H2Line Emission Associated with the Formation of the First Stars

Molecular hydrogen line radiation emitted in formation events offirst-generation stars are evaluated in a discussion of its detectability byfuture observational facilities. H_2 luminosity evolution from the onset ofprestellar collapse until the formation of a \sim 100 M_{\odot} protostar isfollowed. Calculations are extended not only to the early phase of the runawaycollapse but also to the later phase of accretion, whose observational featureshave not been studied before. Contrary to the runaway collapse phase, where thepure-rotational lines are always dominant, in the accretion phase rovibrationalline emission becomes prominent. The maximum luminosity is also attained in theaccretion phase for strong emission lines. The peak intensity of the strongestrovibrational line reaches \sim 10^{-29} (W/m^2), corresponding to the fluxdensity of 10^{-5} (\mu Jy), for a source at the typical redshift offirst-generation star formation, 1+z=20. Although the redshifted rovibrationalH_2 emission from such an epoch falls in the wavelength range of thenext-generation infrared satellite, Space Infrared Telescope for Cosmology andAstrophysics, for exceeding the detection threshold 10^7 such protostars arerequired to reach the maximum luminosity simultaneously in a pregalactic cloud.It is improbable that this condition is satisfied in a realistic scenario ofearly structure formation.Comment: 16 pages, 5 figures, accepted by PAS