The epoch of structure formation in blue mixed dark matter models

Abstract

Recent data on the high-redshift abundance of damped Lyα systems are compared with theoretical predictions for ‘blue’ (i.e. n> 1) mixed dark matter (MDM) models. The results show that decreasing the hot component fraction Ωv and/or increasing the primordial spectral index n leads to an earlier epoch of cosmic structure formation. We also show, however, that varying Ωv and n in these ways makes the models barely consistent with the observed abundance of galaxy clusters. Therefore, requiring both the observational constraints on damped Lya systems and the cluster abundance to be satisfied simultaneously represents a challenge for the MDM class of models.