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.Comment: 28 pages, 8 Figures. Figures 2 and 3 as separate gif images. Accepted for publication in the Astrophysical Journa

We present results of deep polarization imaging at 1.4 GHz with the Dominion Radio Astrophysical Observatory as part of the DRAO Planck Deep Fields project. This deep extragalactic field covers 15.16 deg 2 centered at α 2000 = 16 h 14 m and δ 2000 = 54 • 56 ′ , has an angular resolution of 42 ′′ × 62 ′′ at the field center, and reaches a sensitivity of 55 µJy beam −1 in Stokes I and 45 µJy beam −1 in Stokes Q and U. We detect 958 radio sources in Stokes I of which 136 are detected in polarization. We present the Euclidean-normalized polarized differential source counts down to 400 µJy. These counts indicate that sources have a higher degree of fractional polarization at fainter Stokes I flux density levels than for brighter sources, confirming an earlier result. We find that the majority of our polarized sources are steep-spectrum objects with a mean spectral index of −0.77, and there is no correlation between fractional polarization and spectral index. We also matched deep field sources to counterparts in the Faint Images of the Radio Sky at Twenty Centimeters catalogue. Of the polarized sources, 77% show structure at the arc-second scale whereas only 38% of the sources with no detectable polarization show such structure. The median fractional polarization is for resolved sources is 6.8%, while it is 4.4% for compact objects. The polarized radio sources in our deep field are predominantly those sources which are resolved and show the highest degrees of fractional polarization, indicating that the lobe dominated structure may be the source of the highly polarized sources. These resolved radio galaxies dominate the polarized source counts at P 0 = Q 2 + U 2 < 3 mJy.

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We compare the structural properties of two classes of galaxies at intermediate redshift: those in dynamically close galaxy pairs, and those that are isolated. Both samples are selected from the Canadian Network for Observational Cosmology field galaxy redshift survey (CNOC2) and have redshifts in the range 0:1< z < 0:6. Hubble Space Telescope WFPC2 images were acquired as part of a snapshot survey and were used to measure bulge fraction and asymmetry for these galaxies. We find that paired and isolated galaxies have identical distributions of bulge fractions. Conversely, we find that paired galaxies are much more likely to be asymmetric (R T þ R A ! 0:13) than isolated galaxies. Assuming that half of these pairs are unlikely to be close enough to merge, we estimate that 40% AE 11% of merging galaxies are asymmetric, compared with 9% AE 3% of isolated galaxies. The difference is even more striking for strongly asymmetric (R T þ R A ! 0:16) galaxies: 25% AE 8% for merging galaxies versus 1% AE 1% for isolated galaxies. We find that strongly asymmetric paired galaxies are very blue, with rest-frame BÀR colors close to 0.80, compared with a mean (BÀR) 0 of 1.24 for all paired galaxies. In addition, asymmetric galaxies in pairs have strong [O ii] k3727 emission lines. We conclude that close to half of the galaxy pairs in our sample are in the process of merging and that most of these mergers are accompanied by triggered star formation.

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