Black Hole Mass Estimation in Type 1 AGN: Hβ vs. Mg II Lines and the Role of Balmer Continuum

Jelena Kovačević-Dojčinović,Luka Č Popović,Sladjana Marčeta-Mandić

doi:10.3389/fspas.2017.00007

Jelena Kovačević-Dojčinović, Luka Č Popović + Show 1 more

Open Access

https://doi.org/10.3389/fspas.2017.00007

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Abstract

Here we investigate the H$\beta$ and Mg II spectral line parameters used for the black hole mass (M$_{\rm BH}$) estimation for a sample of Type 1 Active Galactic Nuclei (AGN) spectra selected from the Sloan Digital Sky Survey (SDSS) database. We have analyzed and compared the virialization of the H$\beta$ and Mg II emission lines, and found that the H$\beta$ line is more confident virial estimator than Mg II. We have investigated the influence of the Balmer continuum emission to the M$_{\rm BH}$ estimation from the UV parameters, and found that the Balmer continuum emission can contribute to the overestimation of the M$_{\rm BH}$ on average for ~ 5% (up to 10%).

Highlights

Several methods are used to estimate central black hole (BH) mass MBH in galaxies
The virial methods are based on the assumption that the Broad Line Region (BLR) gas is bounded to the central BH and the main broadening mechanism of the broad emission lines (BELs) is the Keplerian motion around the supermassive BH, so the full width at half maximum (FWHM) of BELs indicates the velocity of the emitting gas
If the emission gas in the BLR is virialized, one can expect to observe correlations between the widths and the gravitational redshifts of the BELs, which comes from the equations for the MBH estimation by the virial method using the line width

Summary

INTRODUCTION

Several methods are used to estimate central black hole (BH) mass MBH in galaxies (for review see e.g., Marziani and Sulentic, 2012; Shen, 2013; Ilicand Popovic, 2014; Peterson, 2014). An alternative method for MBH estimation using the BEL parameters is based on the gravitational redshift in the broad line profiles (see Zheng and Sulentic, 1990; Popovicet al., 1995; Bon et al, 2015; Jonicet al., 2016; Liu et al, 2017). The advantage of this method is that it does not depend on the BLR inclination, unlike the virial methods. We analyze the virialization assumption for the Hβ and Mg II broad lines, and the influence of the Balmer continuum to the MBH estimation from the UV parameters

THE SAMPLE AND ANALYSIS

The Balmer Continuum Model

Measuring the Spectral Parameters

Testing the Virialization of the Broad Hβ and Mg II Lines

CONCLUSIONS