A compact early-type galaxy at z=0.6 under a magnifying lens: evidence for inside-out growth

We use Keck laser guide star adaptive optics imaging and exploit the magnifying effects of strong gravitational lensing (the effective resolution is FWHM approximate to 200 pc) to investigate the sub-kpc scale of an intermediate-redshift (z = 0.63), massive early-type galaxy being lensed by a foreground early-type galaxy; we dub this class of strong gravitational lens systems EELs, i.e. early-type/early-type lenses. We find that the background source is massive (M-* = 10(10.9)M(circle dot)) and compact (r(e) = 1.1 kpc), and a two-component fit is required to model accurately the surface brightness distribution, including an extended low-surface-brightness component. This extended component may arise from the evolution of higher redshift 'red nuggets' or may already be in place at z similar to 2 but is unobservable due to cosmological surface brightness dimming.