Size and velocity dispersion evolution of red and dead galaxies

Galaxies evolve from bright, blue spiral systems with lots of star-formation to faint, red elliptical systems housing long-lived stars. I studied, what are believed to be the ancestors of today's elliptical galaxies, red galaxies that existed when the Universe was only half as old as it is today. Although these red galaxies have similar masses as their counterparts today, they are much smaller. To understand the extreme size evolution they have undergone, I studied the dynamics of the stars in the galaxies using the world's largest optical telescope. Little evolution was found in the dynamics of the stars. This provided crucial evidence supporting the theory that red galaxies grow in size by cannibalising small systems in the outskirts of the galaxies. This way they grow in size without assembling large amounts of mass.