A Revised Broad-Line Region Radius and Black Hole Mass for the Narrow-Line Seyfert 1 NGC 4051

TL;DR

This study provides new reverberation mapping measurements for NGC 4051, refining its BLR radius and black hole mass, and aligning it with established AGN scaling relationships, thus resolving previous outlier status.

Contribution

First high-cadence reverberation mapping campaign for NGC 4051, yielding improved BLR radius and black hole mass estimates consistent with scaling relations.

Findings

BLR radius of 1.87 light days for NGC 4051

Black hole mass estimated at 1.73 million solar masses

Results align NGC 4051 with the R_BLR-L relationship

Abstract

We present the first results from a high sampling rate, multi-month reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from telescopes around the world. The primary goal of this campaign was to obtain either new or improved Hbeta reverberation lag measurements for several relatively low luminosity AGNs. We feature results for NGC 4051 here because, until now, this object has been a significant outlier from AGN scaling relationships, e.g., it was previously a ~2-3sigma outlier on the relationship between the broad-line region (BLR) radius and the optical continuum luminosity - the R_BLR-L relationship. Our new measurements of the lag time between variations in the continuum and Hbeta emission line made from spectroscopic monitoring of NGC 4051 lead to a measured BLR radius of R_BLR = 1.87 (+0.54 -0.50) light days and black hole mass of M_BH = 1.73 (+0.55 -0.52) x 10^6 M_sun. This radius is consistent with that expected from the R_BLR-L relationship, based on the present luminosity of NGC 4051 and the most current calibration of the relation by Bentz et al. (2009a). We also present a preliminary look at velocity-resolved Hbeta light curves and time delay measurements, although we are unable to reconstruct an unambiguous velocity-resolved reverberation signal.