Exploring the infrared/radio correlation at high redshift

Abstract

We have analysed the 24um properties of a radio-selected sample in the Subaru-XMM/Newton Deep Field in order to explore the behaviour of the FIR/radio relation at high redshifts. Statistically, the correlation is described by q24, the ratio between the observed flux densities at 24um and 1.4GHz, respectively. Using 24um data results in considerably more scatter in the correlation than previous work using data at 60-70um. Nevertheless, we do observe a steady correlation as a function of redshift, up to z~3.5, suggesting its validity back to primeval times. We find q24 = 0.30 +/- 0.56 for the observed and q24 = 0.71 +/- 0.47 for the k-corrected radio sample, based on sources with 300uJy < S(1.4GHz) < 3.2mJy and 24um detections. A suitable k-correction given by a M82-like mid-IR template suggests no extreme silicate absorption in the bulk of our radio sample. Using thresholds in q24 to identify radio-excess sources, we have been able to characterise the transition from radio-loud AGN to star-forming galaxies and radio-quiet AGN at faint (<1mJy) radio flux densities. Our results are in broad agreement with previous studies which show a dominant radio-loud AGN population at >1mJy. The rest-frame U-B colours of the expected radio-excess population have redder distribution than those that follow the correlation. This is therefore a promising way to select obscured Type-2 AGN, with a radio loud nature, missed by deep X-ray observations. Spectroscopic follow-up of these sources is required to fully test this method.

The paper contains 7 figures and 1 table. In press at MNRAS

References in corpus (4)

• The SCUBA HAlf Degree Extragalactic Survey (SHADES) - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies
• Extending the infrared radio correlation
• Galaxy Counts at 24 Microns in the SWIRE Fields
• Deep 610-MHz GMRT observations of the Spitzer extragalactic First Look Survey field - I. Observations, data analysis and source catalogue

Cited by in corpus (10)

• HiZELS: a high redshift survey of H-alpha emitters. I: the cosmic star-formation rate and clustering at z=2.23
• The star-formation history of K-selected galaxies
• A new model for infrared and submillimetre counts
• Star formation rates in Lyman break galaxies: radio stacking of LBGs in the COSMOS field and the sub-$\mu$Jy radio source population
• Obscuring Active Galactic Nuclei with Nuclear Starburst Disks
• A Millimetre Survey of Starburst Dominated Ultraluminous Infrared Galaxies at z~2
• A 610-MHz survey of the Lockman Hole with the Giant Metrewave Radio Telescope - I. Observations, data reduction and source catalogue for the central 5 square degrees
• Radio source stacking and the infrared / radio correlation at microJy flux densities
• Multi-wavelength properties of Spitzer-selected starbursts at z~2
• Radio and X-ray properties of submillimeter galaxies in the A2125 field