We present Hubble Space T elescope WFPC2 images taken through a broad red Ðlter (F702W) of 30 Third Cambridge Catalog compact steep spectrum (CSS) radio sources. We have overlaid radio maps taken from the literature on the optical images to determine the radio-optical alignment and to study detailed correspondence. All CSS sources for which the relative orientation between the optical and radio can be measured display good alignment between the optical and radio emission down to the lowest redshift in the sample, z D 0.1. The alignment e †ect does not occur at this relatively low redshift for the large-scale 3CR radio sources, which tend to show a signiÐcant alignment only at z [ 0.6, as shown by McCarthy et al., Chambers et al., and de Ko † et al. We Ðnd candidates for optical synchrotron hot spots in 3C 213.1 and 3C 380 and an optical jet in 3C 346.

Abstract. Using the final version of the VLA FIRST survey (Becker et al. 2003), the optical Sloan Digital Sky Survey Data Release 3 (DR3) quasar list and a series of carefully selected criteria, we have defined the largest homogeneous population of double-lobed sources. With the precise sample definition, the increased depth and sensitivity of the survey data, the large size of the dataset, and our self-consistent method of analysis, which addresses many of the problems associated with previous work in the area, we are able to: a) explore the correlations between the intrinsic properties of the double-lobed radio sources (the results are also confirmed by a non-parametric analysis) and study their evolution, b) place more interesting and tighter constraints on the cosmological parameters, distinguish among the different cosmology models, and determine the impact of the angular sizeredshift studies in cosmology, c) further our understanding of the behavior of the intergalactic medium (IGM) density as a function of redshift and shed more light to the quasar-radio galaxy unification issue.