The Megamaser Cosmology Project: IV. A Direct Measurement of the Hubble Constant from UGC 3789

TL;DR

This paper presents a direct measurement of the Hubble constant using water maser observations in galaxy UGC 3789, achieving an independent estimate with about 10% accuracy, refining previous measurements through extensive VLBI data and modeling.

Contribution

The study provides a more precise, independent measurement of the Hubble constant using megamaser observations, improving upon earlier estimates with enhanced data and modeling techniques.

Findings

H0 = 68.9 +/- 7.1 km/s/Mpc, with 10% uncertainty

Distance to UGC 3789 is 49.6 +/- 5.1 Mpc

Black hole mass is (1.16 +/- 0.12) x 10^7 solar masses

Abstract

In Papers I and II from the Megamaser Cosmology Project (MCP), we reported initial observations of water masers in an accretion disk of a supermassive black hole at the center of the galaxy UGC 3789, which gave an angular-diameter distance to the galaxy and an estimate of Ho with 16% uncertainty. We have since conducted more VLBI observations of the spatial-velocity structure of these water masers, as well as continued monitoring of its spectrum to better measure maser accelerations. These more extensive observations, combined with improved modeling of the masers in the accretion disk of the central supermassive black hole, confirm our previous results, but with signifcantly improved accuracy. We find Ho = 68.9 +/- 7.1 km/s/Mpc; this estimate of Ho is independent of other methods and is accurate to +/-10%, including sources of systematic error. This places UGC 3789 at a distance of 49.6 +/- 5.1 Mpc, with a central supermassive black hole of (1.16 +/- 0.12) x 10^7 Msun.