HI Parkes All Sky Survey

The ‘HI Parkes All Sky Survey’ (HIPASS) covers the whole southern sky as well as northern declinations up to +25 degrees. HIPASS commenced in Feb 1997, and the last northern scans were taken in 2002. HIPASS was carried out with Murriyang, the Parkes 64-m radio telescope equipped with a novel 21-cm multibeam system. The latter comprised a cooled, 13 beam receiver and digital correlator (Staveley-Smith et al. 1996). The 64 MHz observing band, centred on 1394.5 MHz, was divided into 1024 channels, providing a velocity range of -1280 < cz < 12700 km/s with a channel width of approx. 13.2 km/s and a velocity resolution of 18 km/s. The HIPASS integration time per beam is 450s. After gridding an r.m.s. noise of about 13.3 mJy was achieved in the first set of HIPASS cubes. The observations and techniques used to calibrate and image the data are described in Barnes et al. (2001). The processing algorithms are successfully designed to be statistically robust to the presence of interference signals and are particular to imaging point (or nearly point) sources, not extended emission. Specifically, a major improvement in image quality was obtained by designing a median-gridding algorithm which used the median estimator in place of the mean estimator. While the average Parkes beam FWHM is 14.3 arcmin, the average gridded HIPASS beam was about 15.5 arcmin.