Zusammenfassung
Cold hydrogen gas is the raw fuel for star formation in galaxies, and its
partition into atomic and molecular phases is a key quantity for galaxy
evolution. In this paper, we combine Atacama Large Millimeter Array and Arecibo
single-dish observations to estimate the molecular-to-atomic hydrogen mass
ratio for massive star-forming galaxies at $z\sim$ 0.2 extracted from the HIGHz
survey, i.e., some of the most massive gas-rich systems currently known. We
show that the balance between atomic and molecular hydrogen in these galaxies
is similar to that of local main-sequence disks, implying that atomic hydrogen
has been dominating the cold gas mass budget of star-forming galaxies for at
least the last three billion years. In addition, despite harboring gas
reservoirs that are more typical of objects at the cosmic noon, HIGHz galaxies
host regular rotating disks with low gas velocity dispersions suggesting that
high total gas fractions do not necessarily drive high turbulence in the
interstellar medium.
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