Exploring the infrared/radio correlation at high redshift

Edo Ibar, Michele Cirasuolo, Rob Ivison, Philip Best, Ian Smail, Andy Biggs, Chris Simpson, Jim Dunlop, Omar Almaini, Ross McLure, Sebastien Foucaud, Steve Rawlings

Research output: Contribution to journalArticlepeer-review

Abstract

We have analysed the 24-mu m properties of a radio-selected sample in the Subaru-XMM-Newton Deep Field in order to explore the behaviour of the far-infrared/radio (FIR/radio) relation at high redshifts. Statistically, the correlation is described by q(24), the ratio between the observed flux densities at 24 mu m and 1.4 GHz, respectively. Using 24-mu m data results in considerably more scatter in the correlation than previous work using data at 60-70 mu m. Nevertheless, we do observe a steady correlation as a function of redshift, up to z approximate to 3.5, suggesting its validity back to primeval times. We find q(24) = 0.30 +/- 0.56 for the observed and q(24) = 0.71 +/- 0.47 for the k-corrected radio sample, based on sources with 300 mu Jy < S-1.4 GHz < 3.2 mJy and 24-mu m detections. A suitable k-correction given by a M82-like mid-infrared (mid-IR) template suggests no extreme silicate absorption in the bulk of our radio sample. Using thresholds in q(24) to identify radio-excess sources, we have been able to characterize the transition from radio-loud active galactic nuclei (AGN) to star-forming galaxies and radio-quiet AGN at faint (less than or similar to 1 mJy) radio-flux densities. Our results are in broad agreement with previous studies which show a dominant radio-loud AGN population at > 1 mJy. The rest-frame U- B colours of the expected radio-excess population have a 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.

Original languageEnglish
Pages (from-to)953-962
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume386
Issue number2
DOIs
Publication statusPublished - 11 May 2008

Keywords

  • galaxies
  • active
  • fundamental parameters
  • high-redshift
  • starburst
  • STAR-FORMING GALAXIES
  • EARLY DATA RELEASE
  • SUBMILLIMETER GALAXIES
  • LUMINOSITY FUNCTION
  • DEEP-FIELD
  • MU-M
  • COSMOLOGICAL EVOLUTION
  • ENERGY-DISTRIBUTIONS
  • EXTRAGALACTIC SURVEY
  • RADIO-SOURCES

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