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On the rapid demise of Ly α emitters at redshift z ≳ 7 due to the increasing incidence of optically thick absorption systems
- Source :
- Monthly Notices of the Royal Astronomical Society. 429:1695-1704
- Publication Year :
- 2012
- Publisher :
- Oxford University Press (OUP), 2012.
-
Abstract
- A variety of independent observational studies have now reported a significant decline in the fraction of Lyman-break galaxies which exhibit Ly-a emission over the redshift interval z=6-7. In combination with the strong damping wing extending redward of Ly-a in the spectrum of the bright z=7.085 quasar ULAS 1120+0641, this has strengthened suggestions that the hydrogen in the intergalactic medium (IGM) is still substantially neutral at z~7. Current theoretical models imply HI fractions as large as 40-90 per cent may be required to explain these data assuming there is no intrinsic evolution in the Ly-a emitter population. We propose that such large neutral fractions are not necessary. Based on a hydrodynamical simulation which reproduces the absorption spectra of high-redshift (z~6-7) quasars, we demonstrate that the opacity of the intervening IGM redward of rest-frame Ly-a can rise rapidly in average regions of the Universe simply because of the increasing incidence of absorption systems which are optically thick to Lyman continuum photons as the tail-end of reionisation is approached. Our simulations suggest these data do not require a large change in the IGM neutral fraction by several tens of per cent from z=6-7, but may instead be indicative of the rapid decrease in the typical mean free path for ionising photons expected during the final stages of reionisation.
Details
- ISSN :
- 13652966 and 00358711
- Volume :
- 429
- Database :
- OpenAIRE
- Journal :
- Monthly Notices of the Royal Astronomical Society
- Accession number :
- edsair.doi...........18f91cdc2ab3360438f60cd34b5488c5