Measuring the Extragalactic Distance Scale


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.

Name Other * Institution Email Phone
Jim Braatz PI NRAO - CV work: 434-296-0251 home: 434 973-4453
* PI = Principal Investigator; CO = Contact author; T = Thesis observations; S = Student

Front Ends
Gregorian K(18.0 to 26.5 GHz)

Back Ends
VLBA recorder and DAR

Type of Observing

Switching Type

Processor (correlator)

Allotted time 24.00 hours

NRAO Home   |   Contact   |   Directories
Updated 09/19/2007