An HI Search for the Host Galaxies of 27 Radio-loud AGN at z ∼ 2.3

This project was inspired by optical and IR imaging suggesting that, while most QSO hosts at high z are too faint to detect, radio-loud quasars are hosted by exceptionally luminous galaxies. Thus, a search was undertaken for HI absorption against the continuum emission of strong radio emitters whose redshifts (z ∼ 2.3) bring their HI line into the 430-MHz Arecibo passband2. The aim was to detect, or set useful limits, on the HI in the hosts, say in dust lanes, introduced by mergers, or situated in obscuring circumnuclear tori. At Arecibo there is a choice of, a) the 430-MHz line-feed system, or b) the new 430-MHz Gregorian-dome feed. In practice, most of the data were taken with the Gregorian system, although some line-feed data were also acquired. This represents the first Arecibo line spectroscopy using the 430-MHz Gregorian receiver.