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First absorption line for the SKA precursor ASKAP

4 December 2013, Sydney, Australia –  CSIRO’s ASKAP commissioning team has achieved a new science demonstration with the first HI absorption line measured with ASKAP antennas at the Murchison Radio-astronomy Observatory (MRO) in Western Australia.


This image is a montage of the configuration of the source (an optical image of the gravitationally lensed system from HST), a picture of the Einstein Ring (from MERLIN) and the ASKAP HI absorption spectrum produced by the commissioning team. The prominent HI absorption feature from an intervening galaxy, at z=0.89, can be seen at a frequency of 753.5 MHz.

The result successfully demonstrates that the HI spectral line mode of ASKAP reproduces faithful results in a well-characterised astronomical region, and is an important step towards ASKAP Early Science.

Using three ASKAP antennas installed with ASKAP’s first generation phased array feed (PAF) receiver system and the hardware correlator, a baseline-averaged cross correlation spectrum was produced of the gravitationally-lensed system PKS 1830-211 (the discovery of which was presented in a Nature article in 1991). This system has an absorbing galaxy at a redshift of z=0.89.

A six hour observation of the source was conducted with the three baselines; the data were captured at full spectral resolution using the full bandwidth of the hardware correlator.


For a very simple reduction the amplitude was determined for each visibility and these amplitudes were then averaged across the duration of the observation and over the three baselines.

Full release is available on the CSIRO’s website at: