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Intergalactic H_2 Photodissociation and the Soft UV Background Produced by Population III Objects

Benedetta Ciardi·Andrea Ferrara·Tom Abel
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Abstract

We study the effects of the ionizing and dissociating photons produced by PopIII objects on the surrounding intergalactic medium. We find that the typical size of a H_2 photodissociated region, R_d ~ 1-5 kpc, is smaller than the mean distance between sources at z ~ 20-30, but larger than the ionized region by a factor depending on the detailed properties of the emission spectrum. This implies that clearing of intergalactic H_2 occurs before reionization of the universe is complete. In the same redshift range, the soft-UV background in the Lyman-Werner bands, when the intergalactic H and H_2 opacity is included, is found to be J_LW ~ 1d-30 - 1d-27 erg cm^{-2} s^{-1} Hz^{-1}. This value is well below the threshold required for the negative feedback of PopIII objects on the subsequent galaxy formation to be effective in that redshift range.

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Benedetta Ciardi, Andrea Ferrara, Tom Abel. 1999-04-09. Intergalactic H_2 Photodissociation and the Soft UV Background Produced by Population III Objects. https://arxiv.org/abs/astro-ph/9811137

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