Stability of the Broad Line Region Geometry and Dynamics in Arp 151 Over Seven Years

TL;DR

This study models the broad line region in Arp 151 over seven years, revealing a stable disk-like geometry with increasing size and inflow-dominated dynamics, leading to a consistent black hole mass estimate.

Contribution

It provides the first long-term modeling of BLR geometry and dynamics in Arp 151, demonstrating stability in structure and quantifying growth and inflow over seven years.

Findings

BLR geometry is a stable thick disk over seven years.

BLR size increases by a factor of approximately 2.

Black hole mass estimate is consistent across datasets.

Abstract

The Seyfert 1 galaxy Arp 151 was monitored as part of three reverberation mapping campaigns spanning $2008-2015$. We present modeling of these velocity-resolved reverberation mapping datasets using a geometric and dynamical model for the broad line region (BLR). By modeling each of the three datasets independently, we infer the evolution of the BLR structure in Arp 151 over a total of seven years and constrain the systematic uncertainties in non-varying parameters such as the black hole mass. We find that the BLR geometry of a thick disk viewed close to face-on is stable over this time, although the size of the BLR grows by a factor of $\sim 2$. The dynamics of the BLR are dominated by inflow and the inferred black hole mass is consistent for the three datasets, despite the increase in BLR size. Combining the inference for the three datasets yields a black hole mass and statistical uncertainty of $\log_{10}($M$_{\rm BH}/\rm{M}_{\odot})=6.82^{+0.09}_{-0.09}$ with a standard deviation in individual measurements of 0.13 dex.