Department of Astronomy


The formation and evolution of massive compact galaxies


Mauro Giavalisco

University of Massachusetts


Compact and massive galaxies at high redshift, especially those that have stopped forming stars, offer the opportunity to test some of our key ideas on galaxy evolution. These are the first galaxies in the universe to quench star formation, and their large stellar mass and extreme stellar density strongly suggest that they assembled the bulk of their stellar mass formed through a highly dissipative gaseous mechanism, with hierarchical merging of pre-existing galaxies being comparatively unimportant. We identified likely progenitors when they were still star forming at redshift z>3 and found evidence that their stellar populations are on average older than other non-compact star-forming galaxies of similar mass at the same epoch, indicative of an accelerated evolution. They also seem to have more energetic feedback in the form of faster and more turbulent outflows. While compact galaxies dominated the population of passive and massive galaxies at high redshift, after reaching a peak of abundance at redshift around 1, they are much rarer in the local universe. By looking at the differential evolution of these structures in environment of different densities, such as groups and clusters spanning a range of richness and mass it should be possible to identify the evolutionary meachanisms that might have led to their disappearance, as well as to the formation of modern early type galaxies.