VLA observations of 21 centimeter H I absorption toward Cassiopeia A

Abstract

A multiconfiguration aperture synthesis mapping of the Perseus arm H I absorption line toward Cas A has been performed using the VLA. The sensitivity achieved was sufficient to detect optical depths as low as 0.03 and as large as about 5 over a region about 5 arcmin in diameter. Optical depth images are presented as gray scale with contours superposed for 41 spectral channels showing H I absorption. Representative optical depth spectra are shown as a function of position over Cas A. The images represent a significant improvement in angular resolution over earlier aperture synthesis work. The H I images show much structure in the absorbing gas, with the morphology dominated by elongated structures. 22 refs.