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 FRW type cosmological model driven by nonrelativistic matter plus a smooth component parametrized by its equation of state $p_{x} = \omega\rho_{x}$ ($\omega \geq -1$). The range of $\omega$ is strongly dependent on the matter density parameter. For $\Omega_{M} \sim 0.3$, as indicated from dynamical measurements, the age estimates of the OHRG restricts the cosmic parameter to $\omega\leq - 0.27$. However, if $\Omega_{M}$ is the one suggested by some studies of field galaxies, i.e, $\Omega_{M} \simeq 0.5$, only a cosmological constant ($\omega=-1$) may be compatible with these data. 
J. A. S. Lima (UFRN-Brazil) and J. S. Alcaniz (UFRN-Brazil)