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The Australian SKA Pathfinder (ASKAP) has surveyed the sky at multiple
frequencies as part of the Rapid ASKAP Continuum Survey (RACS).
The RACS-mid survey was published by Duchesne et al. earlier this
year, and
a follow-up paper describes the first set of catalogues from
RACS-mid, covering the sky below a declination of +49 degrees. The
image above is of M51, a source in the highest declination strip of
the survey, with observations centred at a declination of +46 degrees.
Messier 51 is a majestic "grand-design" spiral galaxy, also known as
the Whirlpool galaxy. M51 shows the effects of a close encounter with
NGC 5195, the small galaxy at the outermost tip of one of the arms
toward the top of these images. The images are the RACS-Mid image
(left), VLA NVSS image (centre-left), VLA FIRST (centre-right), and
Digitized Sky Survey (DSS2) optical image. The NVSS (NRAO VLA Sky
Survey) observation was carried out in the VLA's D-configuration, with
a minimum baseline of 35m and a maximum baseline of 1 km, whereas
FIRST (Faint Images of the Radio Sky at Twenty centimetres) was
conducted in the VLA's B-configuration, with a minimum baseline of
210m and a maxiumum baseline of 11 km. In contrast, ASKAP has a
minimum physical baseline of 22m and a longest baseline of 6.4
km. Shorter baselines are more sensitive to extended source structure,
which is why ASKAP and NVSS detect the full extent of the galaxy but
FIRST does not. ASKAP's longer baselines than NVSS result in a higher
angular resolution, which is why it can image the galaxy in finer
detail. All RACS data products are available through the CSIRO ASKAP
Science Data Archive.
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