Christoph Pfrommer

The Physics of Galaxy Clusters
Clusters of galaxies are the largest and most recently gravitationallycollapsed
objects in the Universe. Hence they provide us the opportunity to study an
"ecosystem"  a volume that is a highdensity microcosm of the rest of the
Universe. Clusters are excellent laboratories for studying the rich
astrophysics of baryons and dark matter. At the same time, they are extremely
rare events, forming at sites of constructive interference of long waves in
the primordial density fluctuations. Hence, they are very sensitive tracers of
the growth of structure in the universe and the cosmological parameters
governing it, which puts them into focus of constraining the properties of
Dark Energy or to test whether our understanding of gravity is
complete.
This lecture will explain how clusters form and grow. We will encounter the rich
and interesting astrophysics that governs the physics of dark matter and baryons
in clusters. We will see how we can take advantage of these physical processes
to observe clusters and deepen our understanding of the underlying fundamental
physics. To this end we will frequently use the powerful technique of order
of magnitude estimates, a very useful tool for contemporary research in
astrophysics. The lecture aims at students who
 wish to extend and deepen their understanding of theoretical physics;
 are interested in astronomy and astrophysics; or
 (intend to) carry out a masters thesis or Ph.D. dissertation on an
astronomical or astrophysical subject.
The lectures will be held in English because they are part of the Masters
programme. Advanced Bachelor students are welcome. The lectures take place
every Tuesday, 9:15am to 11am at the seminar room at ARI (Mönchhofstrasse
1214), starting on April 17, 2012.
The (handwritten) lecture notes will be continuously updated and is available as a
PDF file with the following
outline.
Contents:
 Overview and background:
 What is a galaxy cluster? Insights from observations at various wavelengths
 The homogeneous Universe: geometry, dynamics, and content
 Evolution of the dark component:
 Growth of perturbations
 Statistics and nonlinear evolution, power spectra
 Spherical collapse model and connection to perturbation theory
 PressSchechter mass function, halo density profiles, virial masses
 Evolution of the baryonic component:
 Nonradiative physics
 Entropy and convective instability
 Scaling relations (ideal and real)
 Shocks and jump conditions
 Entropy generation by smooth accretion and hierarchical merging
 Radiative physics
 Radiative cooling and star formation
 Energy feedback (supernovae, active galactic nuclei)
 Transport processes of gas:
turbulence, conduction, thermal stability (without and with magnetic fields)
 Nonthermal processes
 Origin and transport of magnetic fields, magnetohydrodynamic turbulence
 Acceleration of cosmic rays (to first and second order), transport equation
 Cluster physics informed by different observables:
 Optical: galaxy properties and virial theorem
 Transforming galaxy populations: ram pressure, tidal effects, dynamical friction
 Weighting clusters (1): virial theorem
 Gravitational lensing
 Deflection angle, lens equation, Einstein radius, lensing potential
 Weighting clusters (2): strong and weak cluster lensing
 Xrays: gastrophysics at highresolution
 Weighting clusters (3): hydrostatic equilibrium masses (and biases)
 Kinematics of shocks and cold fronts
 Probing kinetic equilibrium with collisionless shocks
 Width of cold fronts  magnetic draping
 SunyaevZel'dovich (SZ) effect: the thermal energy content
 Thermal and kinetic SZ effect
 Properties and SZ scaling relation, SZ power spectrum
 Radio halos and relics: watching powerful shocks and plasma physics at work
Credit Points:
There won't be exercise classes. Students who wish to obtain credit points can
choose one research paper from a selection of "classical papers" (provided by
the lecturer) that they have to read and present at a minisymposium (which will
be held in the end of the lecture series). Other students are expected to
actively participate with questions. Diploma students can obtain a certificate
for this lecture which can be used for acceptance in astronomy as a minor
subject for the diploma. Bachelor and Masters students can use the credit
points for this lecture as usual.
The collection of papers and the assignment can be obtained as a
PDF file.
Literature:
