Next Contents Previous

1.6. Clues from the formation of a weak radio galaxy

After reviewing some of the specific discoveries by HST on galaxy evolution (Section 2) and galaxy formation through sub-galactic clumps (Section 3), it will be instructive to review the formation and evolution of a specific high redshift (weak radio) galaxy (Section 4). Radio galaxies have played an important role in the study of galaxy evolution, since these were for a long time the only galaxies that could be identified easily at high redshifts. Jet-induced star formation or non-thermal radiation scattered in a reflection cone are the most probable radiation processes in ultraluminous high redshift 3CR and 1 Jy radio galaxies (C90, M93, B97). It is not clear that these processes are universal, and their role needs to be clarified at high resolution for ~ 30-100 x weaker radio galaxies (for alpha1.410.178 gtapprox 1.2), which may be more representative of what ordinary young galaxies would look like at those redshifts. To test these conjectures, deep multicolor high-resolution HST/PC images (at 0".0455 pixels) were obtained of the faint, compact, radio galaxy LBDS 53W002, which has narrow emission lines at z = 2.390 (W91). Its line ratios suggest a weak Seyfert-like AGN, and constrain its non-stellar component to ~ 35±15% of its total rest-frame UV-continuum (W91; W92). Ground-based and pre-refurbished HST continuum images (W92) showed some alignment with the radio source axis on 0".5-1".0 scales (4.5-9 kpc), which itself is aligned with the much larger ground-based Lyalpha cloud (~ 25 x 45 kpc; W91). The PC images were obtained to constrain the relative contributions from 53W002's AGN and its young stellar population, and to examine the relations between these components and its dynamics during the galaxy collapse - whether this occurred as a global halo collapse (cf. ELS62), through the rapid merging of many sub-galactic sized objects (e.g., SZ78, P96b), through jet-induced star-formation (e.g., C90), or some combination thereof.