291 research outputs found
Magnetorotational instability in cool cores of galaxy clusters
Clusters of galaxies are embedded in halos of optically thin, gravitationally
stratified, weakly magnetized plasma at the system's virial temperature. Due to
radiative cooling and anisotropic heat conduction, such intracluster medium
(ICM) is subject to local instabilities, which are combinations of the thermal,
magnetothermal and heat-flux-driven buoyancy instabilities. If the ICM rotates
significantly, its stability properties are substantially modified and, in
particular, also the magnetorotational instability (MRI) can play an important
role. We study simple models of rotating cool-core clusters and we demonstrate
that the MRI can be the dominant instability over significant portions of the
clusters, with possible implications for the dynamics and evolution of the cool
cores. Our results give further motivation for measuring the rotation of the
ICM with future X-ray missions such as ASTRO-H and ATHENA.Comment: 17 pages, 10 figures, accepted for publication in Journal of Plasma
Physics, Special Issue "Complex Plasma Phenomena in the Laboratory and in the
Universe
On a novel approach using massive clusters at high redshifts as cosmological probe
In this work we propose a novel method for testing the validity of the
fiducial LCDM cosmology by measuring the cumulative distribution function of
the most massive haloes in a sample of subvolumes of identical size tiled on
the sky at a fixed redshift. The fact that the most massive clusters probe the
high-mass tail of the mass function, where the difference between LCDM and
alternative cosmological models is strongest, makes our method particularly
interesting as a cosmological probe. We utilise general extreme value
statistics (GEV) to obtain a cumulative distribution function of the most
massive objects in a given volume. We sample this distribution function
according to the number of patches covered by the survey area for a range of
different "test cosmologies" and for differently accurate mass estimations of
the haloes. By fitting this sample with the GEV distribution function, we can
study which parameters are the most sensitive with respect to the test
cosmologies. We find that the peak of the probability distribution function of
the most massive halo is well suited to test the validity of the fiducial LCDM
model, once we are able to establish a sufficiently complete large-area survey
with M_lim=10^14.5 M_sun/h (M_lim=10^14 M_sun/h) at redshifts above z=1
(z=1.5). Being of cumulative nature the proposed measure is robust and an
accuracy of 20-30% in the cluster masses would be sufficient to test for
alternative models. Since one only needs the most massive system in each
angular patch, this method would be ideally suited as a first fast consistency
check before going into a more complex statistical analysis of the observed
halo sample.Comment: 11 pages, 13 figures, 1 Table, MNRAS accepted versio
CLASH-VLT: The inner slope of the MACS J1206.2-0847 mass density profile
The inner slope gammaDM of the dark matter (DM) density profile of
cosmological halos carries information about the properties of DM and/or
baryonic processes affecting the halo gravitational potential. Cold DM
cosmological simulations predict steep inner slopes, gammaDM>~1. We test this
prediction on the MACS J1206.2-0847 cluster at redshift z=0.44, whose DM
density profile was claimed to be cored at the center. We determine the cluster
DM density profile from 2 kpc from the cluster center to the virial radius (~2
Mpc), using the velocity distribution of ~500 cluster galaxies and the velocity
dispersion profile of the Brightest Cluster Galaxy (BCG), obtained from
VIMOS@VLT and MUSE@VLT data. We solve the Jeans equation of dynamical
equilibrium using an upgraded version of the MAMPOSSt method. The total mass
profile is modeled as a sum of a generalized-NFW profile that describes the DM
component, allowing for a free inner slope of the density profile, a Jaffe
profile that describes the BCG stellar mass component, and a non-parametric
baryonic profile that describes the sum of the remaining galaxy stellar mass
and of the hot intra-cluster gas mass. Our total mass profile is in remarkable
agreement with independent determinations based on X-ray observations and
strong lensing. We find gammaDM=0.7 -0.1 +0.2 (68% confidence levels),
consistent with predictions from recent LambdaCDM cosmological numerical
simulations.Comment: Submitted to ApJ on June, 1st 2023. 14 pages, 9 figure
Precessing jets from a moving source and bright X-ray filaments in galaxy clusters
We present hydrodynamical calculations carried out with the 3D yguazu-a code
of a precessing jet model, which interacts with a plane parallel wind. This
scenario describes an extragalactic jet, in which the jet source is in motion
with respect to the surrounding intra-cluster medium. From the numerical
results, synthetic emission maps and spectra in X-ray band were obtained. We
compare these predictions with observations of the radio jets emanating from
the radio-galaxy 4C 26.42 (in the Abell 1795 galaxy cluster). We find that the
general morphology of the radio jets can be described by a point-symmetric
precessing jet system interacting with a plane parallel wind (i.e., the
intra-cluster medium flowing past the galaxy). We also find that our synthetic
X-ray emission maps reproduce the observed large scale structures (with sizes
of the order of tens of kpc).Comment: Accepted for publication in A&A - 7 Pages, 6 figure
Conduction and cooling flows
Chandra and XMM-Newton observations have confirmed the presence of large
temperature gradients within the cores of many relaxed clusters of galaxies.
Here we investigate whether thermal conduction operating over those gradients
can supply sufficient heat to offset radiative cooling. Narayan & Medvedev
(2001) and Gruzinov (2002) have noted, using published results on cluster
temperatures, that conduction within a factor of a few of the Spitzer rate is
sufficient to balance bremsstrahlung cooling. From a detailed study of the
temperature and emission measure profiles of Abell 2199 and Abell 1835, we find
that the heat flux required by conduction is consistent with or below the rate
predicted by Spitzer in the outer regions of the core. Conduction may therefore
explain the lack of observational evidence for large mass cooling rates
inferred from arguments based simply on radiative cooling, provided that
conductivity is suppressed by no more than a factor of three below the full
Spitzer rate. To stem cooling in the cluster centre, however, would necessitate
conductivity values at least a factor of two larger than the Spitzer values,
which we consider implausible. This may provide an explanation for the observed
star formation and optical nebulosities in cluster cores. The solution is
likely to be time dependent. We briefly discuss the possible origin of the
cooler gas and the implications for massive galaxies.Comment: 5 pages, 4 figures, accepted by MNRAS. Minor changes following
referee's comment
Vitis vinifera - a chemotaxonomic approach: Seed storage proteins
The IEF pattern of the constituent peptides for the storage protein from Viris vinifera endosperm is used for the construction of a dendrogram relating 74 seed specimens
On the modelling of the excesses of galaxy clusters over high-mass thresholds
In this work we present for the first time an application of the Pareto
approach to the modelling of the excesses of galaxy clusters over high-mass
thresholds. The distribution of those excesses can be described by the
generalized Pareto distribution (GPD), which is closely related to the
generalized extreme value (GEV) distribution. After introducing the formalism,
we study the impact of different thresholds and redshift ranges on the
distributions, as well as the influence of the survey area on the mean excess
above a given mass threshold. We also show that both the GPD and the GEV
approach lead to identical results for rare, thus high-mass and high-redshift,
clusters. As an example, we apply the Pareto approach to ACT-CL J0102-4915 and
SPT-CL J2106-5844 and derive the respective cumulative distribution functions
of the exceedance over different mass thresholds. We also study the possibility
to use the GPD as a cosmological probe. Since in the maximum likelihood
estimation of the distribution parameters all the information from clusters
above the mass threshold is used, the GPD might offer an interesting
alternative to GEV-based methods that use only the maxima in patches. When
comparing the accuracy with which the parameters can be estimated, it turns out
that the patch-based modelling of maxima is superior to the Pareto approach. In
an ideal case, the GEV approach is capable to estimate the location parameter
with a percent level precision for less than 100 patches. This result makes the
GEV based approach potentially also interesting for cluster surveys with a
smaller area.Comment: 10 pages, 8 figures, MNRAS accepted, minor modifications to match the
accepted versio
Hydrodynamical simulations of galaxy clusters in dark energy cosmologies - I. General properties
We investigate the influence of dark energy on structure formation, within five different cosmological models, namely a concordance \u39bCDM model, two models with dynamical dark energy, viewed as a quintessence scalar field (using a RP and a SUGRA potential form) and two extended quintessence models (EQp and EQn) where the quintessence scalar field interacts non-minimally with gravity (scalar-tensor theories). We adopted for all models the normalization of the matter power spectrum \u3c38 to match the CMB data. In the models with dynamical dark energy and quintessence, we describe the equation of state with w0 48 120.9, still within the range allowed by observations. For each model, we have performed hydrodynamical simulations in a cosmological box of (300 Mpc h 121)3 including baryons and allowing for cooling and star formation. The contemporary presence of evolving dark energy and baryon physics allows us to investigate the interplay between the different background cosmology and the evolution of the luminous matter. Since cluster baryon fraction can be used to constrain other cosmological parameters such as \u3a9m, we also analyse how dark energy influences the baryon content of galaxy clusters. We find that, in models with dynamical dark energy, the evolving cosmological background leads to different star formation rates and different formation histories of galaxy clusters, but the baryon physics is not affected in a relevant way. We investigate several proxies of the cluster mass function based on X-ray observables like temperature, luminosity, Mgas, and Ygas. We conclude that the X-ray temperature and Mgas functions are better diagnostic to disentangle the growth of structures among different dark energy models. [Abridged
An XMM-Newton observation of the massive, relaxed galaxy cluster ClJ1226.9+3332 at z=0.89
A detailed X-ray analysis of an XMM-Newton observation of the high-redshift
(z=0.89) galaxy cluster ClJ1226.9+3332 is presented. The X-ray temperature is
found to be 11.5{+1.1}{-0.9}keV, the highest X-ray temperature of any cluster
at z>0.6. In contrast to MS1054-0321, the only other very hot cluster currently
known at z>0.8, ClJ1226.9+3332 features a relaxed X-ray morphology, and its
high overall gas temperature is not caused by one or several hot spots. The
system thus constitutes a unique example of a high redshift, high temperature,
relaxed cluster, for which the usual hydrostatic equilibrium assumption, and
the X-ray mass is most reliable. A temperature profile is constructed (for the
first time at this redshift) and is consistent with the cluster being
isothermal out to 45% of the virial radius. Within the virial radius
(corresponding to a measured overdensity of a factor of 200), a total mass of
(1.4+/-0.5)*10^15 M_solar is derived, with a gas mass fraction of 12+/-5%. The
bolometric X-ray luminosity is (5.3+/-0.2)*10^45 erg/s. The probabilities of
finding a cluster of this mass within the volume of the discovery X-ray survey
are 8*10^{-5} for Omega_M=1 and 0.64 for Omega_M=0.3, making Omega_M=1 highly
unlikely. The entropy profile suggests that entropy evolution is being
observed. The metal abundance (of Z=0.33{+0.14}{-0.10} Z_solar), gas mass
fraction, and gas distribution are consistent with those of local clusters;
thus the bulk of the metals were in place by z=0.89.Comment: 13 pages, 8 figures. Accepted for publication in MNRA
Chandra detection of the intracluster medium around 3C294 at z=1.786
We present a Chandra observation of the powerful radio galaxy 3C294 showing
clear evidence for a surrounding intracluster medium. At a redshift of 1.786
this is the most distant cluster of galaxies yet detected in X-rays. The radio
core is detected as a point source, which has a spectrum consistent with a
heavily-absorbed power law implying an intrinsic 2-10 keV luminosity of ~10^45
erg/s. A small excess of emission is associated with the southern radio
hotspots. The soft, diffuse emission from the intracluster medium is centred on
the radio source. It has an hour-glass shape in the N-S direction, extending to
radii of at least 100 kpc, well beyond the radio source. The X-ray spectrum of
this extended component is fit by a thermal model with temperature ~5 keV, or
by gas cooling from above 7 keV at rates of ~400-700 Msolar/yr. The rest-frame
0.3-10 keV luminosity of the cluster is ~4.5x10^44 erg/s. The existence of such
a cluster is consistent with a low density universe.Comment: 5 pages, 6 figures, accepted by MNRA
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