Formation of stars in galaxies is a complex multi-scale process. Despite this complexity, the star formation rate (SFR) on kiloparsec- and larger scales in observed galaxies scales almost linearly with total gas mass: SFR=Mgas/tau, where tau is ~5-10 Gyrs for L* galaxies and exhibits a relatively small scatter. The value of tau was a long standing puzzle, because it is much longer than time scales of any relevant processes in the ISM. Many galaxy formation simulations could reproduce the observed value, but the physics controlling it was not well understood. Moreover, a number of recent simulations with strong stellar feedback showed that depletion time was nearly insensitive to the local efficiency of star formation in individual small-scale star-forming regions – a phenomenon described as “self-regulation.” I will present results of a suite of L* galaxy simulations that explore this behavior systematically and a simple physical model that explains the physics behind both the observed long gas depletion times in galaxies and results of recent numerical simulations.
Host: Mark Vogelsberger