NGC 3065: A Certified LINER with Broad, Variable Balmer Lines

Abstract

Motivated by the X-ray properties of the galaxy NGC 3065, we have obtained new optical spectra which reveal that it has a low-ionization nuclear emission-line region (LINER) as well as broad Balmer emission lines, establishing it as an active galactic nucleus. We also examined an older spectrum from the CfA Redshift Survey which, lacking broad Balmer lines, indicates that they appeared some time after 1980. Thus NGC 3065 joins the set of LINERs with broad, variable Balmer lines, which includes such well-known galaxies as NGC 1097 and M81. Inspired by the sometimes double-peaked profiles of the variable Balmer lines in other LINERs, we speculate that the broad Balmer lines of NGC 3065 also come from an accretion disk. We illustrate the plausibility of this hypothesis by fitting a disk model to the observed H$\alpha$ profile. We also estimate the mass of the central black hole as (9+/-4) 10^7 M_sol from the properties of the host galaxy, which leads to the conclusion that the accretion rate is only 2 10^{-4} times the Eddington value, a property that appears to be common among LINERs. At such a low relative accretion rate the inner accretion disk can turn into a vertically-extended ion torus, which can illuminate the outer, thin disk and power the broad-line emission. The reason for the sudden appearance of broad Balmer lines is an open question, although we suggest two possible explanations: tidal disruption of a star or a sudden transition in the structure of the accretion disk.