The Rapid ASKAP Continuum Survey VII: Spectra and Polarisation In Cutouts of Extragalactic Sources (SPICE-RACS) Second Data Release -- Unveiling the Magnetised Sky

TL;DR

The SPICE-RACS DR2 provides an extensive, high-quality catalogue of Faraday rotation measures and spectral data for millions of extragalactic radio sources, significantly advancing the study of cosmic magnetism.

Contribution

This release offers the largest single RM catalogue to date, with detailed spectral cubes and polarisation data covering most of the southern sky, enabling new magnetism research.

Findings

Detected over 250,000 RMs with high significance

Achieved an areal RM density of 6.7 deg^{-2}

Provided publicly accessible, high-resolution spectral and polarisation data

Abstract

We present the second data release (DR2) of Spectra and Polarisation in Cutouts of Extragalactic sources from RACS (SPICE-RACS). SPICE-RACS DR2 is derived from the third low-band epoch of the Rapid ASKAP Continuum Survey (RACS-low3) and covers the entire sky from the South celestial pole up to a declination of $+49^\circ$; approximately 87.5% of the celestial sphere. We produce 'cutout' spectral cubes in Stokes $I$, $Q$, $U$ around 4 million radio sources and extract spectra towards 5 million radio components. Across our observed band of 799.5--1087.5 MHz we find an $rms$ noise of $\sim200\mu\mathrm{Jy/PSF}$, an angular resolution of $\sim15''$, and residual wide-field instrumental polarisation on the order of 0.1%. After de-duplication, our polarisation catalogue contains the detection of $2.5\times10^5$ ($3.4\times10^5$) Faraday rotation measures (RM) for components with a linearly polarised signal above $8\sigma$ ($6\sigma$). This places SPICE-RACS DR2 as the largest single RM catalogue ever produced by nearly an order of magnitude; the number of RMs in our catalogue alone is $\sim5$ times larger than every previous RM catalogue combined. Our resulting RM grid has an areal density of $6.7^{+1.8}_{-1.7}\mathrm{deg}^{-2}$, providing an effective 'resolution' of $\sim23'$, and reveals striking features across the sky. The broad-band RMs have a median uncertainty of $\sim2\ \mathrm{rad\ m}^{-2}$, and include complexity metrics and information from the time domain. The breadth and quality of the SPICE-RACS DR2 dataset will enable a new generation of RM science. Further, SPICE-RACS will provide an ideal reference for forthcoming deep polarisation surveys such as the ASKAP POSSUM survey. All of our data products are publicly available on the CSIRO Data Access Portal (DAP) and the CSIRO ASKAP Science Data Archive (CASDA).