The Luminosity‐Size and Mass‐Size Relations of Galaxies out to z ∼ 3

Abstract

The luminosity-size and mass-size distributions of galaxies out to z ∼ 3 are presented. We use very deep near-infrared images of the Hubble Deep Field-South in the Js, H, and Ks bands, taken as part of FIRES at the VLT, to follow the evolution of the optical rest-frame sizes of galaxies. For a total of 168 galaxies with Ks,AB ≤ 23.5, we find that the rest-frame V-band sizes re,V of luminous galaxies (〈LV〉 ∼ 2 × 1010 h-2 L ⊙) at 2 < z < 3 are 3 times smaller than for equally luminous galaxies today. In contrast, the mass-size relation has evolved relatively little: the size at mass 〈M*〉 ∼ 2 × 1010 h-2 M⊙ has changed by 20% (±20%) since z ∼ 2.5. Both results can be reconciled by the fact that the stellar M/L ratio is lower in the luminous high-z galaxies than in nearby ones because they have young stellar populations. The lower incidence of large galaxies at z ∼ 3 seems to reflect the rarity of galaxies with high stellar mass.