HIPASS

HIPASS

The HI Parkes All Sky Survey was a blind 21-centimetre neutral hydrogen survey conducted with the Parkes 64-metre radio telescope equipped with a 13-beam receiver. It mapped the southern sky and low northern declinations, producing an extensive spectral-line dataset that enabled source catalogues, follow-up observations, and cross-comparisons with optical and infrared databases. The survey influenced studies connected to galaxy formation, large-scale structure, and the census of gas-rich objects associated with systems such as the Local Group, the Fornax Cluster, and the Magellanic Clouds.

Overview

HIPASS operated from the Parkes Observatory under the Australia Telescope National Facility and CSIRO, targeting the 21-cm line of neutral hydrogen across declinations south of +25°. The programme used drift-scan observing strategies to build spectral cubes covering velocity ranges relevant to Local Group dynamics, the Sculptor Group, and the Hydra–Centaurus Supercluster. The survey area overlapped with regions covered by the Two Micron All Sky Survey, the Sloan Digital Sky Survey footprint southward extensions, and the Infrared Astronomical Satellite catalogues, enabling multiwavelength identification with objects like the Large Magellanic Cloud, the Small Magellanic Cloud, and the Fornax Cluster galaxies. HIPASS connected observational efforts at facilities including the Very Large Array, the Australia Telescope Compact Array, and the Anglo-Australian Telescope for confirmation and higher-resolution imaging.

Survey Design and Instrumentation

HIPASS employed the Parkes 64-metre radio telescope fitted with a 13-beam multibeam receiver developed for programmes linked to pulsar and continuum work at institutions such as CSIRO and the University of Sydney. The multibeam system provided simultaneous beams across the focal plane, increasing survey speed and enabling Nyquist-sampled maps of emission associated with systems like the Magellanic Stream and the Sculptor Group. Spectrometers provided bandwidth and channelisation suited to detect velocity widths from dwarf irregulars to massive spirals such as members of the Fornax Cluster and Centaurus A. Observations were scheduled to optimise coverage and calibration against standards used at Parkes and coordinated with calibration sources observed by teams from the Anglo-Australian Observatory and the European Southern Observatory for flux and bandpass stability.

Data Processing and Catalogue Products

Data reduction pipelines were developed at the Australia Telescope National Facility and partner universities to remove radio-frequency interference, baseline ripples, and scanning artefacts; teams cross-validated methods with datasets from the Very Large Array and the Westerbork Synthesis Radio Telescope. Processed spectral cubes were searched with automated source-finding algorithms and by visual inspection to produce the HIPASS Bright Galaxy Catalogue and the full HIPASS Catalogue, listing positions, velocities, linewidths, and integrated fluxes for thousands of extragalactic HI sources. Catalogues were cross-matched with objects in the Two Micron All Sky Survey, the ESO Nearby Abell Cluster Survey, and the SuperCOSMOS Sky Survey to assign optical counterparts where available, and with H I synthesis maps from the Australia Telescope Compact Array for morphological context. Ancillary products included data cubes, moment maps, and parametrised spectra that supported follow-up proposals at the Hubble Space Telescope and the Gemini Observatory for distance indicators and stellar population studies.

Scientific Results and Discoveries

HIPASS produced a broad array of scientific outcomes: it refined measurements of the HI mass function in the local Universe, constrained gas fractions in dwarf irregulars and low-surface-brightness galaxies such as members discovered in regions surveyed by the Anglo-Australian Telescope, and revealed isolated HI clouds and tidal features associated with interactions involving the Large Magellanic Cloud, the Small Magellanic Cloud, and the Sculptor Group. The survey identified nearby gas-rich galaxies lacking prominent optical counterparts, prompting comparisons with catalogues from the Sloan Digital Sky Survey, the Two Micron All Sky Survey, and targeted spectroscopy at the European Southern Observatory. HIPASS results informed studies of galaxy environment effects in structures like the Fornax Cluster and the Hydra–Centaurus Supercluster, and provided velocity fields used in peculiar velocity analyses connected to the Great Attractor and the Shapley Supercluster. Follow-up high-resolution imaging at the Australia Telescope Compact Array and the Very Large Array resolved HI kinematics in systems analogous to Centaurus A and nearby low-mass systems, calibrating relations involving rotational velocity and baryonic mass relevant to investigations tied to the Hubble Space Telescope distance ladder.

Legacy, Impact, and Follow-up Surveys

The survey legacy includes comprehensive catalogues that seeded subsequent programmes such as the Arecibo Legacy Fast ALFA survey, the ASKAP WALLABY project, and precursor surveys for the Square Kilometre Array, influencing survey design at facilities including the Australian SKA Pathfinder and MeerKAT. HIPASS catalysed multiwavelength follow-up campaigns with instruments like the Hubble Space Telescope, the Very Large Telescope, and the Anglo-Australian Telescope to study stellar content and dynamical masses, and fostered comparisons with cosmological simulations developed by groups at institutions such as the Max Planck Institute for Astrophysics and the Kavli Institute for Particle Astrophysics and Cosmology. Its datasets continue to support research on baryon cycles in galaxies, the distribution of neutral gas in the nearby Universe, and the identification of targets for high-resolution mapping at the Australia Telescope Compact Array and the Karl G. Jansky Very Large Array.

Category:Radio astronomy surveys Category:Parkes Observatory