The VLA-COSMOS Survey - V. 324 MHz continuum observations

Smolčić, Vernesa and Ciliegi, Paolo and Jelić, Vibor and Bondi, Marco and Schinnerer, Eva and Carilli, Chris L. and Riechers, Dominik A. and Salvato, Mara and Brković, Alen and Capak, Peter and Ilbert, Olivier and Karim, Alexander and McCracken, Henry and Scoville, Nick Z. (2014) The VLA-COSMOS Survey - V. 324 MHz continuum observations. Monthly Notices of the Royal Astronomical Society, 443 (3). pp. 2590-2598. ISSN 0035-8711

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We present 90 cm Very Large Array imaging of the COSMOS field, comprising a circular area of 3.14 square degrees at 8.0arcsec × 6.0arcsec angular resolution with an average rms of 0.5 mJy beam^(−1). The extracted catalogue contains 182 sources (down to 5.5σ), 30 of which are multicomponent sources. Using Monte Carlo artificial source simulations, we derive the completeness of the catalogue, and we show that our 90 cm source counts agree very well with those from previous studies. Using X-ray, NUV–NIR and radio COSMOS data to investigate the population mix of our 90 cm radio sample, we find that our sample is dominated by active galactic nuclei. The average 90–20 cm spectral index (S_ν ∝ ν^α, where S_ν is the flux density at frequency ν and α the spectral index) of our 90 cm selected sources is −0.70, with an interquartile range from −0.90 to −0.53. Only a few ultra-steep-spectrum sources are present in our sample, consistent with results in the literature for similar fields. Our data do not show clear steepening of the spectral index with redshift. Nevertheless, our sample suggests that sources with spectral indices steeper than −1 all lie at z ≳ 1, in agreement with the idea that ultra-steep-spectrum radio sources may trace intermediate-redshift galaxies (z ≳ 1).

Item Type: Article
Keywords: radiation mechanisms: general, surveys, radio continuum: galaxies
Date: 21 September 2014
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 July 1. Received 2014 June 23; in original form 2014 April 1.
Divisions: Faculty of Science > Department of Physics
Publisher: Oxford University Press
Depositing User: Vernesa Smolčić
Date Deposited: 11 May 2016 19:11
Last Modified: 14 Oct 2016 07:00

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