123 research outputs found
XMM-Newton and Chandra Cross Calibration Using HIFLUGCS Galaxy Clusters: Systematic Temperature Differences and Cosmological Impact
Cosmological constraints from clusters rely on accurate gravitational mass
estimates, which strongly depend on cluster gas temperature measurements.
Therefore, systematic calibration differences may result in biased,
instrument-dependent cosmological constraints. This is of special interest in
the light of the tension between the Planck results of the primary temperature
anisotropies of the CMB and Sunyaev-Zel'dovich plus X-ray cluster counts
analyses. We quantify in detail the systematics and uncertainties of the
cross-calibration of the effective area between five X-ray instruments,
EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the
influence on temperature measurements. Furthermore, we assess the impact of the
cross calibration uncertainties on cosmology. Using the HIFLUGCS sample,
consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM
temperatures through spectral fitting in the same, mostly isothermal, regions
and compare them. Our work is an extension to a previous one using X-ray
clusters by the IACHEC. Performing spectral fitting in the full energy band we
find that best-fit temperatures determined with XMM-Newton/EPIC are
significantly lower than Chandra/ACIS temperatures. We demonstrate that effects
like multitemperature structure and different relative sensitivities of the
instruments at certain energy bands cannot explain the observed differences. We
conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full
energy band temperature profiles for cluster mass determination results in an
8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values
in a cosmological analysis of a complete sample of galaxy clusters. Such a
shift is insufficient to significantly alleviate the tension between Planck CMB
anisotropies and SZ plus XMM-Newton cosmological constraints.Comment: Accepted by A&A; Python-Script for modification of XMM-Newton/EPIC
and Chandra/ACIS effective areas according to the stacked residual ratios:
https://wikis.mit.edu/confluence/display/iachec/Data
Scaling relations for galaxy clusters: properties and evolution
Well-calibrated scaling relations between the observable properties and the
total masses of clusters of galaxies are important for understanding the
physical processes that give rise to these relations. They are also a critical
ingredient for studies that aim to constrain cosmological parameters using
galaxy clusters. For this reason much effort has been spent during the last
decade to better understand and interpret relations of the properties of the
intra-cluster medium. Improved X-ray data have expanded the mass range down to
galaxy groups, whereas SZ surveys have openened a new observational window on
the intracluster medium. In addition,continued progress in the performance of
cosmological simulations has allowed a better understanding of the physical
processes and selection effects affecting the observed scaling relations. Here
we review the recent literature on various scaling relations, focussing on the
latest observational measurements and the progress in our understanding of the
deviations from self similarity.Comment: 38 pages. Review paper. Accepted for publication in Space Science
Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done
by an international team at the International Space Science Institute (ISSI)
in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and
Lensing View
XMM Observations of Metal Abundances in Galaxy Clusters
The hot gas that fills the space between galaxies in clusters is rich in metals. Due to their large potential well, galaxy clusters accumulate metals over the whole history of the cluster, and retain important information on cluster formation and evolution.We derive detailed metallicity maps for a sample of 5 clusters, observed with XMM-Newton, to study the distribution of metals in the Intra-Cluster Medium (ICM). We show that even in relaxed clusters the distribution of metals shows many inhomogeneities with several maxima separated by low metallicity regions. We also found a deviation from the expected temperature-metallicity relation
From "universal" profiles to "universal" scaling laws in X-ray galaxy clusters
As the end products of the hierarchical process of cosmic structure
formation, galaxy clusters present some predictable properties, like those
mostly driven by gravity, and some others, more affected by astrophysical
dissipative processes, that can be recovered from observations and that show
remarkable "universal" behaviour once rescaled by halo mass and redshift.
However, a consistent picture that links these universal radial profiles and
the integrated values of the thermodynamical quantities of the intracluster
medium, also quantifying the deviations from the standard self-similar
gravity-driven scenario, has to be demonstrated. In this work, we use a
semi-analytic model based on a universal pressure profile in hydrostatic
equilibrium within a cold dark matter halo with a defined relation between mass
and concentration to reconstruct the scaling laws between the X-ray properties
of galaxy clusters. We also quantify any deviation from the self-similar
predictions in terms of temperature dependence of a few physical quantities
such as the gas mass fraction, the relation between spectroscopic temperature
and its global value, and, if present, the hydrostatic mass bias. This model
allows to reconstruct both the observed profiles and the scaling laws between
integrated quantities. We use the Planck-selected ESZ sample to calibrate the
predicted scaling laws between gas mass, temperature, luminosity and total
mass. Our universal model reproduces well the observed thermodynamic properties
and provides a way to interpret the observed deviations from the standard
self-similar behaviour. By combining these results with the constraints on the
observed relation, we show how we can quantify the level of gas
clumping affecting the studied sample, estimate the clumping-free gas mass
fraction, and suggest the average level of hydrostatic bias present.Comment: 13 pages. A&A in press. Minor update to fix typos and better match
published versio
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
Extending the relation from clusters to groups-Impact of cool core nature, AGN feedback, and selection effects
We aim to investigate the bolometric relation for galaxy
groups, and study the impact of gas cooling, feedback from supermassive black
holes, and selection effects on it. With a sample of 26 galaxy groups we
obtained the best fit relation for five different cases
depending on the ICM core properties and central AGN radio emission, and
determined the slopes, normalisations, intrinsic and statistical scatters for
both temperature and luminosity. Simulations were undertaken to correct for
selection effects (e.g. Malmquist bias) and the bias corrected relations for
groups and clusters were compared. The slope of the bias corrected
relation is marginally steeper but consistent with clusters
(). Groups with a central cooling time less than 1 Gyr (SCC groups)
show indications of having the steepest slope and the highest normalisation.
For the groups, the bias corrected intrinsic scatter in is
larger than the observed scatter for most cases, which is reported here for the
first time. Lastly, we see indications that the groups with an extended central
radio source have a much steeper slope than those groups which have a CRS with
only core emission. Additionally, we also see indications that the more
powerful radio AGN are preferentially located in NSCC groups rather than SCC
groups.Comment: Accepted for publication in Astronomy and Astrophysic
Stormy weather in 3C 196.1: nuclear outbursts and merger events shape the environment of the hybrid radio galaxy 3C 196.1
We present a multi-wavelength analysis based on archival radio, optical and
X-ray data of the complex radio source 3C 196.1, whose host is the brightest
cluster galaxy of a cluster. HST data show H+[N II] emission
aligned with the jet 8.4 GHz radio emission. An H+[N II] filament
coincides with the brightest X-ray emission, the northern hotspot. Analysis of
the X-ray and radio images reveals cavities located at galactic- and cluster-
scales. The galactic-scale cavity is almost devoid of 8.4 GHz radio emission
and the south-western H+[N II] emission is bounded (in projection) by
this cavity. The outer cavity is co-spatial with the peak of 147 MHz radio
emission, and hence we interpret this depression in X-ray surface brightness as
being caused by a buoyantly rising bubble originating from an AGN outburst
280 Myrs ago. A \textit{Chandra} snapshot observation allowed us to
constrain the physical parameters of the cluster, which has a cool core with a
low central temperature 2.8 keV, low central entropy index 13 keV
cm and a short cooling time of 500 Myr, which is of the age
of the Universe at this redshift. By fitting jumps in the X-ray density we
found Mach numbers between 1.4 and 1.6, consistent with a shock origin. We also
found compelling evidence of a past merger, indicated by a morphology
reminiscent of gas sloshing in the X-ray residual image. Finally, we computed
the pressures, enthalpies and jet powers associated with
the cavities: erg,
erg s for the inner cavity and erg,
erg s for the outer cavity.Comment: 14 pages, 4 figures, ApJ accepte
The radio relic in Abell 2256: overall spectrum and implications for electron acceleration
The galaxy cluster Abell 2256 hosts one of the most intriguing examples in
the class of radio relics. It has been found that this radio relic has a rather
flat integrated spectrum at low frequencies that would imply an injection
spectral index for the electrons that is inconsistent with the flattest allowed
by the test particle diffusive shock acceleration (DSA). We performed new
high-frequency observations at 2273, 2640, and 4850 MHz. Combining these new
observations with images available in the literature, we constrain the radio
integrated spectrum of the radio relic in Abell 2256 over the widest sampled
frequency range collected so far for this class of objects (63 -10450 MHz).
Moreover, we used X-ray observations of the cluster to check the temperature
structure in the regions around the radio relic. We find that the relic keeps
an unusually flat behavior up to high frequencies. Although the relic
integrated spectrum between 63 and 10450 MHz is not inconsistent with a single
power law with , we find hints of a
steepening at frequencies > 1400 MHz. The two frequency ranges 63-1369 MHz and
1369-10450 MHz are, indeed, best represented by two different power laws, with
and .
This broken power law would require special conditions to be explained in terms
of test-particle DSA, e.g., non-stationarity of the spectrum and/or
non-stationarity of the shock. On the other hand, the single power law would
make of this relic the one with the flattest integrated spectrum known so far,
even flatter than what allowed in the test-particle approach to DSA. We find a
rather low temperature ratio of across the G region of the
radio relic and no temperature jump across the H region.Comment: 18 pages, 11 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
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