| We propose to map the H 2 O megamaser in UGC 3789, discovered with the GBT on 21 December 2005. In combination
with GBT monitoring, we can use this observation to determine a geometric distance to the host galaxy. UGC 3789
is among the best candidates for measuring the extragalactic distance scale using the maser technique because it is
at an appropriate distance (46 Mpc), its maser is rich in bright, narrow features both at systemic and high velocities
(likely identifying a ``clean'' dynamical structure), and the galaxy is situated at a fortuitous, high declination good
for visibility across long baselines. In addition, an acceleration in the systemic features has already been measured
with preliminary GBT spectra and so the determination of the linear size of the disk is assured from an analysis of
the disk dynamics. By comparing the linear size to the angular size available from these VLBI observations we can
determine the distance to the galaxy. This program will serve as a ``proof of concept'' in support of the Key Project
being proposed to determine the equation of state of Dark Energy. |
