### Abstract

We show that numerical simulations of reionization that resolve the Lyman limit systems (and, thus, correctly count absorptions of ionizing photons) have converged to about a 10% level for 5 < z < 6.2 and are in reasonable agreement (within 10%) with the SDSS data in this redshift interval. The SDSS data thus constrain the redshift of overlap of cosmic H II regions to z _{OVL} = 6.1 ± 0.15. At higher redshifts, the simulations are far from convergence on the mean Gunn-Peterson optical depth but achieve good convergence for the mean neutral hydrogen fraction. The simulations that fit the SDSS data, however, do not have nearly enough resolution to resolve the earliest episodes of star formation and are very far from converging on the precise value of the optical depth to Thomson scattering - any value between 6% and 10% is possible, depending on the convergence rate of the simulations and the fractional contribution of Population III stars. This is generally consistent with the third-year WMAP results, but much higher resolution simulations are required to come up with the sufficiently precise value for the Thomson optical depth that can be statistically compared with the WMAP data.

Original language | English (US) |
---|---|

Pages (from-to) | 1-6 |

Number of pages | 6 |

Journal | Astrophysical Journal |

Volume | 648 |

Issue number | 1 I |

DOIs | |

State | Published - Sep 1 2006 |

### Fingerprint

### Keywords

- Cosmology: theory
- Galaxies: formation
- Intergalactic medium
- Large-scale structure of universe

### ASJC Scopus subject areas

- Space and Planetary Science

### Cite this

*Astrophysical Journal*,

*648*(1 I), 1-6. https://doi.org/10.1086/505790

**Cosmic reionization redux.** / Gnedin, Nickolay Y.; Fan, Xiaohui.

Research output: Contribution to journal › Article

*Astrophysical Journal*, vol. 648, no. 1 I, pp. 1-6. https://doi.org/10.1086/505790

}

TY - JOUR

T1 - Cosmic reionization redux

AU - Gnedin, Nickolay Y.

AU - Fan, Xiaohui

PY - 2006/9/1

Y1 - 2006/9/1

N2 - We show that numerical simulations of reionization that resolve the Lyman limit systems (and, thus, correctly count absorptions of ionizing photons) have converged to about a 10% level for 5 < z < 6.2 and are in reasonable agreement (within 10%) with the SDSS data in this redshift interval. The SDSS data thus constrain the redshift of overlap of cosmic H II regions to z OVL = 6.1 ± 0.15. At higher redshifts, the simulations are far from convergence on the mean Gunn-Peterson optical depth but achieve good convergence for the mean neutral hydrogen fraction. The simulations that fit the SDSS data, however, do not have nearly enough resolution to resolve the earliest episodes of star formation and are very far from converging on the precise value of the optical depth to Thomson scattering - any value between 6% and 10% is possible, depending on the convergence rate of the simulations and the fractional contribution of Population III stars. This is generally consistent with the third-year WMAP results, but much higher resolution simulations are required to come up with the sufficiently precise value for the Thomson optical depth that can be statistically compared with the WMAP data.

AB - We show that numerical simulations of reionization that resolve the Lyman limit systems (and, thus, correctly count absorptions of ionizing photons) have converged to about a 10% level for 5 < z < 6.2 and are in reasonable agreement (within 10%) with the SDSS data in this redshift interval. The SDSS data thus constrain the redshift of overlap of cosmic H II regions to z OVL = 6.1 ± 0.15. At higher redshifts, the simulations are far from convergence on the mean Gunn-Peterson optical depth but achieve good convergence for the mean neutral hydrogen fraction. The simulations that fit the SDSS data, however, do not have nearly enough resolution to resolve the earliest episodes of star formation and are very far from converging on the precise value of the optical depth to Thomson scattering - any value between 6% and 10% is possible, depending on the convergence rate of the simulations and the fractional contribution of Population III stars. This is generally consistent with the third-year WMAP results, but much higher resolution simulations are required to come up with the sufficiently precise value for the Thomson optical depth that can be statistically compared with the WMAP data.

KW - Cosmology: theory

KW - Galaxies: formation

KW - Intergalactic medium

KW - Large-scale structure of universe

UR - http://www.scopus.com/inward/record.url?scp=33748807737&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33748807737&partnerID=8YFLogxK

U2 - 10.1086/505790

DO - 10.1086/505790

M3 - Article

AN - SCOPUS:33748807737

VL - 648

SP - 1

EP - 6

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 I

ER -