Andrey Kravtsov - March 9, 2018

How galaxies form stars

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.