Evolution of the atomic and molecular gas content of galaxies

Abstract

We study the evolution of atomic and molecular gas in galaxies in semi-analytic models of galaxy formation that include new modeling of the partitioning of cold gas in galactic discs into atomic, molecular, and ionised phases. We adopt two scenarios for the formation of molecules: one pressure-based and one metallicity-based. We find that both recipes successfully reproduce the gas fractions and gas-to-stellar mass ratios of Hi and H 2 in local galaxies, as well as the Hi and H 2 disc sizes up to z 2. We reach good agreement with the locally observed Hi and H 2 mass function, although both recipes slightly overpredict the low-mass end of the Hi mass function. Both of our models predict that the high-mass end of the Hi mass function remains nearly constant at redshifts z < 2.0. The metallicity-based recipe yields a higher cosmic density of cold gas and much lower cosmic H 2 fraction over the entire redshift range probed than the pressure based recipe. These strong differences in Hi mass function and cosmic density between the two recipes are driven by low mass galaxies (log (M * /M ⊙ ) 7) residing in low mass halos (log (M vir /M ⊙ ) 10). Both recipes predict that galaxy gas fractions remain high from z ∼ 6 − 3 and drop rapidly at lower redshift. The galaxy H 2 fractions show a similar trend, but drop even more rapidly. We provide predictions for the CO J = 1 − 0 luminosity of galaxies, which will be directly comparable with observations with sub-mm and radio instruments.

Redshift evolution of stellar mass versus gas fraction relation in 0 <z< 2 regime: observational constraint for galaxy formation models

“…The observational studies essentially tend to be biased towards bright objects such as gas-rich objects and/or optically bright objects if the targets are selected based on large optical surveys. It has been claimed that the models reproduce the observational results relatively well if they take into account the sample selection criteria and observational sensitivities Popping et al 2014). These studies showed that the predicted fH 2 value approaches the observed value if these observational conditions are considered, but there still seem to be discrepancies between observations and model predictions (see Fig.…”

“…These studies showed that the predicted fH 2 value approaches the observed value if these observational conditions are considered, but there still seem to be discrepancies between observations and model predictions (see Fig. 11 in Popping et al 2014). In addition, a gap between a semi-empirical model, as a proxy for observations, and theoretical predictions was also reported .…”

“…Schaye et al 2010Schaye et al , 2015Okamoto et al 2014;Thompson et al 2014;Vogelsberger et al 2014). In addition, some of these theoretical studies have implemented the equilibrium or non-equilibrium formation of H2, as well as star formation from such H2 gas, in cosmological simulations (Gnedin et al 2009;Christensen et al 2012;Thompson et al 2014;Tomassetti et al 2015) and SAMs (Lagos et al 2011b;Fu et al 2012;Popping et al 2014;Somerville et al 2015).…”

SIMULATOR OF GALAXY MILLIMETER/SUBMILLIMETER EMISSION (SÍGAME): THE [C ii]–SFR RELATIONSHIP OF MASSIVEz= 2 MAIN SEQUENCE GALAXIES

“…Figure 9). Employing a semi-analytical model of galaxy formation, Popping et al (2014a) Popping et al 2014b). The galaxies are assumed to have exponential disk gas density profiles, with randomly placed "over-densities" mimicking GMCs (constituting~1% of the total volume).…”

The Alma Spectroscopic Survey in the Hubble Ultra Deep Field: Molecular Gas Reservoirs in High-Redshift Galaxies

“…This might reflect the large variations in gas content of disk galaxies seen in semianalytical models (see, e.g., Lagos et al 2011 and Figure 9 in Popping et al 2014). Perhaps not unexpectedly, global scaling relations cannot account for the large variations in gas content in individual high-redshift galaxies.…”