The VLA-cosmos perspective on the infrared-radio relation. I. New constraints on selection biases and the non-evolution of the infrared/radio properties of star-forming and active galactic nucleus galaxies at intermediate and high redshift

Sargent, M T and et al, (2010) The VLA-cosmos perspective on the infrared-radio relation. I. New constraints on selection biases and the non-evolution of the infrared/radio properties of star-forming and active galactic nucleus galaxies at intermediate and high redshift. Astrophysical Journal Supplement Series, 186 (2). pp. 341-377. ISSN 0067-0049

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Abstract

VLA 1.4 GHz (σ~0.012 mJy) and MIPS 24 and 70 μm (σ~0.02 and 1.7 mJy, respectively) observations covering the 2 sqdeg COSMOS field are combined with an extensive multiwavelength data set to study the evolution of the infrared (IR)-radio relation at intermediate and high redshift. With ~4500 sources—of which ~30% have spectroscopic redshifts—the current sample is significantly larger than previous ones used for the same purpose. Both monochromatic IR/radio flux ratios (q24 and q70), as well as the ratio of the total IR and the 1.4 GHz luminosity (qTIR), are used as indicators for the IR/radio properties of star-forming galaxies and active galactic nuclei (AGNs). Using a sample jointly selected at IR and radio wavelengths in order to reduce selection biases, we provide firm support for previous findings that the IR-radio relation remains unchanged out to at least z~1.4. Moreover, based on data from ~150 objects we also find that the local relation likely still holds at zin [2.5, 5]. At redshift z<1.4, we observe that radio-quiet AGNs populate the locus of the IR-radio relation in similar numbers as star-forming sources. In our analysis, we employ the methods of survival analysis in order to ensure a statistically sound treatment of flux limits arising from non-detections. We determine the observed shift in average IR/radio properties of IR- and radio-selected populations and show that it can reconcile apparently discrepant measurements presented in the literature. Finally, we also investigate variations of the IR/radio ratio with IR and radio luminosity and find that it hardly varies with IR luminosity but is a decreasing function of radio luminosity.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Mark Sargent
Date Deposited: 12 Sep 2013 14:46
Last Modified: 22 Mar 2017 17:43
URI: http://sro.sussex.ac.uk/id/eprint/46168

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