Genevieve Graves, of UC Santa Cruz


"The two-dimensional family of galaxy star formation histories"


To zeroth order, galaxies are a one-parameter family in which all 
properties scale with mass.  Manifestations of this 1D family include the
color-magnitude, mass-metallicity, and black hole mass-sigma relations. 
With so many mass-dependent galaxy properties, it is difficult to 
determine those properties that are critically linked to galaxy evolution.
I show that the star formation histories of early type galaxies in fact 
form a two-dimensional family, and that these two dimensions correspond to
differences in the structural properties of galaxies --- they can be
mapped onto a cross-section through the Fundamental Plane.  The first
dimension of this space scales most closely with galaxy velocity 
dispersion (not luminosity, stellar mass, or dynamical mass).  The 
second is correlated with differences in galaxy surface brightnesses and 
surface mass densities at fixed total mass.  This second dimension of 
variation may make it possible to identify the physical properties that 
determine galaxy star formation histories