M_{\rm SMBH}$, is found using the fitted broad H$\beta$ and H$\alpha$ emission lines. We compare our $M_{\rm SMBH}$ results with those found by previous studies. We study the relationship between the $M_{\rm SMBH}$ of the quasar and the stellar velocity dispersion, $\sigma_{*}$, of the host galaxy. We use the measured $M_{\rm SMBH}$ and $\sigma_{*}$ to investigate the $M_{\rm SMBH}$ - $\sigma_{*}$ relation for both the radio-loud and radio-quiet subsamples. Besides the scatter, we find a good agreement between radio-quiet quasars and AGN+quiescent galaxies and between radio-loud quasars and AGN. Our analysis does not support the hypothesis of using $\sigma$([O III] $\lambda$5007) as a surrogate for stellar velocity dispersions in high-mass, high-luminosity quasars. We also investigate the relationship between the 5 GHz radio-continuum luminosity, $L_{\rm~5\,GHz}$, of the quasar host galaxy with both $M_{\rm SMBH}$ and $\sigma_{*}$. We do not find any correlation between $L_{\rm 5\,GHz}$ and $M_{\rm SMBH}$, although we observe a trend that galaxies with larger stellar velocity dispersions have larger $L_{\rm 5\,GHz}$. Using the results of our fitting for the narrow emission lines of [O III] $\lambda$5007 and [N II] $\lambda$6583 we estimate the gas-phase oxygen abundance of six quasars, being sub-solar in all cases.