Lyα COOLING RADIATION FROM HIGH-REDSHIFT HALOS

摘要

The baryons inside high-redshift halos with virial temperatures T ≈＞ 10~4 K cool radiatively as they condense inside dark matter potential wells. We show that the release of the gravitational binding energy, over the halo assembly timescale, results in a significant and detectable Lyα flux. At the limiting line flux ≈10~-19 ergs s~-1 cm~-2 arcsec~-2 of the Next Generation Space Telescope, several sufficiently massive halos, with velocity dispersions σ≈＞120 km s~-1, would be visible per 4'× 4' field. The halos would have characteristic angular sizes of ≈10", would be detectable in a broadband survey out to z ≈ 6-8, and would provide a direct probe of galaxies in the process of forming. They may be accompanied by He~+ Lyα emission at the ≈10/100 level, but remain undetectable at other wavelengths. Our predictions are in good agreement with the recent finding of two Lyα “blobs” at z = 3.1 by Steidel et al.