time: December, 15th 2pm
speaker: Dr. Yong Shi (Caltech)
Place: Middle Conference Room
Abstract: Star forms from  interstellar medium.  The resulting stellar mass growth, chemical enrichment and energy feedback are key processes of galaxy formation  and evolution. While star forms  through a series of complicated processes  from  initial gas  collapse  to final  star formation, an empirical law between star formation rate (SFR) and gas offers critical  tests of  understandings of star  formation processes and have crucial  applications  to studies  of  galaxy formation  and evolution.  I will present our proposed  new  empirical relation  -- the extended Schmidt law, a  relationship between star formation efficiency (SFR/gas-mass)  and stellar  mass  surface density.　 Compared to  the classical Kennicutt-Schmidt  law, this new relation does  not break at the low density regime where the KS law does. Comparison with physical models of star formation shows that this relation can be reproduced by models  of gas free-fall  in  a  stellar-gravitational potential  and pressure-supported  star  formation.  By  applying  it  to the model of gas accretion and star formation in lambda CDM, I show that it  can re-produce the  observed main sequence of star-forming galaxies from  z=0 up z=2 without invoking ad hoc mechanisms to delay star formation in low mass galaxies.