167 research outputs found
Occurence and Luminosity Functions of Giant Radio Halos from Magneto-Turbulent Model
We calculate the probability to form giant radio halos (~ 1 Mpc size) as a
function of the mass of the host clusters by using a Statistical
Magneto-Turbulent Model (Cassano & Brunetti, these proceedings). We show that
the expectations of this model are in good agreement with the observations for
viable values of the parameters. In particular, the abrupt increase of the
probability to find radio halos in the more massive galaxy clusters (M >
2x10^{15} solar masses) can be well reproduced. We calculate the evolution with
redshift of such a probability and find that giant radio halos can be powered
by particle acceleration due to MHD turbulence up to z~0.5 in a LCDM cosmology.
Finally, we calculate the expected Luminosity Functions of radio halos (RHLFs).
At variance with previous studies, the shape of our RHLFs is characterized by
the presence of a cut-off at low synchrotron powers which reflects the
inefficiency of particle acceleration in the case of less massive galaxy
clusters.Comment: 4 pages, to appear in a dedicated issue of the Journal of the Korean
Astronomical Society (JKAS). Proceedings of the "International conference on
Cosmic Rays and Magnetic Fields in Large Scale Structure", Busan, Korea, 200
Non-thermal phenomena in galaxies clusters
The discovery of diffuse synchrotron radio emission and, more recently, of
the hard X-ray (HXR) tails have triggered a growing interest about non-thermal
phenomena in galaxy clusters. After a brief review of the most important
evidences for non-thermal emission, I will focus on the origin of the emitting
particles and of the hadronic component. In particular I will describe the
particle-injection and -acceleration mechanisms at work in the intra-cluster
medium (ICM) and, at the same time, discuss the possibility to test current
modellings of these phenomena with future radio, HXR, and gamma rays
observatories.Comment: 7 pages, 4 figures, Invited Talk in IAU colloquium 195-"Outskirts of
galaxy clusters: intense life in the suburbs", Torino, Italy, March 12-16,
200
Radio-continuum surveys with SKA and LOFAR: a first look at the perspectives for radio mini-halos
Diffuse synchrotron radio emission has been observed in a number of cool-core
clusters on scales comparable to that of the cooling region. These radio
sources are called `mini-halos'. In order to understand their origin, which is
still unclear, joint radio and X-ray statistical studies of large cluster
samples are necessary to investigate the radio mini-halo properties and their
connection with the cluster thermodynamics. We here extend our previous
explorative study and investigate the perspectives offered by surveys in the
radio continuum with LOFAR and SKA, in particular examining the effect of the
intra-cluster magnetic field in the mini-halo region for the first time. By
considering the minimum flux detectable in radio surveys and exploiting the
correlation observed for known mini-halos, we estimate the
detection limits achievable by future radio observational follow-up of X-ray
cluster samples, such as HIFLUGCS and eROSITA. This allows us to estimate the
maximum number of radio mini-halos that can potentially be discovered in future
surveys as a function of redshift and magnetic field strength. We show that
future radio surveys with LOFAR and SKA1 (at 140 MHz and 1.4 GHz) have the
potential to discover ~1,000-10,000 radio mini-halo candidates up to redshift
z=1. We further note that future SKA1 radio surveys at redshift z>0.6 will
allow us to distinguish between different magnetic fields in the mini-halo
region, because higher magnetic fields are expected to produce more powerful
mini-halos, thus implying a larger number of mini-halo detected at high
redshift. For example, the non-detection with SKA1 of mini-halos at z>0.6 will
suggest a low magnetic field (B < few G). The synergy of these radio
surveys with future X-ray observations and theoretical studies is essential in
establishing the radio mini-halo physical nature. [abridged]Comment: Accepted for publication in A&A; 9 pages, 9 figures. Revised to match
the corrected version after language editin
Rise and Fall of Radio Halos in Simulated Merging Galaxy Clusters
We present the first high resolution MHD simulation of cosmic-ray electron
reacceleration by turbulence in cluster mergers. We use an idealised model for
cluster mergers, combined with a numerical model for the injection, cooling and
reacceleration of cosmic-ray electrons, to investigate the evolution of cluster
scale radio emission in these objects. In line with theoretical expectations,
we for the first time, show in a simulation that reacceleration of CRe has the
potential to reproduce key observables of radio halos. In particular, we show
that clusters evolve being radio loud or radio quiet, depending on their
evolutionary stage during the merger. We thus recover the observed transient
nature of radio halos. In the simulation the diffuse emission traces the
complex interplay between spatial distribution of turbulence injected by the
halo infall and the spatial distribution of the seed electrons to reaccelerate.
During the formation and evolution of the halo the synchrotron emission spectra
show the observed variety: from power-laws with spectral index of 1 to 1.3 to
curved and ultra-steep spectra with index
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