Feedback regulated star formation in galaxies evolving from bursty clumps to time-steady discs

How star formation rates are regulated in disk galaxies is a key question in galaxy evolution. Feedback regulated models of star formation posit that star forming disks are governed by vertical equilibrium between gravity and pressure from stellar feedback and predict Kennicutt-Schmidt (KS)-like relations. We use the FIRE hydrodynamic cosmological zoom-in simulations, which include multi-channel models for stellar feedback and produce a complex and multiphase ISM, to show that vertical pressure balance in Milky Way-mass star forming disk galaxies leads to time-steady and spatially distributed star formation, reproducing the KS-relation at low redshift. However, the simulations also predict that at high redshift these galaxies have clumpy morphologies and time-variables or "bursty" star formation rates. We discuss the implications of these complex star formation histories on the time-scales probed by commonly used observational star formation rate indicators (FU V and H-alpha)