Deep radio imaging of the SCUBA 8-mJy survey fields: submillimetre source identifications and redshift distribution

R. J. Ivison, T. R. Greve, Ian Smail, J. S. Dunlop, N. D. Roche, S. E. Scott, M. J. Page, J. A. Stevens, O. Almaini, A. W. Blain, C. J. Willott, M. J. Fox, D. G. Gilbank, S. Serjeant, D. H. Hughes

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The SCUBA 8-mJy survey is the largest submillimetre (submm) extragalactic mapping survey undertaken to date, covering 260 arcmin2 to a 4 σ detection limit of ~=8 mJy at 850 μm, centred on the Lockman Hole and ELAIS N2 regions. Here, we present the results of new 1.4-GHz imaging of these fields, of the depth and resolution necessary to reliably identify radio counterparts for 18 of 30 submm sources, with possible detections of a further 25 per cent. Armed with this greatly improved positional information, we present and analyse new optical, near-infrared (near-IR) and XMM-Newton X-ray imaging to identify optical/IR host galaxies to half of the submm-selected sources in those fields. As many as 15 per cent of the submm sources detected at 1.4 GHz are resolved by the 1.4-arcsec beam and a further 25 per cent have more than one radio counterpart, suggesting that radio and submm emission arise from extended starbursts and that interactions are common. We note that less than a quarter of the submm-selected sample would have been recovered by targeting optically faint radio sources, underlining the selective nature of such surveys. At least 60 per cent of the radio-confirmed optical/IR host galaxies appear to be morphologically distorted; many are composite systems - red galaxies with relatively blue companions; just over one half are found to be very red (I - K > 3.3) or extremely red (I - K > 4); contrary to popular belief, most are sufficiently bright to be tackled with spectrographs on 8-m telescopes. We find one submm source which is associated with the steep-spectrum lobe of a radio galaxy, at least two more with flatter radio spectra typical of radio-loud active galactic nuclei (AGN), one of them variable. The latter is amongst four sources (≡15 per cent of the full sample) with X-ray emission consistent with obscured AGN, though the AGN would need to be Compton thick to power the observed far-IR luminosity. We exploit our well-matched radio and submm data to estimate the median redshift of the S850μm ~ 8 mJy submm galaxy population. If the radio/far-IR correlation holds at high redshift, and our sample is unbiased, we derive a conservative limit of <z> >=2.0, or >=2.4 using spectral templates more representative of known submm galaxies.
Original languageEnglish
Pages (from-to)1-25
JournalMonthly Notices of the Royal Astronomical Society
Volume337
DOIs
Publication statusPublished - 1 Nov 2002

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