The Rapid ASKAP Continuum Survey III: Spectra and Polarisation In Cutouts of Extragalactic Sources (SPICE-RACS) first data release
Date Issued
2023
Author(s)
Thomson, Alec J. M.
•
McConnell, David
•
Lenc, Emil
•
Galvin, Timothy J.
•
Rudnick, Lawrence
•
Heald, George
•
Hale, Catherine L.
•
Duchesne, Stefan W.
•
Anderson, Craig S.
•
•
Federrath, Christoph
•
Gaensler, B. M.
•
Harvey-Smith, Lisa
•
Haverkorn, Marijke
•
Hotan, Aidan W.
•
Ki Ma, Yik
•
Murphy, Tara
•
McClure-Griffiths, N. M.
•
Moss, Vanessa A.
•
O’Sullivan, Shane P.
•
Raja, Wasim
•
Seta, Amit
•
Van Eck, Cameron L.
•
West, Jennifer L.
•
Whiting, Matthew T.
•
Wieringa, Mark H.
Abstract
The Australian SKA Pathfinder (ASKAP) radio telescope has carried out a survey of the entire Southern Sky at 887.5 MHz. The wide area, high angular resolution, and broad bandwidth provided by the low-band Rapid ASKAP Continuum Survey (RACS-low) allow the production of a next-generation rotation measure (RM) grid across the entire Southern Sky. Here we introduce this project as Spectral and Polarisation in Cutouts of Extragalactic sources from RACS (SPICE-RACS). In our first data release, we image 30 RACS-low fields in Stokes I, Q, U at 25" angular resolution, across 744-1032 MHz with 1 MHz spectral resolution. Using a bespoke, highly parallelised, software pipeline we are able to rapidly process wide-area spectro-polarimetric ASKAP observations. Notably, we use `postage stamp' cutouts to assess the polarisation properties of 105912 radio components detected in total intensity. We find that our Stokes Q and U images have an rms noise of ∼ 80 μJy PSF-1, and our correction for instrumental polarisation leakage allows us to characterise components with ≳ 1% polarisation fraction over most of the field of view. We produce a broadband polarised radio component catalogue that contains 5818 RM measurements over an area of ∼ 1300 deg2 with an average error in RM of 1.6+1.1-1.0 rad m-2, and an average linear polarisation fraction 3.4+3.0-1.6%. We determine this subset of components using the conditions that the polarised signal-to-noise ratio is > 8, the polarisation fraction is above our estimated polarised leakage, and the Stokes I spectrum has a reliable model. Our catalogue provides an areal density of 4±2 RMs deg-2; an increase of ∼ 4 times over the previous state-of-the-art (Taylor, Stil, Sunstrum 2009, ApJ, 702, 1230). Meaning that, having used just 3% of the RACS-low sky area, we have produced the 3rd largest RM catalogue to date. This catalogue has broad applications for studying astrophysical magnetic fields; notably revealing remarkable structure in the Galactic RM sky. We will explore this Galactic structure in a follow-up paper. We will also apply the techniques described here to produce an all-Southern-sky RM catalogue from RACS observations. Finally, we make our catalogue, spectra, images, and processing pipeline publicly available.
Volume
40
Issn Identifier
1448-6083
Ads BibCode
2023PASA...40...40T
Rights
open.access
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