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

New limits on the cosmic equation of state are derived from age measurement s of three recently reported old high-redshift galaxies (OHRG). The results are based on a flat Friedmann-Robertson-Walker (FRW) type cosmological mod el driven by non-relativistic matter plus a smooth component parametrized b y its equation of state p(X) = omega rho(X) (omega greater than or equal to -1). The range of omega is strongly dependent on the matter density parame ter. For Omega(M) similar to 0.3, as indicated from dynamical measurements, the age estimates of the OHRG restrict the cosmic parameter to omega less than or equal to -0.27. However, if Omega(M) is the one suggested by some s tudies of field galaxies, i.e., Omega(M) similar or equal to 0.5, only a co smological constant (omega = -1) may be compatible with these data.