The Size of the Broad Line Region in M84 (NGC 4374)

TL;DR

This paper estimates the size of the broad line region in galaxy M84, finding it to be unusually large at 7-9 parsecs, which may explain the galaxy's low ionization levels despite hosting a supermassive black hole.

Contribution

The study provides the first measurement of the BLR size in M84, revealing it to be the largest known, and offers insights into the relationship between BLR size and AGN ionization.

Findings

BLR radius in M84 is approximately 7-9 parsecs.

The large BLR size may explain the low ionization in M84.

M84's BLR is the largest measured to date.

Abstract

M84 is a giant elliptical galaxy located in the Virgo cluster. Prior imaging with the Hubble Space Telescope (HST) revealed a small, highly inclined, nuclear ionized gas disk, the kinematics of which indicate the presence of a 0.4 -1.5 billion solar mass black hole. Two prominent radio jets emerge perpendicular to the nuclear ionized gas disk terminating in large radio lobes that extend beyond the visible galaxy. Plausible kinematic models are used to constrain the size of the broad line region (BLR) in M84 by modeling the shape of the broad H-alpha emission line profile. The analysis indicates that the emitting region is large with an outer radius between ~ 7 and 9 pc, depending on whether the kinematic model is represented by a spherically symmetric inflow or a Keplerian disk. The inferred size makes the BLR in M84 the largest yet to be measured. The fact that the BLR in M84 is so large may explain why the AGN is unable to sustain the ionization seen there. Thus, the BLR in M84 is not simply that of a scaled down quasar.