First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151

TL;DR

This paper reports the first black hole mass measurement in Arp 151 using reverberation mapping from a dedicated spectroscopic campaign, revealing detailed gas dynamics in the broad line region.

Contribution

It provides the first reverberation-based black hole mass measurement for Arp 151 and demonstrates velocity-resolved lag analysis revealing infalling gas.

Findings

Black hole mass in Arp 151 is approximately 7.1 million solar masses.

Hbeta emission line lag measured at about 4.25 days.

Velocity-resolved lag indicates infalling gas in the broad line region.

Abstract

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7 M_sun. We present here the first results from this project -- the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hbeta lag measurement in this object of 4.25(+0.68/-0.66) days in the observed frame. Coupled with the width of the Hbeta emission line in the variable spectrum, we determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hbeta emission line which clearly shows infalling gas in the Hbeta-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.