Witnessing the Differential Evolution of Disk Galaxies in Luminosity and Size via Gravitational Lensing

We take advantage of the magnification in size and flux of a galaxy provided by gravitational lensing to analyze the properties of 62 strongly lensed galaxies from the Sloan Lens ACS (SLACS) Survey. The sample of lensed galaxies spans a redshift range of 0.20 ? z ? 1.20 with a median redshift of z = 0.61. We use the lens modeling code LENSFIT to derive the luminosities, sizes, and S?rsic indices of the lensed galaxies. The measured properties of the lensed galaxies show a primarily compact, disk-like population with the peaks of the size and S?rsic index distributions corresponding to ~1.50 kpc and n ~ 1, respectively. Comparison of the SLACS galaxies to a non-lensing, broadband imaging survey shows that a lensing survey allows us to probe a galaxy population that reaches ~2 mag fainter. Our analysis allows us to compare the z = 0.61 disk galaxy sample (n ? 2.5) to an unprecedented local galaxy sample of ~670, 000 SDSS galaxies at z ~ 0.1; this analysis indicates that the evolution of the luminosity-size relation since z ~ 1 may not be fully explained by a pure-size or pure-luminosity evolution but may instead require a combination of both. Our observations are also in agreement with recent numerical simulations of disk galaxies that show evidence of a mass-dependent evolution since z ~ 1, where high-mass disk galaxies (M > 109 M ?) evolve more in size and low-mass disk galaxies (M ? 109 M ?) evolve more in luminosity.