Dark Energy and the Epoch of Galaxy Formation

The influence of a dark component on the first epoch of galaxy formation isanalysed by using the ages of the three oldest high-redshift galaxies known inthe literature. Our results, based on a spatially flat accelerated Universedriven by a "quintessence" component ($p_x = \omega\rho_x$), show that if theinferred ages of these objects are correct the first formation era is pushedback 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 isslightly 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 formationredshift is restricted by $z_f \geq 18$. As a general result, if $\Omega_m \geq0.37$, these galaxies are not formed in FRW cosmologies with no dark energysince for all these cases $z_f \to \infty$.Comment: 17 pages, 3 figures, Accepted for publication in Astrophysical Journal Letter