We construct a SCUBA-2 450- \micron 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 \micron 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 ^ { +0.03 } _ { -0.15 } .
About 35 ^ { +32 } _ { -25 } % 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- \micron -selected sample has a wide range of dust temperatures ( 20 K \lesssim T _ { d } \lesssim 60 K ) , with a median of { T } _ { d } = 38.3 ^ { +0.4 } _ { -0.9 } K. We do not find a redshift evolution in dust temperature for sources with L _ { IR } > 10 ^ { 12 } L _ { \sun } 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 _ { UV } correlation that has been observed in the local Universe .
We construct the infrared luminosity functions of our 450- \micron sources and measure their comoving SFR densities .
The contribution of the L _ { IR } > 10 ^ { 12 } L _ { \sun } 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 .