The rise and fall of dust in the Universe

We estimate how the mean density of dust in the Universe varies with redshift, using submillimetre continuum observations and a method designed to minimize the effect of dust temperature. We have used the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) to show that the median temperature of dust in galaxies is $\simeq 22\ \mathrm{ K}$ and does not vary significantly with redshift out to z = 1. With this as our estimate of the mass-weighted dust temperature, we have used an 850-μm survey of the field of the Cosmological Evolution Survey (COSMOS) to estimate the mean density of dust in 10 redshift bins over the range 0 < z < 5.5. We find that the mean density of dust increased by a factor of ≃10 from z = 5 to z = 2, declined slightly to z = 1, and then steeply to the present day. The relationship between the mean density of dust and redshift is similar to the relationship between the mean star formation rate and redshift, although the increase for the former is steeper from z = 5 to z = 2. We have also used the submillimetre measurements to estimate the mean density of gas over the same redshift range. The values we estimate for the dust-traced gas are much lower and with a different redshift dependence than those for estimates of the mean density of atomic gas but similar to those for estimates of the mean density of the CO-traced gas. We find that the depletion time for the dust-traced gas in the Universe as a whole declines with redshift in the same way as seen for individual galaxies.