What Shapes a Galaxy? – The Relative Role of Mass and Environment in Forming Galactic Structure
Witnessing Disc Galaxy Evolution Through The Eyes of their Stellar Structures
Asa F. L. Bluck
University of Victoria
I will present new results from an extensive GIM2D bulge + disk morphological decomposition of over half a million SDSS galaxies, with log(M*/Msun) = 8 – 12 at z = 0.02 – 0.2. Bulge-to-total light distributions are constructed in each of the Sloan ugriz wavebands, and are then converted to stellar masses of the component bulges and disks via model SED fitting. For the first time we show the relationship between bulge-to-total stellar mass ratio (B/T) and stellar mass (M*) over four orders of magnitude. We find that central and satellite galaxies have a very similar B/T – M* relationship, which starts at low masses with a shallow gradient and then becomes significantly steeper at log(M*/Msun) > 10. We also investigate the B/T structural dependence on group halo mass, group/cluster-centric distance, and local galaxy density. We find positive correlations with all of these metrics, but interestingly, once the dominant stellar mass trend is accounted for, we find that there are only weak structural dependencies remaining on local environment. The tight observed relationship between B/T and M* can be used as a powerful new constraint for semi-analytic and hydrodynamical cosmological simulations of galaxy evolution, as well as a solid z ~ 0 foundation for comparison to the morphologies of galaxies at higher redshifts. Finally, we argue that the integrated galaxy merger history may be the primary driver of evolution in galaxy structure, since this is more accurately traced with total stellar mass than with halo mass or other environmental metrics.


09:00 - 10:30