The change in the CMB intensity due to Compton scattering of CMB photons off of thermal electrons in galaxy clusters, otherwise known as the Sunyaev-Zeldovich (S-Z) effect, can to a reasonable approximation be represented by a projection of the pressure field of a cluster. However, the full S-Z signal is a combination of thermal and kinetic contributions, and for large frequencies and high temperatures relativistic effects are important. For computing the full S-Z signal incorporating all of these effects, there is a library: SZpack (Chluba et al 2012).
ytSZ makes it possible to make projections of the full S-Z signal given the
properties of the thermal gas in the simulation using SZpack. SZpack has
several different options for computing the S-Z signal, from full
integrations to very good approximations. Since a full or even a
partial integration of the signal for each cell in the projection
would be prohibitively expensive, we use the method outlined in
Chluba et al 2013 to
expand the total S-Z signal in terms of moments of the projected optical
depth 
, projected electron temperature
, and velocities 
and
(their equation 18):
ytSZ makes projections of the various moments needed for the
calculation, and then the resulting projected fields are used to
compute the S-Z signal. In our implementation, the expansion is carried out
to first-order terms in and zeroth-order terms in
by default, but terms at higher-order can
be optionally included.
First, install SZpack by downloading version 1.1.1
here.
SZpack depends on GSL, which should
be installed such that the gsl-config executable is in your path.
Then, ytsz can be installed using pip, but pip needs to know where to
find the SZpack library. This can be done if you have compiled SZpack in
$HOME/SZpack.v1.1.1, or if you set the environment variable SZPACK to the
location of the SZpack.v1.1.1 directory before executing pip. Then,
# Optionally set location of the SZpack installation
export SZPACK=$HOME/mylibs/SZpack.v1.1.1
python -m pip install ytszOr you can clone the source and install from there:
# This case assumes that SZpack is installed in $HOME/SZpack.v1.1.1
git clone https://github.com/jzuhone/ytsz
cd ytsz
python -m pip install .