Deep Hubble Space Telescope imaging of a compact radio galaxy at z = 2.390

We present deep 4 hr HST/WFC images in V and I of the LBDS radio galaxy 53W002, a weak and compact narrow-line galaxy recently discovered at z = 2.390. After deconvolution, the resolution is 0″.2 FWHM. Its I-band structure is quite compact with 30% ± 10% of its flux in the central ≲ 1 kpc, presumably from its AGN. This is surrounded by a clearly extended and rather symmetric envelope with effective radius ∼1″.1 (4-15 kpc for H₀ = 50-100, q₀ = 0-0.5). In V, 53W002 is somewhat elongated at the same sky PA as its Lyα cloud and its VLA radio axis. We compare 52W002's rest-frame UV profile to a properly rescaled image of a nearby early-type galaxy. The much younger starburst in 53W002 has 10-20 times higher central UV surface brightness, but otherwise an r^1/4-like light profile consistent with that of nearby luminous early-type galaxies. The available data are consistent with 53W002 being a genuinely young galaxy that only started forming stars ≲0.5 Gyr before z = 2.390, but has nonetheless (just) managed to develop a rather regular light profile at z = 2.390, and suggest that the dynamical collapse of this galaxy started at about the same time as its first major burst of star formation. For this galaxy, both ∼0.5 Gyr time scales are consistent with z_form = 2.7-4.2 (for H₀ = 50-100, q₀ = 0-0.5).