| We propose to use the EVN, VLBA, GBT and Arecibo to map OH 1720 MHz megamaser emission from the z # 0.25 source,
PKS 1413+135. We will also simultaneously map the other three 18cm OH lines from the same source, in absorption. The
1720 MHz line in PKS 1413+135 is the strongest so far detected in any system, with a luminosity well into the megamaser range
(L # 354L# ). The observations will determine the kinematics of the emitting region and whether the emission arises from a
circumnuclear disk or from a cloud complex distant from the AGN. The spatial structures of the main and satellite lines will be
compared, to model physical conditions in the cloud complex. The two satellite lines are conjugate in this system; a comparison
between the redshifts of the satellite lines at every independent spatial location will thus provide independent constraints on
changes in the fine structure constant, #. The Global array is critical to obtain sufficient spatial resolution (# 8 mas # 20 pc)
to resolve a 100 pc structure at this redshift. |
