RACS-low2 DR1 raw data

RACS-low2 DR1 raw products

The first data release (DR1) of the second epoch of RACS low-band data consists of 947 unique tile observations (and an additional 132 fields which were observed twice). All of the raw observed and processed data products for RACS-low2 DR1 (calibrated visibilities, images, and source lists) are made available via the CSIRO ASKAP Science Data Archive (CASDA). NOTE: We do not recommend use of these data products for general science except by expert users, instead we refer the general science user to the curated and combined data products which will be released later.

A limitation of the raw data products is that each observed tile image exhibits reduced sensitivity (increased noise) towards the edge of the field as a result of primary beam attenuation. Furthermore, there may be multiple observations for a given tile in situations where earlier observations had poor sensitivity, poor resolution (as a result of antenna flagging) or high levels of artefacts – so care must be taken when using the raw data products. However, we provide access to this data for transparency and also for specialist science-case use e.g. they provide higher resolution for any individual tile (as they are not convolved to a common resolution with respect to neighbouring tiles), they allow searching for source variability in tile overlap regions and/or in re-observations, they allow for re-processing of visibilities and/or combining visibilities/images from multiple tile observations.

RACS-low2 field images

In this first release, each field will have a number of images associated with it. These are described in more detail here:

• Images with the prefix “image.i” and suffix “taylor.0.restored.conv.fits” are the mean total intensity maps (Stokes I). These have had all synthesised beams restored to a common resolution across the tile and have been corrected to account for the individual primary beam shapes in the mosaic. These are typically the images that would be used for science.
• Images with the suffix “taylor.0.fits” are the mean total intensity deconvolution model images.
• Images may have an associated “taylor.1” image, this is similar to the mean total intensity map but provides additional spectral information. Due to the lack of holography, these images should not be used as they have not been fully corrected for the true primary beam.
• Images with the prefix “image.v” are the circular polarisation maps (Stokes V).
• Images with the prefix “weights” are weights images for the field. These can be used to accurately mosaic neighbouring fields together by taking into consideration the relative sensitivity available at each pixel in the image.

RACS-low2 fields

The following table summarises the RACS-low2 fields. The PSF dimensions are given in arcseconds and the position angle in degrees. The rms column gives the median image rms over the tile in microJanskys.