Cosmology Seminar: Phil Hopkins, CfA/Harvard

Recent observations suggest that elliptical galaxies can be divided into two broad classes: those with central "cusps" in their surface brightness profiles, and those with central "cores." The "cusp" class dominates the population at intermediate and lower luminosities, where ellipticals are also observed to be much more dense than spiral galaxies of the same mass. This discrepancy has presented a long-standing challenge for the "merger hypothesis", that ellipticals formed from the merger of disk galaxies, and the formation of new stars in a dissipational starburst has generally been postulated as the means to reconcile the observations. By combining new generations of numerical simulations of gas-rich disk-disk mergers and observations of the nuclei of elliptical galaxies, it is possible to show that these "cusps" preserve a memory of the merger history of elliptical galaxies, and can be used to reconstruct the role of dissipation in the formation of ellipticals even after a Hubble time of subsequent evolution.