Chengyu Kuo, James A. Braatz, Mark J. Reid, Fred K. Y. Lo, James J. Condon, Caterina M. V. Impellizzeri, Christian Henkel
We present the first direct measurement of the angular-diameter distance with H2O megamaser technique to a galaxy beyond 100 Mpc in a single step without any local calibration. We image the sub-parsec scale H2O maser disk at the center of NGC 6264 with four tracks of Very Long Baseline Interferometry (VLBI) observations. We presented an image from two of these tracks in MCP Paper III, and we add two new tracks here. With the 2.3 years of monthly Green Bank Telescope observations of the H2O emissions in NGC 6264, we measure the centripetal accelerations of the maser lines from the accretion disk by tracking the line-of-sight velocity of each maser component as they change with time. The measured accelerations suggest that the maser disk appears to have more substructure than the masers in UGC 3789 and NGC 4258. In order to model the more complex maser disk properly and determine a precise distance and Hubble constant, we adopt a Bayesian modeling program that fits the maser disk in three dimensions. By assuming the masers follow circular orbits around the central black hole, the best fit of the data gives an angular-diameter distance of 137+/-19 Mpc, a Hubble constant of Ho = 74+/-10 km/s/Mpc, and a mass of the central black hole of (2.89+/-0.39)x10^7 Msun. The result shown in this paper demonstrates the feasibility of the megamaser technique for measuring distances to galaxies deep in the Hubble flow.
View original:
http://arxiv.org/abs/1207.7273
No comments:
Post a Comment