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Register a new userSuzaku observations of Abell 1835 outskirts: Deviation from hydrostatic equilibrium
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We present results of four-pointing Suzaku X-ray observations (total ~200 ks) of the intracluster medium (ICM) in the Abell 1835 galaxy cluster (kT ~ 8 keV, z = 0.253) out to the virial radius (r_vir ~ 2.9 Mpc) and beyond. Faint X-ray emission from the ICM out to r_vir is detected. The temperature gradually decreases with radius from ~8 keV in the inner region to ~2 keV at r_vir. The entropy profile is shown to flatten beyond r_500, in disagreement with the r_1.1 dependence predicted from the accretion shock heating model. The thermal pressure profile in the range 0.3r_500 < r < r_vir agrees well with that obtained from the stacked Sunyaev-Zeldovich effect observations with the Planck satellite. The hydrostatic mass profile in the cluster outskirts (r_500 < r < r_vir) falls well short of the weak lensing one derived from Subaru/Suprime-Cam observations, showing an unphysical decrease with radius. The gas mass fraction at r_vir defined with the lensing total mass agrees with the cosmic baryon fraction from the WMAP 7-year data. All these results indicate, rather than the gas-clumping effect, that the bulk of the ICM in the cluster outskirts is far from hydrostatic equilibrium and infalling matter retained some of its kinetic energy. Finally, combining with our recent Suzaku and lensing analysis of Abell 1689, a cluster of similar mass, temperature, and redshift, we show that the cluster temperature distribution in the outskirts is significantly correlated with the galaxy density field in the surrounding large-scale environment at (1-2)r_vir.
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The results of Suzaku observations of the outskirts of Abell 3395 including a large-scale structure filament toward Abell 3391 are presented. We measured temperature and abundance distributions from the southern outskirt of Abell 3395 to the north at the virial radius, where a filament structure has been found in the former X-ray and Sunyaev-Zeldovich effect observations between Abell 3391 and 3395. The overall temperature structure is consistent with the universal profile proposed by Okabe et al.(2014) for relaxed clusters except for the filament region. A hint of the ICM heating is found between the two clusters, which might be due to the interaction of them in the early phase of a cluster merger. Although we obtained relatively low metal abundance of $Z=0.169^{+0.164+0.009+0.018 }_{-0.150-0.004-0.015 }$ solar, where the first, second, and third errors are statistical, cosmic X-ray background systematic, and non X-ray background systematic, respectively, at the virial radius in the filament, our results are still consistent with the former results of other clusters ($Z sim 0.3$ solar) within errors. Therefore, our results are also consistent with the early enrichment scenario. We estimated Compton $y$ parameters only from X-ray results in the region between Abell 3391 and 3395 assuming a simple geometry. They are smaller than the previous SZ results with Planck satellite. The difference could be attributed to a more elaborate geometry such as a filament inclined to the line-of-sight direction, or underestimation of the X-ray temperature because of the unresolved multi-temperature structures or undetected hot X-ray emission of the shock heated gas.
We report the first Chandra detection of emission out to the virial radius in the cluster Abell 1835 at z=0.253. Our analysis of the soft X-ray surface brightness shows that emission is present out to a radial distance of 10 arcmin or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak temperature of 10 keV to the value at the virial radius. We model the Chandra data from the core to the virial radius and show that the steep temperature profile is not compatible with hydrostatic equilibrium of the hot gas, and that the gas is convectively unstable at the outskirts. A possible interpretation of the Chandra data is the presence of a second phase of warm-hot gas near the clusters virial radius that is not in hydrostatic equilibrium with the clusters potential. The observations are also consistent with an alternative scenario in which the gas is significantly clumped at large radii.
We report Suzaku observations of the galaxy cluster Abell 1795 that extend to r_200 ~ 2 Mpc, the radius within which the mean cluster mass density is 200 times the cosmic critical density. These observations are the first to probe the state of the intracluster medium in this object at r > 1.3 Mpc. We sample two disjoint sectors in the cluster outskirts (1.3 < r < 1.9 Mpc) and detect X-ray emission in only one of them to a limiting (3-sigma) soft X-ray surface brightness of B(0.5-2 keV) = 1.8 x 10^-12 erg s^-1 cm^-2 deg^-2, a level less than 20% of the cosmic X-ray background brightness. We trace the run of temperature with radius at r > 0.4 Mpc and find that it falls relatively rapidly (T ~ r^-0.9), reaching a value about one third of its peak at the largest radius we can measure it. Assuming the intracluster medium is in hydrostatic equilibrium and is polytropic, we find a polytropic index of 1.3 +0.3-0.2 and we estimate a mass of 4.1 +0.5-0.3 x 10^14 M_solar within 1.3 Mpc, somewhat (2.7-sigma) lower than that reported by previous observers. However, our observations provide evidence for departure from hydrostatic equilibrium at radii as small as r ~ 1.3 Mpc ~ r_500 in this apparently regular and symmetrical cluster.
Clumping and turbulence are expected to affect the matter accreted onto the outskirts of galaxy clusters. To determine their impact on the thermodynamic properties of Abell 2142 we perform an analysis of the X-ray temperature data from XMM-Newton via our SuperModel, a state-of-the-art tool for investigating the astrophysics of the intracluster medium already tested on many individual clusters (since Cavaliere et al. 2009). Using the gas density profile corrected for clumpiness derived by Tchernin et al. (2016), we find evidence for the presence of a nonthermal pressure component required to sustain gravity in the cluster outskirts of Abell 2142, that amounts to about 30% of the total pressure at the virial radius. The presence of the nonthermal component implies the gas fraction to be consistent with the universal value at the virial radius and the electron thermal pressure profile to be in good agreement with that inferred from the SZ data. Our results indicate that the presence of gas clumping and of a nonthermal pressure component are both necessary to recover the observed physical properties in the cluster outskirts. Moreover, we stress that an alternative method often exploited in the literature (included Abell 2142) to determine the temperature profile k_BT = P_e/n_e basing on a combination of the Sunyaev-Zeldovich (SZ) pressure P_e and of the X-ray electron density n_e does not allow to highlight the presence of nonthermal pressure support in the cluster outskirts.
We present Herschel/PACS, MMT/Hectospec and XMM-Newton observations of Abell 1835, one of the brightest X-ray clusters on the sky, and the host of a strong cool core. Even though Abell 1835 has a prototypically relaxed X-ray morphology and no signs of ongoing merger activity in strong- and weak-lensing mass maps, it has a complex velocity distribution, suggesting that it is still accreting significant amounts of mass in the form of smaller satellite systems. Indeed, we find strong dynamical segregation of star-forming dusty galaxies from the optically selected cluster population. Most Herschel sources are found close to the virial radius of the cluster, and almost a third appear to be embedded within a filament feeding the cluster from the SW. We find that the most luminous infrared galaxies are likely involved in galaxy-galaxy interactions that may have triggered the current phase of star formation.
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