  We use time-varying models of the coupled evolution of the HI, H_2 gas phases
and stars in galaxy-sized numerical simulations to: a) test for the emergence
of the Kennicutt-Schmidt (K-S) and the H_2-pressure relation, b) explore a
realistic H_2-regulated star formation recipe which brings forth a neglected
and potentially significant SF-regulating factor, and c) go beyond typical
galactic environments (for which these galactic empirical relations are
deduced) to explore the early evolution of very gas-rich galaxies. In this work
we model low mass galaxies ($M_{\rm baryon} \le 10^9 \msun$), while
incorporating an independent treatment of CO formation and destruction, the
most important tracer molecule of H2 in galaxies, along with that for the H2
gas itself. We find that both the K-S and the H_2-pressure empirical relations
can robustly emerge in galaxies after a dynamic equilibrium sets in between the
various ISM states, the stellar component and its feedback. (abridged)

Cosmology and Nongalactic Astrophysics