added Rockstar information

docs/source/halos.rst

@@ -3,6 +3,11 @@
 Halo catalogues
 ===============
 
+Quijote contains FoF and Rockstar halo catalogs.
+
+FoF
+~~~
+
 The FoF halo catalogs can be read through the `readfof.py <https://github.com/franciscovillaescusa/Pylians3/blob/master/library/readfof.py>`_ script. If you have `Pylians <https://github.com/franciscovillaescusa/Pylians3>`_ installed you already have it. An example on how to read a halo catalog is this (we provide further details on how to read and manipulate these catalogs in :ref:`tutorials`):
 
 .. code-block:: python
@@ -34,3 +39,40 @@ The number in the name of the halo catalogue represents its redshift:
 - 002 ------> z=1
 - 003 ------> z=0.5
 - 004 ------> z=0
+
+.. Note::
+
+   The above correspondence applies to the majority of the simulations but not to all of them. For instance, for Quijote-ODD, 000 represents redshift 1 while 001 corresponds to redshift 0. Thus, we always recommend reading the redshift of the correspond snapshot.
+
+
+Rockstar
+~~~~~~~~
+
+Quijote also contain Rockstar halo catalogs. A typical Rockstar folder will contain the following files:
+
+- ``out_X.list``. These are the Rockstar-generated halo+subhalo catalogs. X usually goes from 0 to 4, and it represents the snapshot number. E.g. the rockstar catalog corresponding to the snapdir_004 would be out_4.list. Those are ASCII files where the header describes the content of the file.
+- ``out_X_pid.list``. These are the Rockstar-generated halo+subhalo catalogs. X usually goes from 0 to 4, and it represents the snapshot number. E.g. the rockstar catalog corresponding to the snapdir_004 would be out_4.list. Those are ASCII files where the header describes the content of the file. The main difference between these files and the ``out_X.list`` is that ``out_X_pid.list`` contains an additional column called PID that allow to distinguish between halos and halos. For halos :math:`{\rm PID}=-1` while for subhalos PID is the parent halo ID.
+- ``rockstar_params.cfg``. This file contains the Rockstar parameter file.
+- ``rockstar.slurm``. This file contains the slurm submission script used to run Rockstar.
+- ``rockstar.slurm``. This file contains the output from the slurm script.
+- ``rockstar.cfg``. The Rockstar-generated configuration file. This is generated by Rockstar when running it.
+- ``output.dat``. The output generated by Rockstar when running it.
+
+In general, we recommend using the ``out_X_pid.list`` files that can be read easily with something like this:
+
+.. code-block:: python
+
+   import numpy as np
+
+   # catalog file
+   f_catalog = '/home/fvillaescusa/Quijote/Halos/fiducial/0/out_4_pid.list'
+   
+   # read the halo catalog
+   data = np.loadtxt('f_catalog')
+
+   # we can now get the different properties of the halos
+   Mvir = data[:,2]
+   Vmax = data[:,3]
+   PID  = data[:,41] 
+   
+