Kinematics of the Broad Line Region in M81

TL;DR

This paper proposes a steady-state spherical inflow model to explain the broad emission lines in M81's nucleus, revealing an unusually large broad line region that impacts the AGN's ionization capacity.

Contribution

It introduces a new inflow-based model for the broad line region in M81, with detailed measurements of its size, mass, and density, differing from typical AGN models.

Findings

Largest measured broad line region (~1 pc) in M81

Inflow rate sufficient for observed luminosity

Low filling factor of ionized gas (~5 x 10^-9)

Abstract

A new model is presented which explains the origin of the broad emission lines observed in the LINER/Seyfert nucleus of M81 in terms of a steady state spherically symmetric inflow, amounting to 1 x 10^-5 Msun/yr, which is sufficient to explain the luminosity of the AGN. The emitting volume has an outer radius of ~1 pc, making it the largest broad line region yet to be measured, and it contains a total mass of ~ 5 x 10^-2 Msun of dense, ~ 10^8 cm^-3, ionized gas, leading to a very low filling factor of ~ 5 x 10^-9. The fact that the BLR in M81 is so large may explain why the AGN is unable to sustain the ionization seen there. Thus, the AGN in M81 is not simply a scaled down quasar.