The luminosity-size and mass-size relations of galaxies out to z ∼ 3

The luminosity-size and mass-size distributions of galaxies out to z similar to 3 are presented. We use very deep near-infrared images of the Hubble Deep Field - South in the J(s), H, and K-s 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 K-s,K-AB less than or equal to 23.5, we find that the rest-frame V-band sizes r(e,V) of luminous galaxies [L-V] similar to2 x 10(10)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-*] similar to2 x 10(10) h(-2) M-. has changed by 20% ( +/- 20%) since z similar to 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 similar to 3 seems to reflect the rarity of galaxies with high stellar mass.