DEVIATIONS FROM THE SCHMIDT-KENNICUTT RELATIONS DURING EARLY GALAXY EVOLUTION

We utilize detailed time-varyingmodels of the coupled evolution of stars and the H-1, H-2, and CO-bright H-2 gas phases in galaxy-sized numerical simulations to explore the evolution of gas-rich and/or metal-poor systems, which are expected to be numerous in the early universe. The inclusion of the CO-bright H-2 gas phase and the realistic rendering of star formation as an H-2-regulated process (and the new feedback processes that this entails) allow the most realistic tracking of strongly evolving galaxies and much better comparison with observations. We find that while galaxies eventually settle into states conforming to the Schmidt-Kennicutt (S-K) relations, significant and systematic deviations of their star formation rates (SFRs) from the latter occur, and are especially pronounced and prolonged for metal-poor systems. The largest such deviations occur for gas-rich galaxies during not only the early evolutionary stages but also during brief periods at later stages. Given that gas-rich and/or metal-poor states of present-epoch galaxies are expected in the early universe while a much larger number of mergers frequently reset non-isolated systems to gas-rich states, even brief periods of sustained deviations of their SFRs from those expected from the S-K relations may come to characterize significant periods of their stellar mass built-up. This indicates potentially serious limitations of S-K-type relations as reliable sub-grid elements of star formation physics in simulations of structure formation in the early universe. We anticipate that galaxies with marked deviations from the S-K relations will be found at high redshifts as unbiased inventories of total gas mass become possible with ALMA and the EVLA.