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Observational constraints to a large class of decaying vacuum cosmologies are derived using the angular size data of compact radio sources and the latest age estimates of globular clusters. For this class of deflationary (t) models, the present value of the vacuum energy density is quantified by a positive parameter smaller than unity. In the case of milliarcsecond compact radio-sources, we find that the allowed intervals for and the matter density parameter ₌ are heavily dependent on the value of the mean projected linear size l. For l20h^-1-30h^-1 pc, the best fit occurs for 0. 58, ₌0. 58, and 0. 76, ₌0. 28, respectively. This analysis shows that if one minimizes ^2 for the free parameters l, ₌ and, the best fit for these angular size data corresponds to a decaying (t) with ₌=0. 54, =0. 6, and l=22. 64h^-1 pc. Constraints from age estimates of globular clusters and old high redshift galaxies are not so restrictive, thereby suggesting that there is no age crisis for this kind of (t) cosmologies.
Cunha et al. (Mon,) studied this question.