Constraining the cosmic equation of state from old galaxies at high redshift

New limits on the cosmic equation of state are derived from age measurements of three recently reported old high-redshift galaxies (OHRG). The results are based on a flat Friedmann–Robertson–Walker (FRW) type cosmological model driven by non-relativistic matter plus a smooth component parametrized by its equation of state pxωρx (ω−1). The range of ω is strongly dependent on the matter density parameter. For ΩM∼0.3, as indicated from dynamical measurements, the age estimates of the OHRG restrict the cosmic parameter to ω−0.27. However, if ΩM is the one suggested by some studies of field galaxies, i.e., ΩM≃0.5, only a cosmological constant (ω=−1) may be compatible with these data.