Constraining Reionization with the Evolution of the Luminosity Function of Lyα Emitting Galaxies
Abstract
At redshifts beyond z>~6, as the mean fraction of neutral hydrogen <xHI> in the intergalactic medium (IGM) increases, the line flux of Lyα emitters can be significantly attenuated, which can result in a decrease in the observed number of emitters at a given Lyα flux. However, cosmological H II regions surrounding the Lyα emitting galaxies alleviate these effects. We use simple models of the Lyα line attenuation that incorporate the presence of H II regions to predict the overall effect of the Lyα absorption on the Lyα luminosity function (LF). We find, in agreement with other recent studies, that a fully neutral IGM is inconsistent with the Lyα LF remaining unchanged from z=5.7 to z=6.5, as suggested by recent observations. However, the presence of local H II regions prohibits placing a tight constraint on the mean neutral fraction. We find <xHI><~0.25 the presence of strong winds and/or the clustering of ionizing sources would further weaken this constraint. We conclude that the evolution of the Lyα LF is consistent with reionization occurring near this redshift, as suggested by other observations. Finally, we suggest that a measurement of observed Lyα line width as a function of the Lyα luminosity, in a future, larger sample of Lyα emitters, may serve as a robust diagnostic of the neutral fraction in the IGM.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2005
- DOI:
- 10.1086/428645
- arXiv:
- arXiv:astro-ph/0411038
- Bibcode:
- 2005ApJ...623..627H
- Keywords:
-
- Cosmology: Theory;
- Cosmology: Early Universe;
- Galaxies: Formation;
- Galaxies: High-Redshift;
- Galaxies: Quasars: Absorption Lines;
- Galaxies: Quasars: General;
- Astrophysics
- E-Print:
- 4 emulateapj pages, 4 figures, submitted to ApJ Letters