BLAST: the far-infrared/radio correlation in distant galaxies

R. J. Ivison, David M. Alexander, Andy D. Biggs, W. N. Brandt, Edward L. Chapin, Kristen E. K. Coppin, Mark J. Devlin, Mark Dickinson, James Dunlop, Simon Dye, Stephen A. Eales, David T. Frayer, Mark Halpern, David H. Hughes, Edo Ibar, A. Kovacs, Gaelen Marsden, L. Moncelsi, Calvin B. Netterfield, Enzo PascaleGuillaume Patanchon, D. A. Rafferty, Marie Rex, Eva Schinnerer, Douglas Scott, C. Semisch, Ian Smail, A. M. Swinbank, Matthew D. P. Truch, Gregory S. Tucker, Marco P. Viero, Fabian Walter, Axel Weiss, Donald V. Wiebe, Y. Q. Xue

Research output: Contribution to journalArticlepeer-review


We investigate the correlation between far-infrared (FIR) and radio luminosities in distant galaxies, a lynchpin of modern astronomy. We use data from the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), Spitzer, the Large Apex BOlometer CamerA (LABOCA), the Very Large Array and the Giant Metre-wave Radio Telescope (GMRT) in the Extended Chandra Deep Field South (ECDFS). For a catalogue of BLAST 250-mu m-selected galaxies, we remeasure the 70-870-mu m flux densities at the positions of their most likely 24-mu m counterparts, which have a median [interquartile] redshift of 0.74 [0.25, 1.57]. From these, we determine the monochromatic flux density ratio, q(250)(= log(10) [S-250 mu m/S-1400 MHz]), and the bolometric equivalent, q(IR). At z approximate to 0.6, where our 250-mu m filter probes rest-frame 160-mu m emission, we find no evolution relative to q(160) for local galaxies. We also stack the FIR and submm images at the positions of 24-mu m- and radio-selected galaxies. The difference between q(IR) seen for 250-mu m- and radio-selected galaxies suggests that star formation provides most of the IR luminosity in less than or similar to 100-mu Jy radio galaxies, but rather less for those in the mJy regime. For the 24-mu m sample, the radio spectral index is constant across 0 < z < 3, but q(IR) exhibits tentative evidence of a steady decline such that q(IR) proportional to (1 + z)-0.15 +/- 0.03 - significant evolution, spanning the epoch of galaxy formation, with major implications for techniques that rely on the FIR/radio correlation. We compare with model predictions and speculate that we may be seeing the increase in radio activity that gives rise to the radio background.

Original languageEnglish
Pages (from-to)245-258
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 11 Feb 2010


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