HI Surveys with FAST and ASKAP

Surveys of galaxies in the 21-cm line of neutral hydrogen are important parts of the science case for the Five-hundred-metre Aperture Spherical Telescope (FAST) and the Australian SKA Pathfinder (ASKAP). The FAST strawman design with 19 beams and low system temperature allows a “survey speed” comparable to that of ASKAP. The combination of the two telescopes will allow a shallow all-sky survey of over 10 galaxies south of about declination 56. However, the weight limit for the strawman FAST receiver imposes a low-frequency cutoff of about 1.23 GHz (as for the Parkes multibeam design), corresponding to a redshift of 0.16 above which multibeam observations are not possible. To better facilitate deep observations with FAST, and better complement ASKAP surveys, I explore an alternate scenario of a 7 beam FAST design capable of both shallow and deep HI surveys over a wider frequency range.