Detection of an H I disk in Hydra A?

Abstract

We present new observations of the H I absorption system seen toward the core of the radio galaxy Hydra A, which is the central galaxy in a cooling flow cluster Abell 780. Our improved spatial (approximately 2 sec) and velocity (approximately 1.4 km/s) resolutions indicate that the absorption arises very close to the nucleus, probably in a gas disk located in the central regions of the galaxy. There is no indication that any of the absorption arises in the cooling flow. The H I absorption is seen only toward the core and is within approximately 100 km/s of the systemic velocity. The absorption covers a velocity range approximately 100 km/s. It can be decomposed into six Gaussian components with widths approximately 10-20 km/s and optical depths approximately 0.1-0.5. No narrow line features (approximately 1 km/s) were detected in Hydra A to a 3 sigma optical depth limit of 0.06.