The SCUBA-2 Cosmology Legacy Survey: demographics of the 450 \mu
  m-population
  We investigate the multi-wavelength properties of a sample of 450-\mu m
selected sources from the SCUBA-2 Cosmology Legacy Survey (S2CLS). A total of
69 sources were identified above 4\sigma\ in deep SCUBA-2 450-\mu m
observations overlapping the UDS and COSMOS fields and covering 210 sq. arcmin
to a typical depth of \sigma 450=1.5 mJy. Reliable cross identification are
found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope
WFC3/IR data. The photometric redshift distribution (dN/dz) of 450\mu
m-selected sources is presented, showing a broad peak in the redshift range
1<z<3, and a median of z=1.4. Combining the SCUBA-2 photometry with Herschel
SPIRE data from HerMES, the submm spectral energy distribution (SED) is
examined via the use of modified blackbody fits, yielding aggregate values for
the IR luminosity, dust temperature and emissivity of <LIR>=10^12 +/- 0.8
L_sol, <T_D>=42 +/- 11 K and <\beta_D>=1.6 +/- 0.5, respectively. The
relationship between these SED parameters and the physical properties of
galaxies is investigated, revealing correlations between T_D and LIR and
between \beta_D and both stellar mass and effective radius. The connection
between star formation rate and stellar mass is explored, with 24 per cent of
450 \mu m sources found to be ``star-bursts'', i.e. displaying anomalously high
specific SFRs. However, both the number density and observed properties of
these ``star-burst'' galaxies are found consistent with the population of
normal star-forming galaxies.
