SCUBA-2 Ultra Deep Imaging Eao Survey (Studies) III: Multi-wavelength properties, luminosity functions and preliminary source catalog of 450-$\mu$m-selected galaxies

We construct a SCUBA-2 450-$\mu$m map in the COSMOS field that covers an area of 300 arcmin${}^2$ and reaches a 1$\sigma$ noise level of 0.65 mJy in the deepest region. We extract 256 sources detected at 450 $\mu$m with signal-to-noise ratio $>$ 4.0 and analyze the physical properties of their multi-wavelength counterparts. We find that most of the sources are at $z\lesssim 3$, with a median of $z=1.79_{-0.15}^{+0.03}$. About $35_{-25}^{+32}$% of our sources are classified as starburst galaxies based on their total star-formation rates (SFRs) and stellar masses ($M_{\ast }$). By fitting the far-infrared spectral energy distributions, we find that our 450-$\mu$m-selected sample has a wide range of dust temperatures (20 K $\lesssim T_{\mathrm{d}}\lesssim$ 60 K), with a median of ${T}{\rm d} = 38.3^{+0.4}{-0.9}$ K. We do not find a redshift evolution in dust temperature for sources with $L_{\mathrm{I}\mathrm{R}}$ > ${10}^{12}$ ${\mathrm{L}}_{\odot }$ at $z<3$. However, we find a moderate correlation where dust temperature increases with the deviation from the SFR-$M_{\ast }$ relation. The increase in dust temperature also correlates with optical morphology, which is consistent with merger-triggered starbursts in sub-millimeter galaxies. Our galaxies do not show the tight IRX-${\beta }_{\mathrm{U}\mathrm{V}}$ correlation that has been observed in the local Universe. We construct the infrared luminosity functions of our 450-$\mu$m sources and measure their comoving SFR densities. The contribution of the $L_{\mathrm{I}\mathrm{R}}$ > ${10}^{12}$ ${\mathrm{L}}_{\odot }$ population to the SFR density rises dramatically from $z$ = 0 to 2 ($\propto$ ($1+z$)${}^{3.9\pm 1.1}$) and dominates the total SFR density at $z\gtrsim 2$.