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 (PASA Special Issue 2012 - ed. Koribalski), we estimate that in the survey volume around 600 000 galaxies are individually detectable in the 21-cm line of neutral atomic hydrogen (Johnston et al. 2008; Koribalski & Staveley-Smith 2009; Duffy et al. 2012). 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).
May 2014 NEWS * ASKAP detects NGC 253's extended HI disk
In May 2014 the first extragalactic ASKAP HI observations were attempted with six Mk1 PAFs (ie 15 baselines, 2 pols). In just two hours the target galaxy, NGC 253, was detected in HI emission on the shortest baselines and in HI absorption on the longest baselines. This was followed by a 12 hour ASKAP observation, which revealed the HI disk of NGC 253 - as known from extensive ATCA HI observations. - The ASKAP HI data calibration and imaging is led by Paolo Serra. - We chose NGC 253, located in the nearby Sculptor Group and seen edge-on, because it is an extremely bright and well-known starburst galaxy. Its hydrogen disk spans about 0.5 degr on the sky, resulting in a distinctive HI double-horn profile. NGC 253's radio core is extremely bright, most helpful for the ASKAP data calibration and imaging at this early stage. We will very soon move on to map other nearby galaxies in HI. Watch this space !
Apr 2014 * First ASKAP 15 baseline observations
The first observations with the 15 baseline BETA array (ie, six PAF-equipped ASKAP antennas) are rolling in. See the recent image of PKS 1830-211 and high resolution (18.5 kHz) spectra of the associated HI absorption lines.
Feb 2014 NEWS * WALLABY Newsletter No 5
- Our latest newsletter (WALLABY Newsletter No 5) is ready. Thank you very much to all the contributors !! And to all readers - enjoy :)
PhD top-up scholarship
- I can now offer a second PhD top-up scholarship for a co-supervised HI project (Job Ref - NSW14/00135; closing date: 31 May 2014; contact B. Koribalski) - Further information. - The first PhD top-up scholarship was awarded to Katharina Lutz at Swinburne University, supervised by Virginia Kilborn and me.
Feb 2014 NEWS: First 9-beam image with six ASKAP PAFs
In February 2014 the first 9-beam image was made using the full 304 MHz bandwidth and combining the data from two BETA sub-arrays, each consisting of three PAF-equipped ASKAP antennas. The three bright extragalactic sources in the field are PKS 1610-771, PKS 1549-790 and PKS 1547-795. The associated press release is here.
Oct & Nov 2013: First HI detection with three ASKAP PAFs
On Oct 16, 2013, the first HI detection was made with three ASKAP PAFs. Auto-correlation spectra for a single PAF port were obtained using the hardware correlator; our target was the standard Galactic S9 region located at RA,DEC(J2000) = 17:52:05.4, -34:25:15.4, Bruens et al. 2005).
In Nov 2013 the first HI absorption detection was achieved towards the gravitational lens PKS 1830-211 at z = 0.89 using the cross-correlation data from three BETA antennas. - Further ASKAP HI observations will be carried out soon and will hopefully result in the first ASKAP HI cube.
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). The first 9-beam image was recently obtained using three PAFs and the new hardware correlator. Another three Mk1 PAFs are currently being installed on site. Engineering and science commissioning with six PAF-equipped ASKAP antennas - known as BETA - is expected to happen towards the end of 2013.
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 all six BETA antennas (1, 3, 6, 8, 9 and 15). 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 1st of June, 2014