Radio Telescopes as Spectrometers; the challenges of Square kilometre Array Pathfinders

Dr. Chenoa Tremblay(CSIRO, Australia)

May 17, 2021

There are several SKA white papers covering non-HI spectral line studies below 2GHz. The science cases for these span across Interstellar Medium physics and composition, star formation, active nuclei, and cosmological applications. The research includes searching for particular atomic and molecular transitions that can be detected by existing precursors instrument at the Murchison Radio-Observatory: ASKAP and MWA. There are also new science goals that could use these instruments, that were not realised in the 2015 white papers, including the search for Axion dark matter particles. Both the Murchison Widefield Array (MWA) and the Australian SKA Pathfinder (ASKAP) are currently performing spectral line surveys as precursor instruments. Spectral line data processing with both facilities requires a significant amount of computing resources to complete, for example three hours from a single night with the MWA to study spectral lines generates 87,264 final images of the sky and requires 52,000 CPU hours to process (assuming no problems or failures occur). This example does not include the time to download and calibrate the data done by the All Sky Virtual Observatory service. The MWA spectral line surveys require imaging the sky in snapshots and integrating the data together in software, as it cannot track the source. However, the processing feat is not any less substantial with ASKAP, where source tracking is possible. A single ~10 hour spectral line observation with 0.2kHz resolution takes over 70 TB of disk space to calibrate and >150,000 CPU hours to process at the Pawsey Supercomputing Centre. This represents what we have feasibly been able to process so far (approximate 1/15th of the amount of data collected) and does not yet reach the potential of the full science goals. I would like to discuss these challenges in the context of future SKA regional centres and the ways in which we they may inform data processing as well as the non-HI spectral line science with these two telescopes, how the two instruments could work in tandem to start answering questions about ISM physics and star formation, and the challenges we face in doing so.

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