Dark energy and the epoch of galaxy formation

The influence of a dark component on the first epoch of galaxy formation is analysed by using the ages of the three oldest high-redshift galaxies known in the literature. Our results, based on a spatially flat accelerated Universe driven by a "quintessence" component ($p_x = \omega\rho_x$), show that if the inferred ages of these objects are correct the first formation era is pushed back to extremely high redshifts. For the present best-fit quintessence model ($\Omega_{x}= 0.7$, $\omega < -0.6$), we find a lower bound of $z_f \geq 7.7$, whereas in the extreme case of $\Lambda$CDM model ($\omega = -1$) the limit is slightly smaller ($z_f \geq 5.8$). The case for open cold dark matter models (OCDM) has also been discussed. For $\Omega_m \simeq 0.3$, the formation redshift is restricted by $z_f \geq 18$. As a general result, if $\Omega_m \geq 0.37$, these galaxies are not formed in FRW cosmologies with no dark energy since for all these cases $z_f \to \infty$.