ASKAP Commissioning News
The construction of ASKAP is nearing completion with 24 antennas having been handed over for commissioning and integration into the array. The remaining antennas await installation of their digital processing systems, scheduled to occur mid-2018. Delivery of ASKAP’s capabilities to the astronomical community will happen in staged “array releases” of increasing scope.
The next major milestone will be array release 3, which consists of 18 antennas, 288 MHz of bandwidth and for the first time, the ability to exchange bandwidth for frequency resolution (known as “zoom modes” within the community). Array release 3 will also offer the longest baselines (and therefore highest image resolution) to astronomers for the first time. Zoom modes will enable studies of neutral Hydrogen and other spectral lines within the Milky Way, providing a more detailed picture of gas dynamics and stellar feedback.
Array release 4 is the full ASKAP system with 36 antennas and this is currently scheduled for release on a shared-risk basis in early 2019.
One of the major challenges faced by ASKAP is the desire to begin survey operations early in the life cycle of the telescope. Most radio telescopes spend the first few years of operation conducting smaller-scale projects while the system reaches the level of maturity required to conduct large-scale all-sky surveys (which represent a major investment in time).
ASKAP will be expected to perform large-scale surveys very early in its operational lifespan, requiring particular attention to detail during commissioning. To gain experience with survey operations, we intend to conduct a series of “pilot surveys”, which will be designed to investigate specific targets that provide a good test of the telescope’s characteristics (sensitivity, dynamic range, calibration stability, etc.).
At a recent meeting of ASKAP’s science team principal investigators we described the planned array release schedule including readiness to take 36-antenna survey data in some form in early 2019. There was also discussion of plans to review the original survey proposals. Given the time that has passed since the original call for proposals there was consensus that a reassessment of the survey scientific goals and technical feasibility is required at some point in the near future, though the timing of this process is still under consideration.
The scientific climate has changed significantly (particularly in the field of transient detection) during this time. As we move towards array release 4, it will be important to maintain close ties with the science teams and we expect to host more of these discussions every few months. This will allow us to prioritise development of key systems (such as the science data pipeline software) based on up-to-date science requirements.
Evolutionary Map of the Universe (EMU) Survey News
EMU early science has started, with observations of several fields including the SCORPIO field in the Galactic Plane, and the Small Magellanic Clouds. The analysis of both fields has already demonstrated ASKAP’s potential for discovering new supernova remnants, HII regions and planetary nebulae in the Galaxy and the early science teams at INAF Catania Observatory, Italy and Western Sydney University, have already started writing up journal papers to report several new discoveries (Umana et al., in prep.).
Work has also started on the 2000-square degree “Early Science Cosmology Field”, which will be used to test the EMU Cosmology Pipeline developed by David Parkinson of KASI, Korea, and his colleagues, and perhaps deliver some significant independent constraints on the fundamental cosmological parameters.
We are particularly excited to measure an rms noise level in the ASKAP-12 images of about 60uJy/bm, which translates to an rms in the final EMU survey of about 15 uJy/bm, although our calibration and weighting are not yet optimum so the final figure is still somewhat uncertain.
The ASKAP HI All-Sky Survey (WALLABY) Survey News
The WALLABY science team has collected just over 700 hrs of commissioning and Early Science observations on four different fields: the NGC 7232 and Dorado groups, Fornax cluster, and a field around the M83 spiral galaxy. The 220 TB of raw data will produce high resolution neutral hydrogen image cubes with full WALLABY sensitivity (i.e. have an RMS noise of 1.6 mJy/beam per 4 km/s channel). These cubes will provide detailed maps of the hydrogen gas content of nearby systems and enable the discovery of new galaxies. The next step for WALLABY will be verifying the ASKAP data products and analysing them for scientific purposes. Feedback from this process will help in planning the next generation of pilot surveys as we begin ramping up to full operations.