Multi-wavelength properties of 850-$\mu$m selected sources from the
  North Ecliptic Pole SCUBA-2 survey
  We present the multi-wavelength counterparts of 850-$\mu$m selected
submillimetre sources over a 2-deg$^2$ field centred on the North Ecliptic
Pole. In order to overcome the large beam size (15 arcsec) of the 850-$\mu$m
images, deep optical to near-infrared (NIR) photometric data and
arcsecond-resolution 20-cm images are used to identify counterparts of
submillimetre sources. Among 647 sources, we identify 514 reliable counterparts
for 449 sources (69 per cent in number), based either on probabilities of
chance associations calculated from positional offsets or offsets combined with
the optical-to-NIR colours. In the radio imaging, the fraction of 850-$\mu$m
sources having multiple counterparts is 7 per cent. The photometric redshift,
infrared luminosity, stellar mass, star-formation rate (SFR), and the AGN
contribution to the total infrared luminosity of the identified counterparts
are investigated through spectral energy distribution fitting. The SMGs are
infrared-luminous galaxies at an average $\langle z\rangle=2.5$ with
$\mathrm{log}_{10} (L_\mathrm{IR}/\mathrm{L}_\odot)=11.5-13.5$, with a mean
stellar mass of $\mathrm{log}_{10} (M_\mathrm{star}/\mathrm{M}_\odot)=10.90$
and SFR of $\mathrm{log}_{10} (\mathrm{SFR/M_\odot\,yr^{-1}})=2.34$. The SMGs
show twice as large SFR as galaxies on the star-forming main sequence, and
about 40 per cent of the SMGs are classified as objects with bursty star
formation. At $z\ge4$, the contribution of AGN luminosity to total luminosity
for most SMGs is larger than 30 per cent. The FIR-to-radio correlation
coefficient of SMGs is consistent with that of main-sequence galaxies at
$z\simeq2$.
