We present the first measurements of the abundances of $alpha$-elements (Mg, Si, and S) extending out to beyond the virial radius of a cluster of galaxies. Our results, based on Suzaku Key Project observations of the Virgo Cluster, show that the chem
ical composition of the intra-cluster medium is consistent with being constant on large scales, with a flat distribution of the Si/Fe, S/Fe, and Mg/Fe ratios as a function of radius and azimuth out to 1.4 Mpc (1.3 $r_{200}$). Chemical enrichment of the intergalactic medium due solely to core collapse supernovae (SNcc) is excluded with very high significance; instead, the measured metal abundance ratios are generally consistent with the Solar value. The uniform metal abundance ratios observed today are likely the result of an early phase of enrichment and mixing, with both SNcc and type Ia supernovae (SNIa) contributing to the metal budget during the period of peak star formation activity at redshifts of 2-3. We estimate the ratio between the number of SNIa and the total number of supernovae enriching the intergalactic medium to be between 12-37%, broadly consistent with the metal abundance patterns in our own Galaxy or with the SNIa contribution estimated for the cluster cores.
We present the results from extensive, new observations of the Perseus Cluster of galaxies, obtained as a Suzaku Key Project. The 85 pointings analyzed span eight azimuthal directions out to 2 degrees = 2.6 Mpc, to and beyond the virial radius r_200
~ 1.8 Mpc, offering the most detailed X-ray observation of the intracluster medium (ICM) at large radii in any cluster to date. The azimuthally averaged density profile for r>0.4r_200 is relatively flat, with a best-fit power-law index of 1.69+/-0.13 significantly smaller than expected from numerical simulations. The entropy profile in the outskirts lies systematically below the power-law behavior expected from large-scale structure formation models which include only the heating associated with gravitational collapse. The pressure profile beyond ~0.6r_200 shows an excess with respect to the best-fit model describing the SZ measurements for a sample of clusters observed with Planck. The inconsistency between the expected and measured density, entropy, and pressure profiles can be explained primarily by an overestimation of the density due to inhomogeneous gas distribution in the outskirts; there is no evidence for a bias in the temperature measurements within the virial radius. We find significant differences in thermodynamic properties of the ICM at large radii along the different arms. Along the cluster minor axis, we find a flattening of the entropy profiles outside ~0.6r_200, while along the major axis, the entropy rises all the way to the outskirts. Correspondingly, the inferred gas clumping factor is typically larger along the minor than along the major axis.
Multiwavelength studies of radio relics at merger shocks set powerful constraints on the relics origin and formation mechanism. However, for X-ray observations, a main difficulty is represented by the low X-ray surface brightness far out in the clust
er outskirts, where relics are typically found. Here, we present XMM-Newton results from a 130-ks observation of CIZA J2242.8+5301, a cluster at z=0.19 that hosts a double radio relic. We focus on the well-defined northern relic. There is a difference of ~55% between the temperature we measure behind the relic, and the temperature measured with Suzaku. We analyse the reasons for this large discrepancy, and discuss the possibility of reliably measuring the temperature beyond the northern relic.
(abridged) Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of $sim$16,000 independent regions, each with $sim$1,000 net counts. The excellent spatial resolution of the thermodynamic maps
reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. Excluding the X-ray arms, the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift, or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions. We confirm the presence of a thick ($sim$40 arcsec or $sim$3 kpc) ring of high pressure gas at a radius of $sim$180 arcsec ($sim$14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M = 1.25. Another, younger shock-like feature is observed at a radius of $sim$40 arcsec ($sim$3 kpc) surrounding the central AGN, with an estimated Mach number M > 1.2. As shown previously, if repeated shocks occur every $sim$10 Myrs, as suggested by these observations, then AGN driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350 - 400 arcsec (27 - 31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least $sim1.0times10^6$ solar masses of Fe has been lifted and deposited at a radius of 350-400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350 - 400 arcsec.
We present multi-wavelength observations of the centre of RXCJ1504.1-0248 - the galaxy cluster with the most luminous and relatively nearby cool core at z~0.2. Although there are several galaxies within 100 kpc of the cluster core, only the brightest
cluster galaxy (BCG), which lies at the peak of the X-ray emission, has blue colours and strong line-emission. Approximately 80 Msun/yr of intracluster gas is cooling below X-ray emitting temperatures, similar to the observed UV star formation rate of ~140 Msun/yr. Most star formation occurs in the core of the BCG and in a 42 kpc long filament of blue continuum, line emission, and X-ray emission, that extends southwest of the galaxy. The surrounding filamentary nebula is the most luminous around any observed BCG. The number of ionizing stars in the BCG is barely sufficient to ionize and heat the nebula, and the line ratios indicate an additional heat source is needed. This heat source can contribute to the Halpha-deduced star formation rates (SFRs) in BCGs and therefore the derived SFRs should only be considered upper limits. AGN feedback can slow down the cooling flow to the observed mass deposition rate if the black hole accretion rate is of the order of 0.5 Msun/yr at 10% energy output efficiency. The average turbulent velocity of the nebula is vturb ~325 km/s which, if shared by the hot gas, limits the ratio of turbulent to thermal energy of the intracluster medium to less than 6%.
Current high resolution observations of galaxy clusters reveal a dynamical intracluster medium (ICM). The wealth of structures includes signatures of interactions between active galactic nuclei (AGN) and the ICM, such as cavities and shocks, as well
as signatures of bulk motions, e.g. cold fronts. Aiming at understanding the physics of the ICM, we study individual clusters by both, deep high resolution observations and numerical simulations which include processes suspected to be at work, and aim at reproducing the observed properties. By comparing observations and simulations in detail, we gain deeper insights into cluster properties and processes. Here we present two examples of our approach: the large-scale shock in the Hydra A cluster, and sloshing cold fronts.
We analyzed global properties, radial profiles and 2D maps of the metal abundances and temperature in the cool core cluster of galaxies Hydra A using a deep XMM-Newton exposure. The best fit among the available spectral models is provided by a Gaussi
an distribution of the emission measure (gdem). We can accurately determine abundances for 7 elements in the cluster core with EPIC and 3 elements with RGS. The gdem model gives lower Fe abundances than a single temperature model. The abundance profiles for Fe, Si, S, but also O are centrally peaked. Combining the Hydra A results with 5 other clusters for which detailed chemical abundance studies are available, we find a significant decrease of O with radius, while the increase in the O/Fe ratio with radius is small within 0.1 r_200. We compare the observed abundance ratios with the mixing of various supernova type Ia and core-collapse yield models in different relative amounts. Producing the estimated O, Si and S peaks in Hydra A requires either an amount of metals ejected by stellar winds 3-8 times higher than predicted by available models or a remaining peak in the enrichment by core-collapse supernovae from the protocluster phase. The temperature map shows cooler gas extending in arm-like structures towards the north and south. These structures appear to be richer in metals than the ambient medium and spatially correlated with the large-scale radio lobes. We estimate the mass of cool gas, which was probably uplifted by buoyant bubbles of relativistic plasma produced by the AGN, to 1.6-6.1x10^9 M_sun, and the energy associated with this uplift to 3.3-12.5x10^58 ergs. The best estimate of the mass of Fe uplifted together with the cool gas is 1.7x10^7 M_sun, 15% of the total mass of Fe in the central 0.5arcmin region.
