Observational Evidence For Constant Gas Accretion Rate Since z = 5
  Star formation rate density (SFRD) has not been constant throughout the
history of the Universe. The rate at which stars form greatly affects the
evolution of the Universe, but the factors which drive SFRD evolution remain
uncertain. There must be sufficient amount of gas to fuel the star formation,
either as a reservoir within a galaxy, or as inflow from the intergalactic
medium (IGM). This work explores how the gas accretion rate onto galaxies over
time has affected star formation rate. We propose a novel method of measuring
cosmic gas accretion rate. This involves comparing the comoving densities of
available Hi and H2 gas and the densities of existing stars at different
redshifts. We constrained gas accretion until z = 5, and we found that the gas
accretion rate density (GARD) is relatively constant in the range from z = 5 to
z = 0. This constancy in the GARD is not reflected by the SFRD, which declines
significantly between z = 1.0 and z = 0. This work suggests that the decline is
not due to a reduction in GARD.
