63 research outputs found
Cosmological Parameters from Observations of Galaxy Clusters
Studies of galaxy clusters have proved crucial in helping to establish the
standard model of cosmology, with a universe dominated by dark matter and dark
energy. A theoretical basis that describes clusters as massive,
multi-component, quasi-equilibrium systems is growing in its capability to
interpret multi-wavelength observations of expanding scope and sensitivity. We
review current cosmological results, including contributions to fundamental
physics, obtained from observations of galaxy clusters. These results are
consistent with and complementary to those from other methods. We highlight
several areas of opportunity for the next few years, and emphasize the need for
accurate modeling of survey selection and sources of systematic error.
Capitalizing on these opportunities will require a multi-wavelength approach
and the application of rigorous statistical frameworks, utilizing the combined
strengths of observers, simulators and theorists.Comment: 53 pages, 21 figures. To appear in Annual Review of Astronomy &
Astrophysic
XMM-Newton discovery of O VII emission from warm gas in clusters of galaxies
XMM-Newton recently discovered O VII line emission from ~2 million K gas near
the outer parts of several clusters of galaxies. This emission is attributed to
the Warm-Hot Intergalactic Medium. The original sample of clusters studied for
this purpose has been extended and two more clusters with a soft X-ray excess
have been found. We discuss the physical properties of the warm gas, in
particular the density, spatial extent, abundances and temperature.Comment: 8 pages, 3 figures, conference "Soft X-ray emission from clusters of
galaxies and related phenomena", ed. R. Lieu, Kluwer, in pres
Heating Hot Atmospheres with Active Galactic Nuclei
High resolution X-ray spectroscopy of the hot gas in galaxy clusters has
shown that the gas is not cooling to low temperatures at the predicted rates of
hundreds to thousands of solar masses per year. X-ray images have revealed
giant cavities and shock fronts in the hot gas that provide a direct and
relatively reliable means of measuring the energy injected into hot atmospheres
by active galactic nuclei (AGN). Average radio jet powers are near those
required to offset radiative losses and to suppress cooling in isolated giant
elliptical galaxies, and in larger systems up to the richest galaxy clusters.
This coincidence suggests that heating and cooling are coupled by feedback,
which suppresses star formation and the growth of luminous galaxies. How jet
energy is converted to heat and the degree to which other heating mechanisms
are contributing, eg. thermal conduction, are not well understood. Outburst
energies require substantial late growth of supermassive black holes. Unless
all of the approximately 10E62 erg required to suppress star formation is
deposited in the cooling regions of clusters, AGN outbursts must alter
large-scale properties of the intracluster medium.Comment: 60 pages, 12 figures, to appear in 1997 Annual Reviews of Astronomy
and Astrophysics. This version supersedes the April 2007 version in Reviews
in Advance (references and minor corrections were added), and is similar to
the one scheduled to appear in Volume 45 of ARA
The connection between radio halos and cluster mergers and the statistical properties of the radio halo population
We discuss the statistical properties of the radio halo population in galaxy
clusters. Radio bi-modality is observed in galaxy clusters: a fraction of
clusters host giant radio halos while the majority of clusters do not show
evidence of diffuse cluster-scale radio emission. The radio bi-modality has a
correspondence in terms of dynamical state of the hosting clusters showing that
merging clusters host radio halos and follow the well known radio--X-ray
correlation, while more relaxed clusters do not host radio halos and populate a
region well separated from that correlation. These evidences can be understood
in the framework of a scenario where merger-driven turbulence re-accelerate the
radio emitting electrons. We discuss the main statistical expectations of this
scenario underlining the important role of upcoming LOFAR surveys to test
present models.Comment: 11 pages, 2 figures, Invited talk at the conference "Diffuse
Relativistic Plasmas", Bangalore, 1-4 March 2011; accepted for publication in
the Journal of Astrophysics and Astronom
Clusters of galaxies : observational properties of the diffuse radio emission
Clusters of galaxies, as the largest virialized systems in the Universe, are
ideal laboratories to study the formation and evolution of cosmic
structures...(abridged)... Most of the detailed knowledge of galaxy clusters
has been obtained in recent years from the study of ICM through X-ray
Astronomy. At the same time, radio observations have proved that the ICM is
mixed with non-thermal components, i.e. highly relativistic particles and
large-scale magnetic fields, detected through their synchrotron emission. The
knowledge of the properties of these non-thermal ICM components has increased
significantly, owing to sensitive radio images and to the development of
theoretical models. Diffuse synchrotron radio emission in the central and
peripheral cluster regions has been found in many clusters. Moreover
large-scale magnetic fields appear to be present in all galaxy clusters, as
derived from Rotation Measure (RM) studies. Non-thermal components are linked
to the cluster X-ray properties, and to the cluster evolutionary stage, and are
crucial for a comprehensive physical description of the intracluster medium.
They play an important role in the cluster formation and evolution. We review
here the observational properties of diffuse non-thermal sources detected in
galaxy clusters: halos, relics and mini-halos. We discuss their classification
and properties. We report published results up to date and obtain and discuss
statistical properties. We present the properties of large-scale magnetic
fields in clusters and in even larger structures: filaments connecting galaxy
clusters. We summarize the current models of the origin of these cluster
components, and outline the improvements that are expected in this area from
future developments thanks to the new generation of radio telescopes.Comment: Accepted for the publication in The Astronomy and Astrophysics
Review. 58 pages, 26 figure
WHIM emission and the cluster soft excess: a model comparison
The confirmation of the cluster soft excess (CSE) by XMM-Newton has rekindled
interest as to its origin. The recent detections of CSE emission at large
cluster radii together with reports of OVII line emission associated with the
CSE has led many authors to conjecture that the CSE is, in fact, a signature of
the warm-hot intergalactic medium (WHIM). In this paper we test the scenario by
comparing the observed properties of the CSE with predictions based on models
of the WHIM. We find that emission from the WHIM in current models is 3 to 4
orders of magnitude too faint to explain the CSE. We discuss different
possibilities for this discrepancy including issues of simulation resolution
and scale, and the role of small density enhancements or galaxy groups. Our
final conclusion is that the WHIM alone is unlikely to be able to accout for
the observed flux of the CSE.Comment: ApJ in pres
Cosmological parameters from the clustering of AGN
We attempt to put constraints on different cosmological and biasing models by
combining the recent clustering results of X-ray sources in the local () and distant universe ().Comment: 9 pages, 3 figures, to be published in the proceedings of the ''2nd
Hellenic Cosmology Workshop'', Athens 2001, eds, Manolis Plionis & Spiros
Kotsaki
Hot gas flows on global and nuclear galactic scales
Since its discovery as an X-ray source with the Einstein Observatory, the hot
X-ray emitting interstellar medium of early-type galaxies has been studied
intensively, with observations of improving quality, and with extensive
modeling by means of numerical simulations. The main features of the hot gas
evolution are outlined here, focussing on the mass and energy input rates, the
relationship between the hot gas flow and the main properties characterizing
its host galaxy, the flow behavior on the nuclear and global galactic scales,
and the sensitivity of the flow to the shape of the stellar mass distribution
and the mean rotation velocity of the stars.Comment: 22 pages. Abbreviated version of chapter 2 of the book "Hot
Interstellar Matter in Elliptical Galaxies", Springer 201
A low-frequency radio halo associated with a cluster of galaxies
Clusters of galaxies are the largest gravitationally bound objects in the
Universe, containing about 10^15 solar masses of hot (10^8 K) gas, galaxies and
dark matter in a typical volume of about 10 Mpc^3. Magnetic fields and
relativistic particles are mixed with the gas as revealed by giant radio
haloes, which arise from diffuse, megaparsec-scale synchrotron radiation at
cluster center. Radio haloes require that the emitting electrons are
accelerated in situ (by turbulence), or are injected (as secondary particles)
by proton collisions into the intergalactic medium. They are found only in a
fraction of massive clusters that have complex dynamics, which suggests a
connection between these mechanisms and cluster mergers. Here we report a radio
halo at low frequencies associated with the merging cluster Abell 521. This
halo has an extremely steep radio spectrum, which implies a high frequency
cut-off; this makes the halo difficult to detect with observations at 1.4 GHz
(the frequency at which all other known radio haloes have been best studied).
The spectrum of the halo is inconsistent with a secondary origin of the
relativistic electrons, but instead supports turbulent acceleration, which
suggests that many radio haloes in the Universe should emit mainly at low
frequencies.Comment: 18 pages, 4 figures, Nature 455, 94
- …