Welcome
WALLABY is the "ASKAP HI All-Sky Survey", a precursor for future, much deeper SKA HI surveys. With an integration time of about 1 year (or 8h per pointing) WALLABY will cover two-thirds of the sky to redshifts of z = 0.25. Using our best source-finding algorithms, we estimate that in the survey volume around 500 000 galaxies are detectable in the 21-cm line of neutral atomic hydrogen. 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-forming rates. The 30 arcsec angular resolution of WALLABY will allow us to easily identify likely optical and/or infrared counterparts.
In December 2011 we briefly had the first three Phased Array Feeds (PAFs) on antennas 1, 3, and 6. First fringes were obtained between the PAF on antenna 3 and a single feed on antenna 8. - Go ASKAP !
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2011 Physics Nobel Prize
Congratulations to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae". - Awesome.
2011 Simulations Fest
- Homepage & Registration (Rego is Aus$100 incl the Harbour Cruise)
- Workshop Program and Abstracts (incl. pdf files of most presentations)
- Participants
- Data Visualisation
General Information
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 is the top-ranked spectral line survey.
WALLABY parameters: sky coverage = -90 < DEC < +30 degr; freq. coverage = 1130-1430 MHz, ie vel = -2,000 to +77,000 km/s at 4 km/s resolution; approx. 8h (or more) integration time per pointing. 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 (FOV) 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 < 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. All ASKAP antennas are now on-site in various states of construction: 19 antennas are complete with reflectors and 15 antenna pedestals are ready. The first PAF was installed on Antenna 3 in October 2011. The second and third PAF are soon to be re-installed, ready for testing in mid 2012. Another three PAFs are being assembled in the Marsfield labs. BETA, i.e. six ASKAP antennas with PAFs, will hopefully be ready for testing by the end of 2012.
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). With a 4h on-source integration time this survey would provide similar resolution and sensitivity to WALLABY (assuming we integrate 8h with ASKAP); we are also considering 12h integration times to accommodate telescope and other survey requirements. A full proposal is now being prepared.
Recent developments
Recent 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.
IDEAS !
Idea: develop GalaxyZoo for Wallaby :)
Page design and maintenance: B. Koribalski
Last updated on the 3rd of May, 2012