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8. WHAT SHOULD A MODEL OF STAR FORMATION BE FOR HIGH REDSHIFT GALAXIES?

Young galaxies look like their whole disk is out of equilibrium. In general terms, the star formation rate is expected to equal the accretion rate. This implies that if simple laws like the KS relation or the Bigiel-Leroy relation apply, then they fix the gas column density or molecular column density for a given star formation rate, not the other way around. Maybe the molecular abundance still depends on pressure and the radiation field, and maybe stars still form only in molecular gas, but if the star formation rate is pinned to the accretion rate, then these local relations are not useful and in predicting the star formation rate. Perhaps the growth rate of GMCs equals the accretion rate by a whole galaxy. This would seem to be necessary to maintain a steady state. In a broad sense, this situation is like the dynamical triggering models discussed in these Lectures earlier, i.e., the spiral-wave or shell-like organization of gas into star-forming regions. Instead of spiral waves and shells collecting matter on a kpc scale, whole galaxies are collecting matter on a 10 kpc scale.