5 research outputs found
Clusters of galaxies: beyond the thermal view
We present the work of an international team at the International Space
Science Institute (ISSI) in Bern that worked together to review the current
observational and theoretical status of the non-virialised X-ray emission
components in clusters of galaxies. The subject is important for the study of
large-scale hierarchical structure formation and to shed light on the "missing
baryon" problem. The topics of the team work include thermal emission and
absorption from the warm-hot intergalactic medium, non-thermal X-ray emission
in clusters of galaxies, physical processes and chemical enrichment of this
medium and clusters of galaxies, and the relationship between all these
processes. One of the main goals of the team is to write and discuss a series
of review papers on this subject. These reviews are intended as introductory
text and reference for scientists wishing to work actively in this field. The
team consists of sixteen experts in observations, theory and numerical
simulations.Comment: 6 pages, 1 figure, accepted for publication in Space Science Reviews,
special issue "Clusters of galaxies: beyond the thermal view", Editor J.S.
Kaastra, Chapter 1; work done by an international team at the International
Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov,
S. Schindler & J.A.M. Bleeke
Nonthermal phenomena in clusters of galaxies
Recent observations of high energy (> 20 keV) X-ray emission in a few
clusters of galaxies broaden our knowledge of physical phenomena in the
intracluster space. This emission is likely to be nonthermal, probably
resulting from Compton scattering of relativistic electrons by the cosmic
microwave background (CMB) radiation. Direct evidence for the presence of
relativistic electrons in some 50 clusters comes from measurements of extended
radio emission in their central regions. We briefly review the main results
from observations of extended regions of radio emission, and Faraday rotation
measurements of background and cluster radio sources. The main focus of the
review are searches for nonthermal X-ray emission conducted with past and
currently operating satellites, which yielded appreciable evidence for
nonthermal emission components in the spectra of a few clusters. This evidence
is clearly not unequivocal, due to substantial observational and systematic
uncertainties, in addition to virtually complete lack of spatial information.
If indeed the emission has its origin in Compton scattering of relativistic
electrons by the CMB, then the mean magnetic field strength and density of
relativistic electrons in the cluster can be directly determined. Knowledge of
these basic nonthermal quantities is valuable for the detailed description of
processes in intracluster gas and for the origin of magnetic fields.Comment: 23 pages, 7 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 5; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Dark Matter Annihilation around Intermediate Mass Black Holes: an update
The formation and evolution of Black Holes inevitably affects the
distribution of dark and baryonic matter in the neighborhood of the Black Hole.
These effects may be particularly relevant around Supermassive and Intermediate
Mass Black Holes (IMBHs), the formation of which can lead to large Dark Matter
overdensities, called {\em spikes} and {\em mini-spikes} respectively. Despite
being larger and more dense, spikes evolve at the very centers of galactic
halos, in regions where numerous dynamical effects tend to destroy them.
Mini-spikes may be more likely to survive, and they have been proposed as
worthwhile targets for indirect Dark Matter searches. We review here the
formation scenarios and the prospects for detection of mini-spikes, and we
present new estimates for the abundances of mini-spikes to illustrate the
sensitivity of such predictions to cosmological parameters and uncertainties
regarding the astrophysics of Black Hole formation at high redshift. We also
connect the IMBHs scenario to the recent measurements of cosmic-ray electron
and positron spectra by the PAMELA, ATIC, H.E.S.S., and Fermi collaborations.Comment: 12 pages, 7 figures. Invited contribution to NJP Focus Issue on "Dark
Matter and Particle Physics