Properties of Polarized Radio Sources in the Wide Chandra Deep Field South from 2 to 4GHz

Abstract

We present a study of the linear polarization properties of radio sources within the 10 deg$^2$ Wide Chandra Deep Field South (W-CDFS) in S-band (2-4 GHz). Our W-CDFS image has an angular resolution of 15 arcsec and a 1$σ$ RMS in Stokes $I$ of $\approx$50 $μ$Jy/beam. We detect 1920 distinct source components in Stokes $I$ and 175 in linear polarization. We examine the polarized source counts, Faraday Rotation measures, and fractional polarization of the sources in the survey. We show that sources with a total intensity above $\approx$10mJy have a mean fractional polarization value of $\approx$3% from modeling the polarized counts. We also calculate an estimate for the limit on the fractional polarization level of sources with a total intensity below 1mJy (mostly star-forming galaxies) of $\stackrel{<}{_{\sim}}$3% using stacking. The mean Faraday Rotation we measure is consistent with that due to the Milky Way. We also show that fractional polarization is correlated with in-band spectral index, consistent with a lower mean fractional polarization for the flat-spectrum population. In addition to characterizing the S-band polarization properties of sources in the W-CDFS, this study will be used to validate the shallower, but higher angular resolution S-band polarimetric information that the VLA Sky Survey will provide for the whole sky above Declination -40 degrees over the next few years.

Figures (2)

• Figure S1: Surveys covering $>$1 deg$^{2}$ in the W-CDFS, overlaid on the Stokes $I$ image from this paper (greyscale). Left: X-ray through near-infrared. The XMM-Newton XMM-SERVS survey 2021ApJS..256...21N covers the footprint of the near-infrared VIDEO survey 2013MNRAS.428.1281J in solid red. The LSST deep-drilling field is represented by the black circle, which is also the footprint covered by the warm Spitzer 3.6 $\upmu$m and 4.5 $\upmu$m data 2021MNRAS.501..892L2022AA...658A.126E. Further near-infrared data are provided by VEILS (orange, right-hatched 2017MNRAS.464.1693H), which, together with VIDEO, covers the footprint of the Dark Energy Survey supernova fields in W-CDFS. W-CDFS also has deep optical imaging from the HyperSuprimeCam SSP survey (green, left-hatched 2018PASJ...70S...4A). Right: Mid- and far-infrared and radio surveys, with the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) 24 $\upmu$m coverage (magenta, right-hatched 2003PASP..115..897L), the Herschel Multi-tiered Extragalactic Survey (HeRMES) (green, left-hatched 2012MNRAS.424.1614O) and the 1.4 GHz component of the Australia Telescope Large Area Survey (ATLAS) (red circle speckled 2014MNRAS.441.2555H). See 2021MNRAS.501..892L for more details and other surveys in this field.
• Figure S2: (Upper panel) counts of linear polarization and total intensity for the source components in the survey and in other $\approx$3 GHz surveys in the literature as detailed in Section \ref{['sec:imaging']}. The full survey areas are used in all cases. The two models of the polarized counts correspond to the model of Equation \ref{['eqn:polcts']}, with the dotted line having the characteristic polarization fraction that matches the 1.4 GHz population and the dashed one the best fit to our S-band data. (Lower panel) Detail of the total intensity counts, focusing on the region of overlap of the COSMOS, VLASS, and SPASS counts with those from this paper.