Showing papers by "Anthony Lasenby published in 1989"

H I absorption measurements over the Galactic center Radio Arc region

Abstract: The compact array of the VLA was used to study H I absorption in a 100-pc region in the center of the Galaxy. An absence of gas was observed at 40-50 km/s across the Radio Arc, suggesting that the '40 km/s molecular cloud' possibly associated with Sgr A is placed behind the Arc. At +20 km/s, the observations show absorption by material which could be depolarizing much of the synchrotron emission from the Arc filaments. The kinematic structure revealed by high-resolution molecular and radio recombination line observations is confirmed by the distribution of H I gas at -10 to -60 km/s.

HI Absorption Against the 40 km s-1 Cloud and the Circum-Nuclear Disk in Sgr A

Abstract: HI absorption studies of the Sgr A complex based upon recent VLA2 observations, show that the 40kms-1 molecular cloud lies behind the Sgr A West region, and that the cloud may be physically associated with the Sgr A East non-thermal shell. The absorbing gas over the range +30 to +60kms-1 lies mainly between the eastern edge of the Sgr A East shell and the western boundary of a cluster of HII regions. There is a pronounced velocity gradient over this region, and at 40kms-1 similar morphology is apparent between the distribution of atomic hydrogen and the edge of the Sgr A East shell. The physical association of the 40kms-1 cloud and the Sgr A East shell, and the placing of the 40kms-1 cloud behind Sgr A West, are consistent with recent evidence which has demonstrated that Sgr A West lies in front of Sgr A East. The HI optical depth maps of the circum-nuclear disk plus a new HI feature associated with the northern extension of Sgr A West will be presented.