We report results from a detailed study of the sloshing gas in the core of A496. We detected the low-temperature/entropy spiral feature found in several cores. We also found that conduction between ...the gas in the spiral and the ambient medium must be suppressed by more than one order of magnitude compared with the Spitzer conductivity. Intriguingly, while the gas in the spiral pattern features a higher metal abundance than the surrounding medium, it follows the relation of entropy vs metal abundance defined by gas outside the spiral. The most plausible explanation for this behavior is that the low-entropy metal-rich plasma that is lifted up through the cluster atmosphere by sloshing suffers little heating or mixing with the ambient medium. While sloshing appears to be capable of lifting up significant amount of gas, the limited heat exchange and mixing between gas within and outside the spiral implies that this mechanism is not at all effective in 1) permanently redistributing metals within the core region and 2) heating up the coolest and densest gas, thereby providing little or no contribution to the staving off of catastrophic cooling in cool cores.
Aims.
We study the chemical evolution of galaxy clusters by measuring the iron mass in the ICM after dissecting the abundance profiles into different components.
Methods.
We used
Chandra
archival ...observations of 186 morphologically regular clusters in the redshift range of 0.04, 1.07. For each cluster, we computed the azimuthally averaged iron abundance and gas density profiles. In particular, our aim is to identify a central peak in the iron distribution, which is associated with the central galaxy, and an approximately constant plateau reaching the largest observed radii, which is possibly associated with early enrichment that occurred before or shortly after achieving virialization within the cluster. We were able to firmly identify two components in the iron distribution in a significant fraction of the sample simply by relying on the fit of the iron abundance profile. From the abundance and ICM density profiles, we computed the iron mass included in the iron peak and iron plateau, and the gas mass-weighted iron abundance of the ICM out to an extraction radius of 0.4
r
500
and to
r
500
by extending the abundance profile as a constant.
Results.
We find that the iron plateau shows no evolution with redshift. On the other hand, we find a marginal (< 2
σ
c.l.) decrease with redshift in the iron mass included in the iron peak rescaled by the gas mass. We measure that the fraction of iron peak mass is typically a few percent (∼1%) of the total iron mass within
r
500
. Therefore, since the total iron mass budget is dominated by the plateau, we find consistently that the global gas mass-weighted iron abundance does not evolve significantly across our sample. We were also able to reproduce past claims of evolution in the global iron abundance, which turn out to be due to the use of cluster samples with different selection methods combined with the use of emission-weighted, instead of gas mass-weighted, abundance values. Finally, while the intrinsic scatter in the iron plateau mass is consistent with zero, the iron peak mass exhibits a large scatter, in line with the fact that the peak is produced after the virialization of the halo and depends on the formation history of the hosting cool core and the strength of the associated feedback processes.
Conclusions.
We conclude that only a spatially resolved approach can resolve the issue of iron abundance evolution in the ICM, reconciling the contradictory results obtained in the last ten years. Evolutionary effects below
z
∼ 1 are marginally measurable with present-day data, while at
z
> 1 the constraints are severely limited by poor knowledge of the high-
z
cluster population. The path towards a full and comprehensive chemical history of the ICM requires the application of high angular resolution X-ray bolometers and a dramatic increase in the number of faint, extended X-ray sources.
We show that there is a new class of gas tails-slingshot tails-that form as a subhalo (i.e., a subcluster or early-type cluster galaxy) moves away from the cluster center toward the apocenter of its ...orbit. These tails can point perpendicular or even opposite to the subhalo direction of motion, not tracing the recent orbital path. Thus, the observed tail direction can be misleading, and we caution against naive conclusions regarding the subhalo's direction of motion based on the tail direction. A head-tail morphology of a galaxy's or subcluster's gaseous atmosphere is usually attributed to ram pressure stripping, and the widely applied conclusion is that gas stripped tail traces the most recent orbit. However, during the slingshot tail stage, the subhalo is not being ram pressure stripped (RPS) and the tail is shaped by tidal forces more than just the ram pressure. Thus, applying a classic RPS scenario to a slingshot tail leads not only to an incorrect conclusion regarding the direction of motion but also to incorrect conclusions regarding the subhalo velocity, expected locations of shear flows, instabilities, and mixing. We describe the genesis and morphology of slingshot tails using data from binary cluster merger simulations and discuss their observable features and how to distinguish them from classic RPS tails. We identify three examples from the literature that are not RPS tails but slingshot tails and discuss other potential candidates.
We present the first metal abundance profiles for a representative sample of massive clusters. Our measurements extend to
R
500
and are corrected for a systematic error plaguing previous outskirt ...estimates. Our profiles flatten out at large radii, admittedly not a new result, however the radial range and representative nature of our sample extends its import well beyond previous findings. We find no evidence of segregation between cool-core and non-cool-core systems beyond ∼0.3
R
500
, implying that, as was found for thermodynamic properties, the physical state of the core does not affect global cluster properties. Our mean abundance within
R
500
shows a very modest scatter, < 15%, suggesting the enrichment process must be quite similar in all these massive systems. This is a new finding and has significant implications for feedback processes. Together with results from the thermodynamic properties presented in a previous X-COP paper, it affords a coherent picture in which feedback effects do not vary significantly from one system to another. By combining intra-cluster medium with stellar measurements we have found the amount of Fe diffused in the intra-cluster medium to be about ten times higher than that locked in stars. Although our estimates suggest, with some strength, that the measured iron mass in clusters is well in excess of the predicted one, systematic errors prevent us from making a definitive statement. Further advancements will only be possible when systematic uncertainties, principally those associated with stellar masses, both within and beyond
R
500
, can be reduced.
In intermediate-mass galaxy clusters (
M
= 2 − 4 × 10
14
M
⊙
, or equivalently
T
= 2.5 − 4.5 keV), abundance measurements are almost equally driven by iron K and L transitions at ∼6.7 keV and 0.9 ...− 1.3 keV, respectively. While K-shell-derived measurements are considered reliable, the resolution of the currently available instrumentation, as well as our current knowledge of the atomic processes, makes the modelling of the L-line complex challenging, resulting in potential biases for abundance measurements. In this work we study with unprecedented accuracy the systematics related to the modelling of the Fe L-line complex that may influence iron-abundance measurements in the intermediate-mass range. To this end, we selected a sample of three bright and nearby galaxy clusters, with long
XMM-Newton
observations available and temperatures in the 2.5 − 4.5 keV range. We fit the spectra extracted from concentric rings with APEC and APEC+APEC models, by alternately excluding one band (L-shell or K
α
) at a time, and derived the fractional difference of the metal abundances Δ
Z
/
Z
as an indication of the consistency between K- and L-shell-derived measurements. The Δ
Z
/
Z
distribution was then studied as a function of the cluster radius, ring temperature, and X-ray flux. The L-blend-induced systematics, measured through an individual fit of each
XMM-Newton
MOS and pn camera spectrum, remain constant at a 5 − 6% value in the whole 2.5 − 4.5 keV temperature range. Conversely, a joint fit of MOS and pn spectra leads to a slight excess of 1 − 2% in this estimate. No significant dependence on the ring X-ray flux is highlighted. The measured 5 − 8% value indicates a modest contribution of the systematics to the derived iron abundances, giving confidence for future measurements. To date, these findings represent the best achievable estimate of the systematics in analysis, while future microcalorimeters will significantly improve our understanding of the atomic processes underlying the Fe L emissions.
The crisis of the standard cooling flow model brought about by Chandra and XMM-Newton observations of galaxy clusters has led to the development of several models that explore different heating ...processes in order to assess whether they can quench the cooling flow. Among the most appealing mechanisms are thermal conduction and heating through buoyant gas deposited in the intracluster medium (ICM) by active galactic nuclei (AGNs). We combine Virgo/M87 observations of three satellites (Chandra, XMM-Newton, and BeppoSAX) to inspect the dynamics of the ICM in the center of the cluster. Using the spectral deprojection technique, we derive the physical quantities describing the ICM and determine the extra heating needed to balance the cooling flow, assuming that thermal conduction operates at a fixed fraction of the Spitzer value. We assume that the extra heating is due to buoyant gas, and we fit the data using the model developed by Ruszkowski and Begelman. We derive a scale radius for the model of approx5 kpc, which is comparable with the M87 AGN jet extension, and a required luminosity of the AGN of a few x 10 super(42) ergs s super(- 1), which is comparable to the observed AGN luminosity. We discuss a scenario in which the buoyant bubbles are filled with relativistic particles and magnetic field, which are responsible for the radio emission in M87. The AGN is supposed to be intermittent and to inject populations of buoyant bubbles through a succession of outbursts. We also study the X-ray-cool component detected in the radio lobes and suggest that it is structured in blobs that are tied to the radio buoyant bubbles.
We report results from a detailed study of the sloshing gas in the core of A496. We detected the low-temperature/entropy spiral feature found in several cores. We also found that conduction between ...the gas in the spiral and the ambient medium must be suppressed by more than one order of magnitude compared with the Spitzer conductivity. Intriguingly, while the gas in the spiral pattern features a higher metal abundance than the surrounding medium, it follows the relation of entropy vs metal abundance defined by gas outside the spiral. The most plausible explanation for this behavior is that the low-entropy metal-rich plasma that is lifted up through the cluster atmosphere by sloshing suffers little heating or mixing with the ambient medium. While sloshing appears to be capable of lifting up significant amount of gas, the limited heat exchange and mixing between gas within and outside the spiral implies that this mechanism is not at all effective in 1) permanently redistributing metals within the core region and 2) heating up the coolest and densest gas, thereby providing little or no contribution to the staving off of catastrophic cooling in cool cores.
Galaxy clusters are the products of structure formation through myriad physical processes that affect their growth and evolution throughout cosmic history. As a result, the matter distribution within ...galaxy clusters, or their shape, is influenced by cosmology and astrophysical processes, in particular the accretion of new material due to gravity. We introduce an analysis method for investigating the three-dimensional triaxial shapes of galaxy clusters from the Cluster HEritage project with XMM-Newton – Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE). In this paper, the first in a CHEX-MATE triaxial analysis series, we focus on utilizing X-ray data from XMM-Newton and Sunyaev–Zel’dovich (SZ) effect maps from Planck and the Atacama Cosmology Telescope to obtain a three-dimensional triaxial description of the intracluster medium (ICM) gas. We present the forward modeling formalism of our technique, which projects a triaxial ellipsoidal model for the gas density and pressure, to be compared directly with the observed two-dimensional distributions in X-rays and the SZ effect. A Markov chain Monte Carlo is used to estimate the posterior distributions of the model parameters. Using mock X-ray and SZ observations of a smooth model, we demonstrate that the method can reliably recover the true parameter values. In addition, we applied the analysis to reconstruct the gas shape from the observed data of one CHEX-MATE galaxy cluster, PSZ2 G313.33+61.13 (Abell 1689), to illustrate the technique. The inferred parameters are in agreement with previous analyses for the cluster, and our results indicate that the geometrical properties, including the axial ratios of the ICM distribution, are constrained to within a few percent. With a much better precision than previous studies, we thus further establish that Abell 1689 is significantly elongated along the line of sight, resulting in its exceptional gravitational lensing properties.
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