Commit 36f69c1b authored by Matthieu Schaller's avatar Matthieu Schaller
Browse files

Added general description of the EAGLE cooling model to the RTD. YAML parameters still to be added.

parent 6e2ea0fc
......@@ -143,8 +143,55 @@ Whilst one would use the following values for solar abundances
Cooling: Wiersma+2008a
~~~~~~~~~~~~~~~~~~~~~~
Gas cooling: Wiersma+2009a
~~~~~~~~~~~~~~~~~~~~~~~~~~
The gas cooling is based on the redshift-dependent tables of `Wiersma et
al. (2009) <http://adsabs.harvard.edu/abs/2009MNRAS.393...99W>`_ that include
element-by-element cooling rates for the 11 elements (`H`, `He`, `C`, `N`, `O`,
`Ne`, `Mg`, `Si`, `S`, `Ca` and `Fe`) that dominate the total rates. The tables
assume that the gas is in ionization equilibrium with the cosmic microwave
background (CMB) as well as with the evolving X-ray and UV background from
galaxies and quasars described by the model of `Haardt & Madau (2001)
<http://adsabs.harvard.edu/abs/2001cghr.confE..64H>`_. Note that this model
ignores *local* sources of ionization, self-shielding and non-equilibrium
cooling/heating. The tables can be obtained from this `link
<http://virgodb.cosma.dur.ac.uk/swift-webstorage/CoolingTables/EAGLE/coolingtables.tar.gz>`_
which is a re-packaged version of the `original tables
<http://www.strw.leidenuniv.nl/WSS08/>`_
The Wiersma tables containing the cooling rates as a function of redshift,
Hydrogen number density, Helium fraction (:math:`X_{He} / (X_{He} + X_{H})`) and
element abundance relative to the solar abundance pattern assumed by the tables
(see equation 4 in the original paper). As the particles do not carry the mass
fraction of `S` and `Ca`, we compute the contribution to the cooling rate of
these elements from the abundance of `Si`. More specifically, we assume that
their abundance relative to the table's solar abundance pattern is the same as
the relative abundance of `Si`. Users can optionally modify the ratios used for
`S` and `Ca`.
Above the redshift of Hydrogen re-ionization we use the extra table containing
net cooling rates for gas exposed to the CMB and a UV + X-ray background at
redshift nine truncated above 1 Rydberg. At the redshift or re-ionization, we
additionally inject a fixed user-defined amount of energy per unit mass.
In addition to the tables we inject extra energy from Helium re-ionization using
a Gaussian model with a user-defined redshift for the centre, width and total
amount of energy injected per unit mass.
The cooling itself is performed using an implicit scheme (see the theory
documents) which for small values of the cooling rates is solved explicitly. For
larger values we use a bisection scheme. Users can alternatively use a
Newton-Raphson method that in some cases runs faster than the bisection
method. If the Newton-Raphson method does not converge after a few steps, the
code reverts to a bisection scheme, that is guaranteed to converge. The cooling
rate is added to the calculated change in energy over time from the other
dynamical equations. This is different from other commonly used codes in the
literature where the cooling is done instantaneously.
We note that the EAGLE cooling model does not impose any restriction on the
particles' individual time-steps. The cooling takes place over the time span
given by the other conditions (e.g the Courant condition).
Particle tracers
~~~~~~~~~~~~~~~~
......@@ -152,11 +199,11 @@ Particle tracers
Star formation: Schaye+2008
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Stellar enrichment: Wiersma+2008b
Stellar enrichment: Wiersma+2009b
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Supernova feedback: Schaye+2012
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Supernova feedback: Dalla Vecchia+2012
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Black-hole creation
~~~~~~~~~~~~~~~~~~~
......
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