.. _physics-hiiRegionEscapeFraction:

HII Regions Escape Fractions
============================

Class providing models of the escape fraction :math:`f_\mathrm{esc}` of hydrogen-ionizing (Lyman-continuum) photons from individual H**ii** regions---the fraction of photons produced by massive stars that escape the H**ii** region into the surrounding :term:`ISM` or :term:`IGM` rather than being absorbed by gas within the region. The escape fraction is returned as a function of H**ii** region age, reflecting the time evolution as stellar winds and supernovae clear channels through the surrounding gas.

**Default implementation:** ``hiiRegionEscapeFractionFixed``

Methods
-------

``escapeFraction`` → ``double precision``
   Returns the escape fraction for hydrogen-ionizing photons.

   * ``double precision, intent(in ) :: ageHIIRegion``

.. _physics-hiiRegionEscapeFractionFixed:

``hiiRegionEscapeFractionFixed``
--------------------------------

Computes the escape fraction of hydrogen ionizing photons from HII regions. A fixed escape fraction of :math:`f_\mathrm{esc}`\ ``[escapeFraction]`` is assumed for HII regions with ages less than :math:`\tau_\mathrm{limit}=`\ ``{ageLimit}``.

**(Default implementation)**

**Parameters**

* ``[escapeFraction]`` (real; default ``0.006d0``) — Escape fraction of ionizing photons from young HII regions.
* ``[ageLimit]`` (real; default ``0.03d0``) — The age beyond which all ionizing photons are assumed to escape from HII regions.