| Abstract: | The thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at certain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at z = 10 it increases sharply from about qT ～ 10–3 for dark halos of M = 5 × 107 M⊙ to ～ 0.1 for halos with M = 108 M⊙. Further increase of the halo mass does not lead however to a significant growth of qT – the asymptotic value for M ? 108 M⊙ is 0.3. We estimate the star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal‐poor low‐mass stars in the Milky Way may have been formed from primordial gas behind such shocks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
