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

TL;DR

This paper reports a new dust-parallax distance of 19 Mpc to NGC 4151, enabling more accurate black hole mass measurements by calibrating reverberation mapping against dynamical methods.

Contribution

It introduces a novel geometric dust-parallax method for measuring distances to active galaxies, improving black hole mass calibration accuracy.

Findings

Distance to NGC 4151 is 19.0 Mpc with uncertainties.

Black hole mass estimate increases by a factor of 1.4 with the new distance.

Impacts calibration of reverberation mapping techniques.

Abstract

The active galaxy NGC 4151 has a crucial role as one of only two active galactic nuclei for which black hole mass measurements based on emission line reverberation 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 to 29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distance very uncertain, and the geometry of the galaxy and its nucleus prohibit accurate measurements using other techniques. Here we report a dust-parallax distance to NGC 4151 of $D_A = 19.0^{+2.4}_{-2.6}$ Mpc. The measurement is based on an adaptation of a geometric method proposed previously using the emission line regions of active galaxies. Since this region is too small for current imaging capabilities, we use instead the ratio of the physical-to-angular sizes of the more extended hot dust emission as determined from time-delays and infrared interferometry. This new distance leads to an approximately 1.4-fold increase in the dynamical black hole mass, implying a corresponding correction to emission line reverberation masses of black holes if they are calibrated against the two objects with additional dynamical masses.