Tracing the evolution of dust-obscured activity using sub-millimetre
  galaxy populations from STUDIES and AS2UDS
  We analyse the physical properties of 121 SNR $\geq$ 5 sub-millimetre
galaxies (SMGs) from the STUDIES 450-$\mu$m survey. We model their UV-to-radio
spectral energy distributions using MAGPHYS+photo-$z$ and compare the results
to similar modelling of 850-$\mu$m-selected SMG sample from AS2UDS, to
understand the fundamental physical differences between the two populations at
the observed depths. The redshift distribution of the 450-$\mu$m sample has a
median of $z$ = 1.85 $\pm$ 0.12 and can be described by strong evolution of the
far-infrared luminosity function. The fainter 450-$\mu$m sample has $\sim$14
times higher space density than the brighter 850-$\mu$m sample at $z$
$\lesssim$2, and a comparable space density at $z$ = 2-3, before rapidly
declining, suggesting LIRGs are the main obscured population at $z$ $\sim$ 1-2,
while ULIRGs dominate at higher redshifts. We construct rest-frame $\sim$
180-$\mu$m-selected and dust-mass-matched samples at $z$ = 1-2 and $z$ = 3-4
from the 450-$\mu$m and 850-$\mu$m samples, respectively, to probe the
evolution of a uniform sample of galaxies spanning the cosmic noon era. Using
far-infrared luminosity, dust masses and an optically-thick dust model, we
suggest that higher-redshift sources have higher dust densities due to inferred
dust continuum sizes which are roughly half of those for the lower-redshift
population at a given dust mass, leading to higher dust attenuation. We track
the evolution in the cosmic dust mass density and suggest that the dust content
of galaxies is governed by a combination of both the variation of gas content
and dust destruction timescale.
