### Abstract

We investigate the relation between the turbulent Mach number (M) and the escape fraction of Lyman continuum photons ( f_{esc}) in high-redshift galaxies. Approximating the turbulence as isothermal and isotropic, we show that the increase in the variance in column densities from M = 1 to M = 10 causes f_{esc} to increase by ≈25%, and the increase from M = 1 to M = 20 causes f_{esc} to increases by ≈50% for a medium with opacity t = 1. At a fixed Mach number, the correction factor for escape fraction relative to a constant column density case scales exponentially with the opacity in the cell, which has a large impact for simulated star-forming regions. Furthermore, in simulations of isotropic turbulence with full atomic/ionic cooling and chemistry, the fraction of HI drops by a factor of ≈2.5 at M ≈ 10 even when the mean temperature is ≈ 5 × 10^{3} K. If turbulence is unresolved, these effects together enhance f_{esc} by a factor > 3 at Mach numbers above 10. Such Mach numbers are common at high redshifts where vigorous turbulence is driven by supernovae, gravitational instabilities, and merger activity, as shown both by numerical simulations and observations. These results, if implemented in the current hydrodynamical cosmological simulations to account for unresolved turbulence, can boost the theoretical predictions of the Lyman Continuum photon escape fraction and further constrain the sources of reionization.

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

Article number | L9 |

Journal | Astrophysical Journal Letters |

Volume | 832 |

Issue number | 1 |

DOIs | |

State | Published - Nov 20 2016 |

### Keywords

- galaxies: ISM
- galaxies: high-redshift
- radiative transfer
- turbulence

### ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science