The Evolution of the IR Luminosity Function and Dust-obscured Star
  Formation in the Last 13 Billion Years
  We present the first results from the 2mm Mapping Obscuration to Reionization
(MORA) survey, the largest ALMA contiguous blank-field survey to-date with a
total area of 184 sq. arcmin and the only at 2mm to search for dusty
star-forming galaxies (DSFGs). We use the 13 sources detected above 5sigma to
estimate the first ALMA galaxy number counts at this wavelength. These number
counts are then combined with the state-of-the-art galaxy number counts at
1.2mm and 3mm and with a backward evolution model to place constraints on the
evolution of the IR luminosity function and dust-obscured star formation in the
last 13 billion years. Our results suggest a steep redshift evolution on the
space density of DSFGs and confirm the flattening of the IR luminosity function
at faint luminosities, with a slope of $\alpha_{LF} = -0.42^{+0.02}_{-0.04}$.
We conclude that the dust-obscured component, which peaks at z=2-2.5, has
dominated the cosmic history of star formation for the past ~12 billion years,
back to z~4. At z=5, the dust-obscured star formation is estimated to be ~35%
of the total star formation rate density and decreases to 25%-20% at z=6-7,
implying a minor contribution of dust-enshrouded star formation in the first
billion years of the Universe. With the dust-obscured star formation history
constrained up to the end of the epoch of reionization, our results provide a
benchmark to test galaxy formation models, to study the galaxy mass assembly
history, and to understand the dust and metal enrichment of the Universe at
early times.
