How big were the first cosmological objects?

We calculate the cooling times at constant density for haloes with virial temperatures from 100 K to 1 × 105 K that originate from a 3σfluctuation of a CDM power spectrum in three different cosmologies. Our intention is to determine the first objects that can cool to low temperatures, but not to follow their dynamical evolution. We identify two generations of haloes: those with low virial temperatures, Tvir ≲ 9000 K that remain largely neutral, …