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 (pₓ = \ω\ρₓ), 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 (\Ωₓ= 0.7, \ω < -0.6), we find a lower bound of zf \≥ 7.7, whereas in the extreme case of \ΛCDM model (\ω = -1) the limit is slightly smaller (zf \≥ 5.8). The case for open cold dark matter models (OCDM) has also been discussed. For \Ωₘ \ 0.3, the formation redshift is restricted by zf \≥ 18. As a general result, if \Ωₘ \≥ 0.37, these galaxies are not formed in FRW cosmologies with no dark energy since for all these cases zf \→ \∞.