Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed
  submillimetre galaxy at z = 2.3
  We present a detailed analysis of the far-IR properties of the bright,
lensed, z = 2.3, SMG, SMM J2135-0102, using new observations with Herschel,
SCUBA-2 and the VLA. These data allow us to constrain the galaxy's SED and show
that it has an intrinsic rest-frame 8-1000um luminosity, L(bol), of (2.3 +/-
0.2) x 10^12 L(sun) and a likely SFR of ~400 M(sun)/yr. The galaxy sits on the
far-IR/radio correlation for far-IR-selected galaxies. At ~>70um, the SED can
be described adequately by dust components with T(d) ~ 30 and 60K. Using
SPIRE's Fourier Transform Spectrometer we report a detection of the [CII] 158um
cooling line. If the [CII], CO and far-IR continuum arise in photo-dissociation
regions, we derive a characteristic gas density, n ~ 10^3 cm^-3, and a far-UV
radiation field, G_0, 10^3x stronger than the Milky Way. L([CII])/L(bol) is
significantly higher than in local ULIRGs but similar to the values found in
local star-forming galaxies and starburst nuclei. This is consistent with SMM
J2135-0102 being powered by starburst clumps distributed across ~2 kpc,
evidence that SMGs are not simply scaled-up ULIRGs. Our results show that
SPIRE's FTS has the ability to measure the redshifts of distant, obscured
galaxies via the blind detection of atomic cooling lines, but it will not be
competitive with ground-based CO-line searches. It will, however, allow
detailed study of the integrated properties of high-redshift galaxies, as well
as the chemistry of their ISM, once more suitably bright candidates have been
found.
