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
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 deg2 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 (q 24 and q 70), as well as the ratio of the total IR and the 1.4 GHz luminosity (q TIR), 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.
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- February 2010
- DOI:
- 10.1088/0067-0049/186/2/341
- arXiv:
- arXiv:1001.1354
- Bibcode:
- 2010ApJS..186..341S
- Keywords:
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- cosmology: observations;
- galaxies: active;
- galaxies: evolution;
- galaxies: high-redshift;
- infrared: galaxies;
- radio continuum: galaxies;
- surveys;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 52 pages, 23 figures (11 at reduced resolution). Accepted for publication in ApJS