BLR kinematics and Black Hole Mass in Markarian 6

TL;DR

This study analyzes the BLR kinematics and estimates the black hole mass in Markarian 6 using optical spectral data, revealing a combination of Keplerian and infall motions and confirming the black hole mass through reverberation mapping.

Contribution

First detailed reverberation mapping of Markarian 6's BLR, combining velocity-delay analysis with Monte Carlo simulations to determine black hole mass and kinematic structure.

Findings

BLR lag for Hbeta is 21.1 days, for Halpha about 27 days.

BLR kinematics show signs of Keplerian and infall motions.

Black hole mass estimated at (1.8±0.2)×10^8 solar masses.

Abstract

We present results of the optical spectral and photometric observations of the nucleus of Markarian 6 made with the 2.6-m Shajn telescope at the Crimean Astrophysical Observatory. The continuum and emission Balmer line intensities varied more than by a factor of two during 1992-2008. The lag between the continuum and Hbeta emission line flux variations is 21.1+-1.9 days. For the Halpha line the lag is about 27 days but its uncertainty is much larger. We use Monte-Carlo simulation of the random time series to check the effect of our data sampling on the lag uncertainties and we compare our simulation results with those obtained by random subset selection (RSS) method of Peterson et al. (1998). The lag in the high-velocity wings are shorter than in the line core in accordance with the virial motions. However, the lag is slightly larger in the blue wing than in the red wing. This is a signature of the infall gas motion. Probably the BLR kinematic in the Mrk 6 nucleus is a combination of the Keplerian and infall motions. The velocity-delay dependence is similar for individual observational seasons. The measurements of the Hbeta line width in combination with the reverberation lag permits us to determine the black hole mass, M_BH=(1.8+-0.2)x10^8 M_sun. This result is consistent with the AGN scaling relationships between the BLR radius and the optical continuum luminosity (R_BLR is proportional to L^0.5) as well as with the black-hole mass-luminosity relationship (M_BH-L) under the Eddington luminosity ratio for Mrk 6 to be L_bol/L_Edd ~ 0.01.