Abstract
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 language | English |
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Pages (from-to) | 1-25 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 337 |
DOIs | |
Publication status | Published - 1 Nov 2002 |