.. _physics-satelliteOrphanDistribution:

Satellite Orphan Distributions
==============================

Class providing distributions for orphan satellites---galaxies whose host dark matter subhalo has been disrupted or fallen below the mass resolution limit, so they no longer have an explicit subhalo tracked in the merger tree. Since orphans retain stellar mass and continue to orbit, their positions and velocities must be modelled statistically. Implementations return the spatial extent of the orphan distribution, and sample physical positions and peculiar velocities for individual orphan satellites, typically by assuming they trace the dark matter distribution or follow their last-known orbit.

**Default implementation:** ``satelliteOrphanDistributionTraceDarkMatter``

Methods
-------

``extent`` → ``double precision``
   The maximum extent of the distribution, i.e. the radius of a sphere centered on the host halo which encompasses all orphan satellites.

   * ``type(treeNode), intent(inout) :: node``

``position`` → ``double precision, dimension(3)``
   Return the position of the given orphan in physical coordinates.

   * ``type(treeNode), intent(inout) :: node``

``velocity`` → ``double precision, dimension(3)``
   Return the peculiar velocity of the given orphan in physical coordinates.

   * ``type(treeNode), intent(inout) :: node``

.. _physics-satelliteOrphanDistributionRandomIsotropic:

``satelliteOrphanDistributionRandomIsotropic``
----------------------------------------------

An abstract orphan satellite distribution which assumes an isotropic, random distribution of positions, and velocities drawn from an isotropic normal distribution. The radial distribution and velocity dispersion must be specified by the child class.

**Methods**

* ``inverseCumulativeMassFunctionRadial`` — Return the radius enclosing the given fraction of the orphan satellite population.
* ``velocityDispersion`` — Return the 1-D velocity dispersion of the orphan satellite population.
* ``initialize`` — Initialize the class.

.. _physics-satelliteOrphanDistributionTraceDarkMatter:

``satelliteOrphanDistributionTraceDarkMatter``
----------------------------------------------

An orphan satellite distribution which assumes an isotropic, random distribution with orphans tracing the radial distribution of dark matter.

**(Default implementation)**

**Methods**

* ``assignPosition`` — Assign a position to a node such that it traces the dark matter of its host.