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We investigate observational constraints on the cosmic equation of state from measurements of angular size for a large sample of milliarcsecond compact radio-sources. The results are based on a flat Friedmann-Robertson-Walker (FRW) type models driven by non-relativistic matter plus a smooth dark energy component parametrized by its equation of state pₓ = \ \ₓ (-1 \ \ < 0). The allowed intervals for \ and \_ are heavily dependent on the value of the mean projected linear size l. For l \ 20h^-1 - 30h^-1 pc, we find \_ \ 0. 62, \ \ -0. 2 and \_ \ 0. 17, \ \ -0. 65 (68% c. l. ), respectively. As a general result, this analysis shows that if one minimizes \^2 for the parameters l, \_ and \, the conventional flat \CDM model (\ = -1) with \_ = 0. 22 and l = 22. 6 h^-1pc is the best fit for these angular size data.
Lima et al. (Sun,) studied this question.