Role of the H_2^+ channel in the primordial star formation under strong radiation field and the critical intensity for the supermassive star formation
Date Issued
2016
Author(s)
Abstract
We investigate the role of the H2+ channel on H2 molecule formation during the collapse of primordial gas clouds immersed in strong radiation fields which are assumed to have the shape of a diluted blackbody spectra with temperature Trad. Since the photodissociation rate of H2+ depends on its level population, we take full account of the vibrationally resolved H2+ kinetics. We find that in clouds under soft but intense radiation fields with spectral temperature Trad ≲ 7000 K, the H2+ channel is the dominant H2 formation process. On the other hand, for harder spectra with Trad ≳ 7000 K, the H- channel takes over H2+ in the production of molecular hydrogen. We calculate the critical radiation intensity needed for supermassive star formation by direct collapse and examine its dependence on the H2+ level population. Under the assumption of local thermodynamic equilibrium (LTE) level population, the critical intensity is underestimated by a factor of a few for soft spectra with Trad ≲ 7000 K. For harder spectra, the value of the critical intensity is not affected by the level population of H2+. This result justifies previous estimates of the critical intensity assuming LTE populations since radiation sources like young and/or metal-poor galaxies are predicted to have rather hard spectra.
Volume
456
Issue
1
Start page
270
Issn Identifier
0035-8711
Ads BibCode
2016MNRAS.456..270S
Rights
open.access
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