ASKAP Science Update CSIRO Astronomy and Space Science September 2011 The ASKAP Science Update is a regular series dedicated to conveying the latest news about the Australian SKA Pathfinder (ASKAP) project to the international science community. It is also available online at www.atnf.csiro.au/projects/askap. Preparing for first BETA Johnston together with members of for observation because much is already Observations with ATCA the ASKAP Survey Science Teams. known. Both the Fornax cluster and Circinus have been extensively mapped As part of preparations for BETA According to ASKAP Project Scientist in neutral hydrogen (HI) and 20cm (Boolardy Engineering Test Array), the Ilana Feain, the two fields were chosen, radio continuum, and the radio galaxy ASKAP Project Scientist and members for very specific reasons, in consultation Fornax A has been studied in polarisation of the Survey Science Teams began with the Principal Investigators of the ten and radio continuum both at ATCA characterisation of two 30 deg2 fields ASKAP Survey Science Projects (SSPs). and the Very Large Array (VLA). during two separate week-long ATCA “The fields were purposefully chosen for Despite the level of detail already observing sessions during May and June. content and location – approximately available for certain parts of the two BETA is an array of the first six ASKAP 12 hours apart on the sky – so that fields, the aim of the characterisation was antennas installed with Phased Array no matter what time of day or night to achieve a 30 deg2 field at equivalent Feed (PAF) receivers at the Murchison we are able to use BETA, there will be angular and spectral resolution and Radio-astronomy Observatory (MRO) a fully characterised field available to sensitivity and frequency of BETA. in Western Australia. initiate science verification,” says Ilana. The team was allocated 14 full days of Although primarily an engineering and “When we observe these first science ATCA observing time, and observations scientific commissioning instrument, fields with BETA for the first time, we were run 24 hours a day over two early astronomy observations may want to compare our results with what separate seven-day blocks – 12 be possible with BETA once the we know we should see, in order to test hours each for Fornax and Circinus instrument is fully tested and during data quality and integrity of the system.” – in two array configurations (750b times when it is not otherwise One of the chosen fields is centred close and 1.5b) that together closely required for commissioning activities. to NGC 1365 in the Fornax cluster, the match the uv-coverage of BETA. Characterisation observations took other is centred close to the Circinus The two fields shown here, from the place using CSIRO’s Australia Telescope galaxy. Previous multi-wavelength surveys Sydney University Molonglo Sky Survey Compact Array (ATCA) during May on small regions within each of these (SUMSS), are overlaid with a set of and June, by Ilana Feain and Simon fields make them the perfect candidates coloured circles representing the daily ATCA pointings required to mosaic the full region. BETA will cover each of these regions in its single 30 deg2 field of view. “These images will allow us to test BETA calibration and imaging pipelines, allow for verification and refining of the source finding and cataloguing techniques, in addition to a range of data quality tests,” explains Ilana. “These two fields act as our control fields against the unknown and possibly variable calibration systematics of a new telescope.” > The two fields chosen as ‘first science with BETA’ characterisation fields. The left is centred on the Fornax cluster and contains the bright extended radio galaxy Fornax A (bottom right). The right is centred on the barred spiral Circinus galaxy and contains extended emission from the Milky Way (top right). Both images are shown at 843MHz from the Sydney University Molonglo Sky Survey (SUMSS) overlaid with a set of coloured circles representing the daily ATCA pointings. Credit: Ilana Feain. “The combination of features that makes ASKAP so unique is also what makes FLASH possible.” ASKAP Survey Science Projects In this edition of ASKAP Science Update As Elaine explains, FLASH will break measurements will be made with other we take a detailed look at the final new ground in low redshift investigation, telescopes like the AAT and ALMA. whereas existing radio telescopes have two of the ten Survey Science Projects There is also scope for high levels of reached the limits for HI studies. (SSPs) that will make use of ASKAP collaboration between FLASH and during its first five years of operation. “Blind HI absorption surveys are the other ASKAP SSPs, especially not possible on current-day radio WALLABY and DINGO. “Since our FLASH telescopes due to limitations in spectral current knowledge is so incomplete, Sensitive observations of distant bandwidth, RFI and survey speed. The anything we can learn about gas in distant galaxies have made it possible to map combination of features that makes galaxies will be useful in planning and out the star-formation history of the ASKAP so unique, in particular the wide preparing for the SKA,” says Elaine. field-of-view and spectral bandwidth, Universe in detail, yet almost nothing is “The WALLABY and DINGO surveys is also what makes FLASH possible.” currently known about the distribution will provide us with rich HI data sets of the cold neutral gas from which Rapid sky coverage will be essential for which will certainly provide new insights these distant stars are formed. FLASH. With 150,000 sightlines planned into the gas content of galaxies. Similarly, Radio emission surveys give some (that’s 375 times the number of sightlines the information we expect FLASH will clues to this, by detection of weak to bright continuum sources that have produce may complement these surveys neutral hydrogen (HI) at lower been searched over the last 30 years), by providing our first look at the HI redshift, yet current day radio approximately only 1% are expected to properties of galaxies in the unexplored telescopes are stretched to their limit yield strong HI absorption, so the team redshift range beyond z = 0.5” will need to extract around 150 radio beyond z = 0.1, leaving almost 80% She concludes, “HI absorption-line spectra from each ASKAP field for testing. of cosmic time unexplored in HI. surveys covering large areas of sky have The vast collecting area of the Square Additionally, as FLASH will focus on a never been possible before. What’s most Kilometre Array will open up an entirely lower range of frequencies (700 – 1000 exciting to me is that ASKAP’s unique new vista of the early universe, but MHz), it would be highly susceptible to ability to cover the sky rapidly and some astronomers, such as those terrestrial radio interference. The radio- observe many bright sources at once involved in the First Large Absorption quiet environment of ASKAP’s home will allow us to extend our study of HI in Survey in HI (FLASH), are not content at the Murchison Radio-astronomy galaxies out to a cosmic epoch, around to wait until the SKA is built to probe Observatory (MRO) in Western Australia five to eight billion years ago, which is galactic content at low redshift. is therefore the perfect place for FLASH. completely unexplored until now.“ As Principal Investigator (PI), Elaine Though Elaine describes the project Sadler will lead the FLASH project, as ‘observationally simple’, the main a blind HI absorption-line survey challenge facing the FLASH team will using ASKAP that uses background be data interpretation, and the plan to radio continuum sources to identify reconstruct a whole galaxy from just and characterise foreground neutral the small piece that they will see. hydrogen. Absorption surveys have “We already know the positions of the advantage that detection sensitivity the target sources, since these are in depends only on the brightness of the existing catalogues of the radio sky background radio source, rather than made by earlier surveys,” she explains. the distance to the intervening galaxy. “Unlike an emission-line survey, This will allow the team to study HI in where we would map the whole galaxies at much larger distances than galaxy, absorption-line surveys only emission-line surveys, and provide a give us information on a single small significant dataset to study gas assembly sightline that runs through a galaxy.” and galaxy formation during a time To overcome the challenge, once in history of the Universe which has an absorption line is detected, >Elaine Sadler, Principal Investigator been left largely unstudied thus far. follow-up optical and CO emission of FLASH. Credit: Keith Shortridge. CRAFT The lure of the unknown is a common theme in astronomy, and for the Commensal Real-time ASKAP Fast Transient (CRAFT) survey, it is what drives the team. CRAFT will operate in tandem with other ASKAP SSPs, collecting and processing data in real-time in order >An image from V-FASTR, showing one pulsar pulse identified via an incoherent to search for signals that appear for rocessing path and a machine-learning algorithm, a possible technique that could less than milliseconds at a time. There solve the challenge of data processing with ASKAP. Credit: CRAFT / ICRAR. are a number of possible objects that may be detected (such as giant gravitational fields,” says Peter, “and project (the VLBA fast transient project), pulses, rotating radio transients, detection of extragalactic transients is already underway using the US Very magnetars, even SETI signals), but would give us an entirely new probe Long Baseline Array, which allows the CRAFT is not yet playing favourites. on the huge reservoir of baryons team to investigate the challenge of For Principal Investigator Peter Hall, in the intergalactic medium.” detection methods and data processing.