A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151

摘要

The active galaxy NGC 4151 has a crucial role as one of only two activegalactic nuclei for which black hole mass measurements based on emission linereverberation mapping can be calibrated against other dynamical methods.Unfortunately, effective calibration requires an accurate distance to NGC 4151,which is currently not available. Recently reported distances range from 4 to29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distancevery uncertain, and the geometry of the galaxy and its nucleus prohibitaccurate measurements using other techniques. Here we report a dust-parallaxdistance to NGC 4151 of $D_A = 19.0^{+2.4}_{-2.6}$ Mpc. The measurement isbased on an adaptation of a geometric method proposed previously using theemission line regions of active galaxies. Since this region is too small forcurrent imaging capabilities, we use instead the ratio of thephysical-to-angular sizes of the more extended hot dust emission as determinedfrom time-delays and infrared interferometry. This new distance leads to anapproximately 1.4-fold increase in the dynamical black hole mass, implying acorresponding correction to emission line reverberation masses of black holesif they are calibrated against the two objects with additional dynamicalmasses.