Radio Polarimetry of the ELAIS N1 Field: Polarized Compact Sources

TL;DR

This study conducts deep polarimetric radio observations of the ELAIS N1 field, revealing properties of polarized compact sources, their polarization levels, and host galaxy types, with implications for understanding faint polarized radio source populations.

Contribution

It provides the first deep polarization survey of the ELAIS N1 field, characterizing faint polarized sources and their host galaxy properties at 1420 MHz.

Findings

Faint polarized sources are more highly polarized than brighter ones.

Median fractional polarization is about 4.8% for sources with 1-30 mJy flux.

Most polarized sources are associated with dusty AGNs or ellipticals, few with star-forming galaxies.

Abstract

We present deep polarimetric observations at 1420 MHz of the European Large Area ISO Survey North 1 region (ELAIS N1) as part of the Dominion Radio Astrophysical Observatory Planck Deep Fields project. By combining closely spaced aperture synthesis fields, we image a region of 7.43 square degrees to a maximum sensitivity in Stokes Q and U of 78 microJy/beam, and detect 786 compact sources in Stokes I. Of these, 83 exhibit polarized emission. We find that the differential source counts (log N - log p) for polarized sources are nearly constant down to p > 500 microJy, and that these faint polarized radio sources are more highly polarized than the strong source population. The median fractional polarization is (4.8 +/- 0.7)% for polarized sources with Stokes I flux density between 1 and 30 mJy; approximately three times larger than sources with I > 100 mJy. The majority of the polarized sources have been identified with galaxies in the Spitzer Wide Area Infrared Extragalactic Survey (SWIRE) image of ELAIS N1. Most of the galaxies occupy regions in the IRAC 5.8/3.6 micron vs. 8.0/4.5 micron color-color diagram associated with dusty AGNs, or with ellipticals with an aging stellar population. A few host galaxies have colors that suggests significant PAH emission in the near-infrared. A small fraction, 12%, of the polarized sources are not detected in the SWIRE data. None of the polarized sources in our sample appears to be associated with an actively star-forming galaxy.