WALLABY is the "ASKAP HI All-Sky Survey", a precursor for future, much deeper SKA Phase 1 & Phase 2 neutral hydrogen (HI) surveys. With an integration time of ~1 year (or 8 hours per pointing) WALLABY will cover two-thirds of the sky to redshifts of z = 0.25. Using our best source-finding algorithms (Koribalski 2012a), we estimate that in the survey volume around 600 000 galaxies are detectable in the 21-cm line of neutral atomic hydrogen (Duffy et al. 2012; Koribalski & Staveley-Smith 2009; Johnston et al. 2008). We will measure the HI properties of each galaxy and derive its distance, HI mass, total mass and dark matter content. Most galaxies will also be detected in the 20-cm radio continuum, allowing us to derive their star-formation rates. The 30 arcsec angular resolution of WALLABY will allow us to identify likely optical and/or infrared galaxy counterparts. - For a brief overview of WALLABY see Koribalski (2012b).
Apr 2013: First 3-beam image with three ASKAP PAFs
In August 2012 first fringes between three PAF-equipped ASKAP antennas as well as zero closure phase measurements were obtained towards the radio galaxy Virgo A (M87). In April 2013 the first high-quality multibeam image was obtained with the BETA1 system (928 MHz, 16 x 1 MHz bandwidth, 1 pol, 12h integration time, all with the interim software correlator). We look forward to testing and first results from the hardware correlator later this year. This will be followed by science commissioning with the first six PAF-equipped ASKAP antennas - known as BETA.
2012 PASA Special Issue (Vol 29, Issue 3)
The 2012 PASA Special Issue on Source Finding and Visualisation is now complete and all papers are online. I like to thank all authors for their contributions.
2012 SKA Site Decision
On May 25, 2012, the SKA Members met and adopted a dual-site implementation for SKA Phase 1 and SKA Phase 2. The SKA Phase 1 implementation will use existing (or currently being built) infrastructure at both sites, including the precursor telescopes, ASKAP in Australia and MeerKAT in South Africa. After demonstrating the power of PAFs on ASKAP (and WSRT), it is planned - as part of SKA Phase 1 - to add an array of 60 PAF-equipped dishes to ASKAP.
2011 Simulations Fest
- Homepage & Registration
- Workshop Program, Abstracts (incl. pdf files of most presentations), and Participants
- Data Visualisation
ASKAP is the "Australian SKA Pathfinder". See ASKAP Live ! and the ASKAP Webcams for up-to-date information. As ASKAP design and software are progressing rapidly, we have assembled international science teams who will carry out survey design studies, liase with the software team, explore the sky via cosmological simulations and write many excellent papers.
WALLABY - led by B. Koribalski and L. Staveley-Smith - is the top-ranked spectral line survey. It will observe the sky up to declinations of +30 degr over the frequency range of 1130 - 1430 MHz, ie velocity range of -2,000 to +77,000 km/s at approx. 4 km/s resolution. Assuming a Tsys of 50 K we will integrate for 8h (or more) per field. See our survey proposal for details.
ASKAP will consist of 36 x 12-m antennas (4072 sq m) with phased array feeds providing a field-of-view of 5.5 deg x 5.5 deg (= 30 sq deg) operating in the range 0.7 - 1.8 GHz, i.e. ideal for large HI line and 20-cm continuum surveys. The inner 30 antennas (3400 sq m) of ASKAP are optimally arranged in a 2-km configuration, delivering an angular resolution of 30". A further six antennas will be placed at larger distances (baselines up to 6-km), giving an angular resolution of ~10".
The first ASKAP antenna arrived on site in December 2009. The picture at the top shows the fully assembled antenna on its pad in Western Australia (WA). Phased array feed (PAF) design is on-going with testing under way on the Parkes 12-m test antenna. Recent Tsys results of the PAF MkII system are very encouraging (close to Tsys = 50 K across the band). --- Construction of all 36 ASKAP antennas is now complete. PAFs are currently installed on four antennas (1, 3, 6 & 8); two more PAFs are undergoing final system tests before delivery to the site. Engineering commissioning is continuing and will soon be including first spectral line observations.
ASKAP + WSRT-APERTIF
A true all-sky survey cannot be achieved with a single ground-based telescope alone. While ASKAP can "see" more than 2/3 of the sky, it cannot see the whole sky. WSRT equipped with focal plane arrays (APERTIF) would provide the ideal complement to ASKAP. An APERTIF Expression-of-Interest for a WSRT Northern Sky HI Survey (WNSHS; DEC > +27 degr) was submitted on Sep 22, 2010 (led by Gyula Jozsa). A full proposal is now being prepared.
Funding of the Pawsey Centre and the NBN link between Geraldton and Perth may in future (tbd) provide the computing power needed to process the full spectral line visibilities from all 36 ASKAP antennas with baselines up to 6-km, in contrast to the previous limitation to the inner 30 antennas (baselines < 2 km). This has many implications:
- maximum angular resolution increases from about 30" to 10"
- pixel size has to decrease from 10" to around 3" (i.e., cubes will be 10x larger !)
- increased number of baselines (from 435 to 630)
- increased point source sensitivity (factor ?)
- expanded, but less uniform uv-coverage as compared to that of the inner 30 ASKAP antennas (see image below) => higher sidelobes levels
- high-resolution "postage stamps" will be obsolete
Questions to address:
- the optimum weighting of the ASKAP visibilities needs to be evaluated and tested using simulations (and later BETA)
- re-consider WALLABY products: initially we requested one data cube per pointing at 30" resolution, now we may require two or more data cubes per pointing at different angular resolutions (=> to be investigated)
- what angular resolution is required to match with a future
WSRT+APERTIF HI survey of the northern sky
Caption: ASKAP uv-coverage with 30 (red) and 36 (blue) antennas, created with the V.R.I. tool.
Idea: develop GalaxyZoo for Wallaby :)
Page design and maintenance: B. Koribalski
Last updated on the 17th of April, 2013