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An important part of the Rapid ASKAP Continuum Survey (RACS) paper
contained the quality assessments for the first epoch RACS
observations, with considerations of the image noise and sensitivity,
astrometric precision and accuracy, and the flux-density scale. For
each of the 903 image tiles a noise map was generated by dividing the
image into cells of 100×100 pixels and in each, measuring the signal
spread about the mode, allowing an estimation of the root-mean-squared
(rms) noise without contamination by compact sources in the image.
The figure above shows the image noise across RACS survey area,
plotted in Right Ascension and Declination. The Galactic plane, which
lies between the daashed lines, is visible over part of the longitude
range. Two prominent areas have high noise, (i) near an RA of -170
degrees and Dec of 12 degrees, and (ii) near an RA of -60 degrees and
Dec of 40 degrees. These tiles contain the sources Virgo A and Cygnus
A, respectively, which are very bright and have complex structure.
Overall, the median rms noise is 250 µJy/beam, with 90% of RACS images
having a median RMS noise of < 330 µJy/beam. More details are given
in the paper by McConnell et al. published in Publications of
the Astronomical Society of Australia.
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