An emission signature of the final stages of reionization is expected

An emission signature of the final stages of reionization is expected

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An emission signature of the final stages of reionization is expected, which could help specify its redshift. Broad and asymmetric Lyman α emission is predicted from blank sky areas in all directions (Baltz et al. 1998 ApJL 493, L1), whose intensity depends largely on baryon density, with a wavelength determined by the recombination redshift. A sensitive search for this feature has used a large number of HST STIS spectra covering blank-sky regions (Windhorst et al. 2001, in Deep Fields ), yielding to date an intensity limit for this feature anywhere in the redshift range z =6-9 somewhat higher than typical predictions. Emission features may also be observable from the expanding H II regions around individual sources earlier in reionization. While the optical depth in the Lyman α transition will be enormous, some photons can be scattered far enough to the red wing of the line to escape. The situation is analogous to escape of Lyman α from a galactic wind, with the Hubble expansion playing the role of the wind's velocity field. Only the red wing matters, since photons scattered to the blue wing are promptly absorbed by foreground gas at a redshift for which the photons are close to the line center. Loeb & Rybicki (1999 ApJ 524, 527) have shown that we may hope to detect the halos of scattered light around very luminous objects at z ~10, particularly with JWST. We might be able to see the H II regions themselves around some objects in dense environments
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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An emission signature of the final stages of reionization is expected

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