First ASKAP antenna on-site in Western Australia.

© Galaxies in the Local Volume
(Image credit: B. Koribalski)

WALLABY proposal - accepted (September 4, 2009)

The WALLABY proposal was submitted on the 15th of June, 2009. Thank you to all team members (and particularly the coordinators) for their input. The team currently consists of 85 members from 46 institutions. If you are keen to join and contribute, please email me (Baerbel.Koribalski at

WALLABY: Widefield ASKAP L-band Legacy All-sky Blind surveY

Principal Investigators: Baerbel S. Koribalski (ATNF) and Lister Staveley-Smith (UWA)

Co Investigators: Alexandra Abate (LAL), David Barnes (Swinburne), Carlton Baugh (Durham), Kenji Bekki (UNSW), Nadya Ben Bekhti (AIfA), Chris Blake (Swinburne), Sarah Blyth (UCT), Antoine Bouchard (UCT), Robert Braun (ATNF), Michael Brown (Monash), Pieter Buyle (Ghent), Matthew Colless (AAO), Erwin de Blok (UCT), John Dickey (Tasmania), Simon Driver (St. Andrews), Alan Duffy (UWA), Loretta Dunne (Nottingham), Steve Eales (Cardiff), Alastair Edge (Durham), Bjorn Emonts (ATNF), Jayanne English (Manitoba), Bryan Gaensler (USyd), Karl Glazebrook (Swinburne), Neeraj Gupta (ATNF), Chris Harris (UWA), Martin Hendry (Glasgow), Trish Henning (UNM), Benne Holwerda (UCT), Andrew Hopkins (AAO), Tom Jarrett (IPAC), Matt Jarvis (Hertfordshire), Helmut Jerjen (ANU), Heath Jones (AAO), Gyula Jozsa (ASTRON), Eva Juette (Bochum), Peter Kalberla (AIfA), Juergen Kerp (AIfA), Virginia Kilborn (Swinburne), Sungeun Kim (Sejong), Renee Kraan-Korteweg (UCT), Henry Lee (Gemini), Lerothodi Leeuw (NASA Ames Research Center; SKA South Africa), Angel Lopez-Sanchez (ATNF), Gerhardt Meurer (John Hopkins), Martin Meyer (UWA), Raffaella Morganti (ASTRON), Jeremy Mould (Melbourne), Erik Muller (Nagoya), Tara Murphy (USyd), Hiroyuki Nakanishi (Kagoshima), Ray Norris (ATNF), Seheon Oh (ANU), Tom Oosterloo (ASTRON), Attila Popping (Groningen), Chris Power (Leicester), Peter Quinn (UWA), Somak Raychaudhury (B-ham), Steve Rawlings (Oxford), George Rhee (Nevada), Emma Ryan-Weber (Cambridge), Stuart Ryder (AAO), Elaine Sadler (USyd), D.J. Saikia (NCRA), Paolo Serra (ASTRON), Kristina Spekkens (RMC), Anja Schroeder (KAT Office), Christian Struve (ASTRON), Mark Thompson (Hertfordshire), van der Hulst (Kapteyn), Wim van Driel (Paris), Marc Verheijen (Kapteyn), Bart Wakker (Wisconsin), Brad Warren (UWA), Rachel Webster (Melbourne), Tobias Westmeier (ATNF), Matthew Whiting (ATNF), Eric Wilcots (Wisconsin), Richard Wilman (Melbourne), Benjamin Winkel (AIfA), Ivy Wong (Yale), Min Yun (UMass), Daniel Zucker (AAO/Macquarie), and Martin Zwaan (ESO).


We propose an extragalactic neutral hydrogen (HI) survey which will cover 75% of the sky (-90 degr < DEC < +30 degr), producing the largest sample of galaxies that is possible to observe in a given observing time with ASKAP. The fundamental aims of this proposal are to examine the HI properties and large-scale distribution of ~500,000 galaxies out to a redshift of 0.26 (equivalent to a look-back time of ~3 Gyr) in order to study: (1) galaxy formation and the missing satellite problem in the Local Group, (2) evolution and star-formation in galaxies, (3) mergers and interactions in galaxies, (3) the HI mass function and its variation with galaxy density, (4) physical processes governing the distribution and evolution of cool gas at low redshift, (5) cosmological parameters relating to gas-rich galaxies, and (6) the nature of the cosmic web. WALLABY will provide the largest, most homogeneous HI sample of galaxies, complemented by similarly uniform multi-wavelength data, and will be an important pathfinder for key SKA HI science projects.

To achieve the above, we propose to observe each 30 deg2 ASKAP field for a single period of 8 hours in the frequency range 1.13 to 1.43 GHz (corresponding to -2000 < cz < 77,000 km/s) and divided into 16,384 spectral channels (ie. 4 km/s rest-frame velocity resolution). The total integration time, slightly dependent on tiling algorithm, will be around 13 months. The WALLABY survey parameters are well-aligned with the other all-sky survey SSPs, e.g. EMU (radio continuum), POSSUM (polarization), FLASH (absorption), and will facilitate other science such as fast and slow transient detection. An important part of the WALLABY science includes continuum emission from gas-rich galaxies (providing a measure of their star-formation rate), Damped Lyman alpha absorption analogs (a measure of disk cross-section and gas temperature), and the use of gas dynamics to assist in the interpretation of the magnetic field properties of the nearby extended galaxy population. Discussions with other SSP proposers and pipeline developers are under way.

WALLABY will have a flux sensitivity some 20 times better than the HI Parkes All-Sky Survey (HIPASS), at a velocity resolution some 4 times better, and will detect 20 times more galaxies than the ongoing Arecibo ALFALFA survey with six times better spatial resolution. WALLABY will detect dwarf galaxies (MHI = 108 M*) out to a distance of ~60 Mpc, massive galaxies (M*HI = 6 x 109 M*) to ~500 Mpc, and super-massive galaxies like Malin 1 (MHI = 5 x 1010 M*) to the survey `edge' of 1 Gpc. The mean sample redshift is expected to be z = 0.05 (200 Mpc). While the majority of the detected HI galaxies will be spatially unresolved with the ASKAP 2-km configuration, we expect all to be spectrally resolved. For the ~1000 galaxies which will be spatially well-resolved (>5' or >10 beams across), we will obtain data similar in quality, sensitivity and resolution to the ~300 nearby galaxies recently imaged in major interferometer studies, including the `Local Volume HI Survey' (LVHIS) at the AT Compact Array, THINGS, Little THINGS and ANGST at the VLA, FIGGS at the GMRT, and WHISP at the WSRT (see summaries in Koribalski & Jerjen 2008). For the ~3 x 104 galaxies expected to be larger than 1.5', we will be able to measure simple structural, mass and angular momentum parameters. For this purpose, we plan an automated parametrization pipeline.

For each detected galaxy WALLABY will deliver the following data products: (1) a 3D data cubelet, (2) an integrated HI spectrum, (3) an HI column density image, (4) a radio continuum image, and (5) a full parametrization of galaxy properties, as well as - for extended sources - (6) a velocity field, and (7) a dispersion field. In addition, we plan to search for faint HI emission in well-selected optical/IR galaxy samples by co-adding (`stacking') the HI data at the position and redshift of the optical/IR galaxy. These extra redshifts will come from recent 2MASS-selected galaxy surveys such as 6dFGS and from possible spectroscopic extensions based on deeper optical/IR samples.

WALLABY will deliver data suitable for a range of studies, from High-Velocity Clouds (HVCs) at the edge of our Galaxy, to new Local Group galaxies, from a census of galaxies in the Local Volume, out to distant clusters and super-clusters. The volume covered (0.4 Gpc3 for M*HI galaxies) is large enough for the measurement of cosmological parameters without substantial cosmic variance. We expect to be able to accurately measure the density-dependence of the HI mass function, the clustering and bias parameter for gas-rich galaxies and the local flow field. Further, we expect a possible detection of baryonic acoustic oscillations at the lowest redshift. Independently of forthcoming optical surveys, WALLABY could reduce the errors on the dark energy parameter w and the Hubble Constant h by up to a factor of two when compared with PLANCK-only data. But more importantly (given the rapid progress of dark energy surveys currently underway), WALLABY will serve as an accurate zero-redshift anchor for later SKA HI surveys of the distant Universe and will inform SKA HI survey designers of parameters which are presently poorly known. As with HIPASS, WALLABY is also expected to detect a large number of interacting gas-rich galaxies missing in optical surveys of the Local Universe and, through comparison with new generations of optical (SkyMapper, PanStarrs, VST, LSST), infrared (VISTA, WISE, Herschel) and millimetre/sub-millimetre (ALMA) observations, will deliver a new synoptic view of the Local Universe.