RACS-low3 DR1 raw data

RACS-low3 DR1 raw products

The first data release (DR1) of RACS-low3 consists of 1493 unique tile observations in the lowest band (RACS-low). Note that RACS-low3 differ from RACS-low1 in that it uses a more compact footprint (closepack36 as opposed to square_6x6 used in RACS-low1) to make it coincide with RACS-mid and RACS-high observations and also uses a slightly higher frequency where ASKAP sensitivity is improved (943.5 MHz as opposed to 877.5 MHz used in RACS-low1. All of the raw observed and processed data products for RACS-low3 DR1 (calibrated visibilities, images, and source lists) are made available via the CSIRO ASKAP Science Data Archive (CASDA) by querying for specific scheduling blocks (see list below). 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 from an earlier epoch in the low band, see RACS-low1 DR1. Value-added data for RACS-low3 will be released in future to provide a combined all-sky map and catalogue as was done with RACS-low1.

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-low3 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. Dividing this image by the associated “taylor.0” image effectively gives the spectral index map.
• 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-low3 fields

The following table summarises the RACS-low3 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.