Cosmological Evolution of the Universe Neutral Gas Mass Measured by Quasar Adsorption Systems

The cosmological evolution of neutral hydrogen is an efficient way of tracing structure formation with redshift. It indicates the rate of evolution of gas into stars and hence the gas consumption and rate star formation history of the Universe. In measuring HI, quasar absorbers have proven to be an ideal tool and we use observations from a recent survey for high-redshift quasar absorption systems together with data gathered from the literature to measure the cosmological comoving mass density of neutral gas. This paper assumes Ω_M =0.3, Ω_Λ=0.7 and h=0.65.