Monitoring AGNs with H\beta\ Asymmetry. I. First Results: Velocity-resolved Reverberation Mapping

TL;DR

This study presents initial results from a long-term project using reverberation mapping to investigate the geometry, kinematics, and potential binary black hole evidence in AGN broad-line regions through velocity-resolved Hβ line analysis.

Contribution

It introduces the MAHA project and reports the first velocity-resolved reverberation mapping results for four AGNs, including new black hole mass measurements and insights into BLR dynamics.

Findings

Velocity-resolved time lags vary among AGNs, indicating diverse BLR structures.

SBS 1518+593 shows signatures consistent with virialized motion.

3C 120's velocity-resolved time lags have evolved over time.

Abstract

We have started a long-term reverberation mapping project using the Wyoming Infrared Observatory 2.3 meter telescope titled "Monitoring AGNs with H\beta\ Asymmetry" (MAHA). The motivations of the project are to explore the geometry and kinematics of the gas responsible for complex H\beta\ emission-line profiles, ideally leading to an understanding of the structures and origins of the broad-line region (BLR). Furthermore, such a project provides the opportunity to search for evidence of close binary supermassive black holes. We describe MAHA and report initial results from our first campaign, from December 2016 to May 2017, highlighting velocity-resolved time lags for four AGNs with asymmetric H\beta\ lines. We find that 3C 120, Ark 120, and Mrk 6 display complex features different from the simple signatures expected for pure outflow, inflow, or a Keplerian disk. While three of the objects have been previously reverberation mapped, including velocity-resolved time lags in the cases of 3C 120 and Mrk 6, we report a time lag and corresponding black hole mass measurement for SBS 1518+593 for the first time. Furthermore, SBS 1518+593, the least asymmetric of the four, does show velocity-resolved time lags characteristic of a Keplerian disk or virialized motion more generally. Also, the velocity-resolved time lags of 3C 120 have significantly changed since previously observed, indicating an evolution of its BLR structure. Future analyses of the data for these objects and others in MAHA will explore the full diversity of H\beta\ lines and the physics of AGN BLRs.