A Low-Mass Black Hole in the Nearby Seyfert Galaxy UGC 06728

Abstract

We present the results of a recent reverberation mapping campaign for UGC 06728, a nearby low-luminosity Seyfert 1 in a late-type galaxy. Nightly monitoring in the spring of 2015 allowed us to determine an H${\hat{I}}^2$ time delay of $\ddot{I}„=1.4\pm 0.8$ days. Combined with the width of the variable H${\hat{I}}^2$ line profile, we determine a black hole mass of $M_{\mathrm{BH}}=(7.1\pm 4.0)\times 10^5$ M${}_{\odot }$. We also constrain the bulge stellar velocity dispersion from higher-resolution long slit spectroscopy along the galaxy minor axis and find $\ddot{I}{ƒ}_{\star }=51.6\pm 4.9$ km s${}^{-1}$. The measurements presented here are in good agreement with both the $R_{\mathrm{BLR}}-L$ relationship and the $M_{\mathrm{BH}}-\ddot{I}{ƒ}_{\star }$ relationship for AGNs. Combined with a previously published spin measurement, our mass determination for UGC 06728 makes it the lowest-mass black hole that has been fully characterized, and thus an important object to help anchor the low-mass end of black hole evolutionary models.

accepted for publication in ApJ; 10 pages, 10 figures, 5 tables