.. _secPPIC:


Preparing the photon packets initial condition file
###################################################

Three stand-alone codes are currently available to generate PPIC files
for different sources (see main paper for more details):

* a code to spawn photon packets from star particles, taking into
  account their ages and metallicites and using various SED libraries,
  ``PhotonsFromStars``
* a code to spawn Lyman−α photons emitted by the gas, taking into
  account both recombination and collisional contributions, ``LyaPhotonsFromGas``
* a simple code to produce ad-hoc sources which may be used for tests
  or idealised models, ``PhotonsFromSourceModel``

Emission from stars
-------------------

The first stand-alone code, ``PhotonsFromStars``, generates photon
packets from star particles which represent stellar populations of
single ages and metallicities. It has a number of options, set in the
parameter file below. 

.. code-block:: fortran

	!--------------------------------------------------------------------------------
	[PhotonsFromStars]
	# input / output parameters
	repository = directory_where_ramses_outputs_are
	snapnum    = output_number
	outputfile = path_to_the_photonsIC_file
	
	# computational domain parameters
	star_dom_type      = sphere
	star_dom_pos       = 5.000E-01 5.000E-01 5.000E-01
	star_dom_rsp       = 3.000E-02
	#  star_dom_size      = 3.000E-01
	#  star_dom_rin       = 0.000E+00
	#  star_dom_rout      = 3.000E-01
	#  star_dom_thickness = 1.000E-01
	
	# Particle weights 
	weight_type        = Mono
	weight_input_file  = path_to_the_table_file_with_SSP_weights
	
	# Spectral shape 
	spec_type               = Gauss
	spec_gauss_sigma_kms    = 20.0
	#  spec_powlaw_lmin_Ang    = 1.120E+03 ! [A]
	#  spec_powlaw_lmax_Ang    = 1.320E+03 ! [A]
	
	# miscelaneous parameters
	nPhotonPackets  = 1000000
	ranseed         = -100
	verbose         = T
	!--------------------------------------------------------------------------------
	
	!--------------------------------------------------------------------------------
	[ramses]
	self_shielding   = F
	ramses_rt        = F
	verbose          = T
	cosmo            = T
	use_initial_mass = F
	use_proper_time  = F
	itemp  = 5
	imetal = 6
	ihii   = 7
	iheii  = 8
	iheiii = 9
	!--------------------------------------------------------------------------------

Again, this should be compiled in rascas/f90 with ``make PhotonsFromStars`` and run with ``./PhotonsFromStars params_PFS.cfg``. 


Lyman−α emission from gas
-------------------------

The second stand-alone code, ``LyaPhotonsFromGas``, generates photon
packets which describe Lyman−α emission from the gas. 


Ad hoc source models
--------------------

The simplicity of PPIC files makes it straightforward to write these
files with any idealised configuration. An example is the code
``PhotonsFromSourceModel``, which can be used as it is or extended to
different configurations.