Title:
Role of the H_2^+ channel in the primordial star formation under strong radiation field and the critical intensity for the supermassive star formation
Authors:
Sugimura, K.; Coppola, C. M.; Omukai, K.; Galli, D.; Palla, F.
Affiliation:
AA(Astronomical Institute, Tohoku University, Aoba, Sendai 980-8578, Japan sugimura@astr.tohoku.ac.jp), AB(Dipartimento di Chimica, Università degli Studi di Bari, Via Orabona 4, I-70126 Bari, Italy; INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy), AC(Astronomical Institute, Tohoku University, Aoba, Sendai 980-8578, Japan), AD(INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy), AE(INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 456, Issue 1, p.270-277 (MNRAS Homepage)
Publication Date:
02/2016
Origin:
OUP
Astronomy Keywords:
molecular processes, quasars: supermassive black holes, cosmology: theory
Abstract Copyright:
2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:
10.1093/mnras/stv2655
Bibliographic Code:
2016MNRAS.456..270S
Abstract
We investigate the role of the H_2^+ 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 H_2^+ depends
on its level population, we take full account of the vibrationally resolved
H_2^+ kinetics. We find that in clouds under soft but intense radiation fields
with spectral temperature Trad ? 7000 K, the H_2^+ channel is the
dominant H2 formation process. On the other hand, for harder spectra with
Trad ? 7000 K, the H- channel takes over H_2^+ 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 H_2^+ 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 H_2^+. 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.