70 research outputs found
Cold fronts in galaxy clusters
Cold fronts have been observed in a large number of galaxy clusters.
Understanding their nature and origin is of primary importance for the
investigation of the internal dynamics of clusters. To gain insight on the
nature of these features, we carry out a statistical investigation of their
occurrence in a sample of galaxy clusters observed with XMM-Newton and we
correlate their presence with different cluster properties. We have selected a
sample of 45 clusters starting from the B55 flux limited sample by Edge et al.
(1990) and performed a systematic search of cold fronts. We find that a large
fraction of clusters host at least one cold front. Cold fronts are easily
detected in all systems that are manifestly undergoing a merger event in the
plane of the sky while the presence of such features in the remaining clusters
is related to the presence of a steep entropy gradient, in agreement with
theoretical expectations. Assuming that cold fronts in cool core clusters are
triggered by minor merger events, we estimate a minimum of 1/3 merging events
per halo per Gyr.Comment: Accepted for publication in Astronomy & Astrophysics. Version with
full resolution figures available at:
http://www.iasf-milano.inaf.it/~simona/pub/coldfronts/ghizzardi.pd
On the Fe abundance peak formation in cool-core clusters of galaxies: hints from cluster WARPJ1415.1+3612 at z=1.03
We present a detailed study of the iron content of the core of the
high-redshift cluster WARPJ1415.1+3612 (z=1.03). By comparing the central Fe
mass excess observed in this system, M_Fe^exc = (1.67 +/- 0.40) x 10^9 M_sun,
with those measured in local cool-core systems, we infer that the bulk of the
mass excess was already in place at z=1, when the age of the Universe was about
half of what it is today. Our measures point to an early and intense period of
star formation most likely associated with the formation of the BCG. Indeed, in
the case of the power-law delay time distribution with slope -1, which
reproduces the data of WARPJ1415.1+3612 best, half of the supernovae explode
within 0.4 Gyr of the formation of the BCG. Finally, while for local cool-core
clusters the Fe distribution is broader than the near infrared light
distribution of the BCG, in WARPJ1415.1+3612 the two distributions are
consistent, indicating that the process responsible for broadening the Fe
distribution in local systems has not yet started in this distant cluster.Comment: 10 pages, accepted for publication in A&A, minor language corrections
added in v
A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment
A detailed characterization of the particle induced background is fundamental
for many of the scientific objectives of the Athena X-ray telescope, thus an
adequate knowledge of the background that will be encountered by Athena is
desirable. Current X-ray telescopes have shown that the intensity of the
particle induced background can be highly variable. Different regions of the
magnetosphere can have very different environmental conditions, which can, in
principle, differently affect the particle induced background detected by the
instruments. We present results concerning the influence of the magnetospheric
environment on the background detected by EPIC instrument onboard XMM-Newton
through the estimate of the variation of the in-Field-of-View background excess
along the XMM-Newton orbit. An important contribution to the XMM background,
which may affect the Athena background as well, comes from soft proton flares.
Along with the flaring component a low-intensity component is also present. We
find that both show modest variations in the different magnetozones and that
the soft proton component shows a strong trend with the distance from Earth.Comment: To appear in Experimental Astronomy. Presented at AHEAD Background
Workshop, 28-30 November 2016. Rome, Ital
A Systematic Analysis of the XMM-Newton Background: I. Dataset and Extraction Procedures
XMM-Newton is the direct precursor of the future ESA ATHENA mission. A study
of its particle-induced background provides therefore significant insight for
the ATHENA mission design. We make use of about 12 years of data, products from
the third XMM-Newton catalog as well as FP7 EXTraS project to avoid celestial
sources contamination and to disentangle the different components of the
XMM-Newton particle-induced background. Within the ESA R&D AREMBES
collaboration, we built new analysis pipelines to study the different
components of this background: this covers time behavior as well as spectral
and spatial characteristics.Comment: To appear in Experimental Astronomy, presented at AHEAD Background
Workshop, 28-30 November 2016, Rome, Italy. 12 pages, 6 figure
Deep Chandra observations of the stripped galaxy group falling into Abell 2142
In the local Universe, the growth of massive galaxy clusters mainly operates through the continuous accretion of group-scale systems. The infalling group in Abell 2142 is the poster child of such an accreting group, and as such, it is an ideal target to study the astrophysical processes induced by structure formation. We present the results of a deep (200 ks) observation of this structure with Chandra that highlights the complexity of this system in exquisite detail. In the core of the group, the spatial resolution of Chandra reveals a leading edge and complex AGN-induced activity. The morphology of the stripped gas tail appears straight in the innermost 250 kpc, suggesting that magnetic draping efficiently shields the gas from its surroundings. However, beyond ~ 300 kpc from the core, the tail flares and the morphology becomes strongly irregular, which could be explained by a breaking of the drape, for example, caused by turbulent motions. The power spectrum of surface-brightness fluctuations is relatively flat (P2D â kâ»ÂČâÂł which indicates that thermal conduction is strongly inhibited even beyond the region where magnetic draping is effective. The amplitude of density fluctuations in the tail is consistent with a mild level of turbulence with a Mach number M3D ~ 0:1 -0:25. Overall, our results show that the processes leading to the thermalization and mixing of the infalling gas are slow and relatively inefficient
Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?
The origin of radio relics is usually explained via diffusive shock
acceleration (DSA) or re-acceleration of electrons at/from merger shocks in
galaxy clusters. The case of acceleration is challenged by the low predicted
efficiency of low-Mach number merger shocks, unable to explain the power
observed in most radio relics. In this Letter we present the discovery of a new
giant radio relic around the galaxy cluster Abell 2249 () using
LOFAR. It is special since it has the lowest surface brightness of all known
radio relics. We study its radio and X-ray properties combinig LOFAR data with
uGMRT, JVLA and XMM. This object has a total power of W Hz and integrated spectral index . We infer for this radio relic a lower bound on the magnetisation of
G, a shock Mach number of , and a low
acceleration efficiency consistent with DSA. This result suggests that a
missing population of relics may become visible thanks to the unprecedented
sensitivity of the new generation of radio telescopes.Comment: Letter, 5 pages, 4 figures, accepted for publication on MNRAS Letter
VizieR Online Data Catalog: X-ray_peak-BCG offset for PSZ1 clusters (Rossetti+, 2016)
The starting point of our analysis is the Planck cosmology sample (PSZ1-cosmo) described in Planck Collaboration XX (2014A&A...571A..20P). It is a high-purity subsample constructed from the first release of the Planck catalogue of SZ sources (Planck Collaboration XXIX, 2014A&A...571A..29P, Cat. VIII/91), by imposing a signal-to-noise ratio (S/N) threshold of 7 and applying a mask, that excludes the galactic plane and point sources leaving 65 per cent of the sky for the survey. It contains 189 bona fide clusters with associated redshifts and has been used for the cosmological analysis with cluster number counts described in Planck Collaboration XX (2014A&A...571A..20P). (2 data files)
A systematic analysis of the XMM-Newton background: II. Properties of the in-Field-Of-View excess component
We present an accurate characterization of the particle background behaviour on XMM-Newton based on the entire EPIC archive. This corresponds to the largest EPIC data set ever examined. Our results have been obtained thanks to the collaboration between the FP7 European program EXTraS and the ESA R&D ATHENA activity AREMBES. We used as a diagnostic an improved version of the diagnostic which compares the data collected in unexposed region of the detector with the region of the field of view in the EPIC-MOS. We will show that the in Field-of-View excess background is made up of two different components, one associated to flares produced by soft protons and the other one to a low-intensity background. Its origin needs to be further investigated
CHEX-MATE: pressure profiles of 6 galaxy clusters as seen by SPT and Planck
Pressure profiles are sensitive probes of the thermodynamic conditions and
the internal structure of galaxy clusters. The intra-cluster gas resides in
hydrostatic equilibrium within the Dark Matter gravitational potential.
However, this equilibrium may be perturbed, e.g. as a consequence of thermal
energy losses, feedback and non-thermal pressure supports. Accurate measures of
the gas pressure over the cosmic times are crucial to constrain the cluster
evolution as well as the contribution of astrophysical processes. In this work
we presented a novel algorithm to derive the pressure profiles of galaxy
clusters from the Sunyaev-Zeldovich (SZ) signal measured on a combination of
Planck and South Pole Telescope (SPT) observations. The synergy of the two
instruments made it possible to track the profiles on a wide range of spatial
scales. We exploited the sensitivity to the larger scales of the Planck
High-Frequency Instrument to observe the faint peripheries, and the higher
spatial resolution of SPT to solve the innermost regions. We developed a
two-step pipeline to take advantage of the specifications of each instrument.
We first performed a component separation on the two data-sets separately to
remove the background (CMB) and foreground (galactic emission) contaminants.
Then we jointly fitted a parametric pressure profile model on a combination of
Planck and SPT data. We validated our technique on a sample of 6 CHEX-MATE
clusters detected by SPT. We compare the results of the SZ analysis with
profiles derived from X-ray observations with XMM-Newton. We find an excellent
agreement between these two independent probes of the gas pressure structure.Comment: 19 pages, 13 figures, submitted to A&
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