VLA synthesis of galactic H I absorption toward 3C 123

Abstract

The VLA was used to synthesize a map of galactic 21 cm absorption across the nearly 20 arcsec extent of 3C 123 with 2.8 arcsec resolution. Three prominent absorption lines can be traced. All three show angular structure, although only the high-velocity line shows 100% variation in equivalent width. The other two lines - one a molecular cloud, the other an intermediate-velocity diffuse cloud - show much weaker structure since variations of only a few percent in equivalent width are seen. In spite of this structure, the average results are in good agreement with earlier single-dish data. Crude statistical analysis suggests that the strong variations of the high-velocity cloud are resolved by the 2.8 arcsec beam, whereas the weak fluctuations in the molecular cloud are unresolved.