The Size Evolution of Galaxies since z~3: Combining SDSS, GEMS, and FIRES

We present the evolution of the luminosity-size and stellar mass-size relations of luminous (LV ≳ 3.4 × 1010 h L☉) and massive (M* ≳ 3 × 1010 h M☉) galaxies in the last ~11 Gyr. We use very deep near-infrared images of the Hubble Deep Field-South and the MS 1054-03 field in the Js, H, and Ks bands from FIRES to retrieve the sizes in the optical rest frame for galaxies with z > 1. We combine our results with those from GEMS at 0.2 < z < 1 and SDSS at z ~ 0.1 to achieve a comprehensive picture of the optical rest-frame size evolution from z = 0 to 3. Galaxies are differentiated according to their light concentration using the Sérsic index n. For less concentrated objects, the galaxies at a given luminosity were typically ~3 ± 0.5 (±2 σ) times smaller at z ~ 2.5 than those we see today. The stellar mass-size relation has evolved less: the mean size at a given stellar mass was ~2 ± 0.5 times smaller at z ~ 2.5, evolving proportionally to (1 + z)-0.40±0.06. Simple scaling relations between dark matter halos and baryons in a hierarchical cosmogony predict a stronger (although consistent within the error bars) than observed evolution of the stellar mass-size relation. The observed luminosity-size evolution out to z ~ 2.5 matches well recent infall model predictions for Milky Way-type objects. For low-n galaxies, the evolution of the stellar mass-size relation would follow naturally if the individual galaxies grow inside out. For highly concentrated objects, the situation is as follows: at a given luminosity, these galaxies were ~2.7 ± 1.1 times smaller at z ~ 2.5 (or, put differently, were typically ~2.2 ± 0.7 mag brighter at a given size than they are today), and at a given stellar mass the size has evolved proportionally to (1 + z)-0.45±0.10.