Charles Steinhardt - Is the Stellar Initial Mass Function Truly Universal?

Current techniques for analyzing large photometric catalogs are generally forced to assume a single, universal stellar initial mass function (IMF), although the IMF should be expected to vary depending upon conditions within a star-forming galaxy.  The introduction of an additional parameter into photometric template fitting allows galaxies to be fit with a range of different IMFs.   Most galaxies are best fit with a bottom-lighter IMF than the Milky Way, and this change in IMF also modifies inferred properties such as stellar mass and star formation rate.  Several surprising new features appear, including significant constraints on the feedback mechanisms responsible for star formation and subsequent quenching.  Additionally, the same techniques might indicate that most galaxies go through an earliest phase of star formation dominated by different feedback mechanisms and centered in galactic cores prior to the more typical star formation at later times.