High-redshift objects and the generalized Chaplygin gas

Motivated by recent developments in particle physics and cosmology, there has been growing interest in a unified description of dark matter and dark energy scenarios. In this paper we explore observational constraints from age estimates of high-z objects on cosmological models dominated by an exotic fluid with an equation of state p=-A/^ (the so-called generalized Chaplygin gas) which has the interesting feature of interpolating between nonrelativistic matter and negative-pressure dark energy regimes. As a general result we find that, if the age estimates of these objects are correct, they impose very restrictive limits on some of these scenarios.