Hydrogen molecules in quasar broad-line regions

Details Hydrogen molecules in quasar broad-line regions Hydrogen molecules in quasar broad-line regions

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993mnras.262..359c&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 262, no. 2, p. 359-368.

Astronomy and Astrophysics

Astronomy

5

Hydrogen, Interstellar Chemistry, Interstellar Matter, Molecular Clouds, Quasars, Astronomical Models, Cosmic Dust, Radiative Transfer

Scientific paper

We reconsider the question of molecule formation deep within quasar broad-line region (BLR) clouds. Earlier work ignored the rapid photodetachment of H(-) by the intense radiation flux between 0.75 and 13.6 eV. The negative hydrogen ion participates in the H2 formation pathway that is most important in the BLR environment, and our calculations reveal an order-of-magnitude decrease in the H2 abundance at large optical depths when the photodetachment process is considered. We first explore the contribution of collisions between excited and ground-state atomic hydrogen to molecule formation, because Lyman-line trapping greatly enhances the excited-state populations. Neither radiative association nor associative ionization yields a significant enhancement of the total H2 abundance in the neutral zone. The likely importance of small amounts of dust is then explored. The H-to-H2 conversion again can be essentially completed at gas column densities of about 10 exp 23/sq cm, if a dust-to-gas abundance only 1/10 of that characteristic of our Galaxy's interstellar matter exists in BLR clouds.

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