Atomic Gas Dominates the Baryonic Mass of Star-forming Galaxies at z ≈ 1.3

We present a comparison between the average atomic gas mass, < M-Atom > (including hydrogen and helium), the average molecular gas mass, < M-Mol >, and the average stellar mass, < M-star >, of a sample of star-forming galaxies at z approximate to 0.75-1.45 to probe the baryonic composition of galaxies in and during the epoch of peak star formation activity in the universe. The < M-Atom > values of star-forming galaxies in two stellar-mass-matched samples at z = 0.74-1.25 and z = 1.25-1.45 were derived by stacking their Hi 21 cm signals in the GMRT-CATz1 survey. We find that the baryonic composition of star-forming galaxies at z greater than or similar to 1 is dramatically different from that at z approximate to 0. For star-forming galaxies with < M-star > approximate to 10(10) M-circle dot, the contribution of stars to the total baryonic mass, M-Baryon, is approximate to 61% at z approximate to 0, but only approximate to 16% at z approximate to 1.3, while molecular gas constitutes approximate to 6% of the baryonic mass at z approximate to 0, and approximate to 14% at z approximate to 1.3. Remarkably, we find that atomic gas makes up approximate to 70% of M-Baryon in star-forming galaxies at z approximate to 1.3. We find that the ratio < M-Atom >/< M-star > is higher at both z approximate to 1.3 and at z approximate to 1.0 than in the local universe, with < M-Atom >/< M star > approximate to 1.4 at z approximate to 1.0 and approximate to 4.4 at z approximate to 1.3, compared to its value of approximate to 0.5 today. Further, we find that the ratio < M-Atom >/< M-Mol > in star-forming galaxies with < M-star > approximate to 10(10) M-circle dot is approximate to 2.3 at z approximate to 1.0 and approximate to 5.0 at z approximate to 1.3. Overall, we find that atomic gas is the dominant component of the baryonic mass of star-forming galaxies at z approximate to 1.3, during the epoch of peak star formation activity in the universe.