.. _physics-hiiRegionMassFunction:

HII region mass functions
=========================

Class providing models of the H**ii** region mass function---the distribution of gas masses among star-forming regions within a galaxy. Methods return the cumulative distribution (fraction of H**ii** regions by count) and cumulative mass (fraction of H**ii** region gas by mass) between specified minimum and maximum masses. These distributions are used to model the emission-line properties and the interstellar medium structure of star-forming galaxies in on-the-fly output analysis.

**Default implementation:** ``hiiRegionMassFunctionRosolowsky2021``

Methods
-------

``cumulativeDistributionFunction`` → ``double precision``
   Returns the cumulative distribution of the HII region mass function between a minimum and maximum mass.

   * ``double precision, intent(in ) :: massMinimum, massMaximum``

``cumulativeMass`` → ``double precision``
   Returns the cumulative mass from the HII region mass function between a minimum and maximum mass.

   * ``double precision, intent(in ) :: massMinimum, massMaximum``

.. _physics-hiiRegionMassFunctionRosolowsky2021:

``hiiRegionMassFunctionRosolowsky2021``
---------------------------------------

An HII region stellar mass function class in which giant molecular clouds are assumed to turn a fixed fraction :math:`\epsilon=`\ ``[epsilon]`` of their mass into stars, and the giant molecular cloud mass function is given by :cite:t:`rosolowsky_giant_2021`:

.. math::

   \phi(M) \propto \left(\frac{m}{M}\right)^{\alpha} \exp\!\left(-\frac{m}{M}\right),

where :math:`M` is the mass of giant molecular cloud, :math:`M_\mathrm{min}=`\ ``[massMinimum]`` and :math:`M_\mathrm{max}=`\ ``[massMaximum]`` and the minimum and maximum giant molecular cloud masses respectively, and :math:`\alpha=`\ ``[exponent]``.

**(Default implementation)**

**Parameters**

* ``[epsilon]`` (default ``3.0d-2``) — Fraction of giant molecular cloud mass turned into stars.
* ``[exponent]`` (default ``-1.2d0``) — Exponent of the differential mass function.
* ``[massMinimum]`` (default ``1.0d4``) — Minimum mass of giant molecular clouds.
* ``[massMaximum]`` (default ``1.0d8``) — Maximum mass ofgiant molecular clouds.
* ``[massCutOff]`` (default ``4.7d6``) — Cut off mass of giant molecular clouds.