Discovery of Gas Bulk Motion in the Galaxy Cluster Abell 2256 with Suzaku

The results from Suzaku observations of the galaxy cluster Abell2256 are presented. This cluster is a prototypical and well-studied merging system, exhibiting substructures both in the X-ray surface brightness and in the radial velocity distribution of member galaxies. There are main and sub components separating by 3'.5 in the sky and by about 2000 km s$^{-1}$ in radial velocity peaks of member galaxies. In order to measure Doppler shifts of iron K-shell lines from the two gas components by the Suzaku XIS, the energy scale of the instrument was evaluated carefully and found to be calibrated well. A significant shift of the radial velocity of the sub component gas with respect to that of the main cluster was detected. All three XIS sensors show the shift independently and consistently among the three. The difference is found to be 1500 $\pm 300$ (statistical) $\pm 300$ (systematic) km s$^{-1}$. The X-ray determined absolute redshifts of and hence the difference between the main and sub components are consistent with those of member galaxies in optical. The observation indicates robustly that the X-ray emitting gas is moving together with galaxies as a substructure within the cluster. These results along with other X-ray observations of gas bulk motions in merging clusters are discussed.Comment: Accepted for publication in PASJ in 2011-03-2

The relation between the cool-core radius and the host galaxy clusters: thermodynamic properties and cluster mass

We present a detailed study of cool-core systems in a sample of four galaxy clusters (RXCJ1504.1-0248, A3112, A4059, and A478) using archival X-ray data from the Chandra X-ray Observatory. Cool cores are frequently observed at the centers of galaxy clusters and are considered to be formed by radiative cooling of the intracluster medium (ICM). Cool cores are characterized by a significant drop in the ICM temperature toward the cluster center. We extract and analyze X-ray spectra of the ICM to measure the radial profiles of the ICM thermodynamic properties including temperature, density, pressure, entropy, and radiative cooling time. We define the cool-core radius as the turnover radius in the ICM temperature profile and investigate the relation between the cool-core radius and the properties of the host galaxy clusters. In our sample, we observe that the radiative cooling time of the ICM at the cool-core radius exceeds 10\,Gyr, with RXCJ1504.1-0248 exhibiting a radiative cooling time of $32^{+5}_{-11}$\,Gyr at its cool-core radius. These results indicate that not only radiative cooling but also additional mechanisms such as gas sloshing may play an important role in determining the size of cool cores. Additionally, we find that the best-fit relation between the cool-core radius and the cluster mass ($M_{500}$) is consistent with a linear relation. Our findings suggest that cool cores are linked to the evolution of their host galaxy clusters.Comment: 22 pages, 10 figures, 10 tables, submitted to Ap

The Dynamical State of the Frontier Fields Galaxy Cluster Abell 370

We study the dynamics of Abell 370 (A370), a highly massive Hubble Frontier Fields galaxy cluster, using self-consistent three-dimensional N-body/hydrodynamical simulations. Our simulations are constrained by X-ray, optical spectroscopic and gravitational lensing, and Sunyaev-Zel'dovich (SZ) effect observations. Analyzing archival Chandra observations of A370 and comparing the X-ray morphology to the latest gravitational lensing mass reconstruction, we find offsets of ∼30 and ∼100 kpc between the two X-ray surface brightness peaks and their nearest mass surface density peaks, suggesting that it is a merging system, in agreement with previous studies. Based on our dedicated binary cluster merger simulations, we find that initial conditions of the two progenitors with virial masses of $1.7\\times {10}^{15}$ and $1.6\\times {10}^{15}\\,{M}_{\\odot }$ , an infall velocity of 3500 km s-1, and an impact parameter of 100 kpc can explain the positions and the offsets between the peaks of the X-ray emission and mass surface density, the amplitude of the integrated SZ signal, and the observed relative line-of-sight velocity. Moreover, our best model reproduces the observed velocity dispersion of cluster member galaxies, which supports the large total mass of A370 derived from weak lensing. Our simulations strongly suggest that A370 is a post major merger after the second core passage in the infalling phase, just before the third core passage. In this phase, the gas has not settled down in the gravitational potential well of the cluster, which explains why A370 does not follow closely the galaxy cluster scaling relations

Performance of a newly developed SDCCD for X-ray use

A Scintillator Deposited CCD (SDCCD) is a wide-band X-ray detector consisting of a CCD and a scintillator directly attached to each other. We assembled the newly developed SDCCD that the scintillator CsI(Tl) is below the fully depleted CCD. The incident X-rays enter the CCD depletion layer first. Then, X-rays passing through the depletion layer are absorbed in the CsI(Tl). The contact surface of the CCD is a back-illuminated side so that we can have good light collection efficiency. In our experimental setup, we confirmed good performance of our SDCCD detecting many emission lines up to 88\,keV that comes from $^{109}$Cd.Comment: 4 pages, 6 figures, accepted publication for Nucl. Instr. and Meth. (2010

Gas Density Perturbations in Cool Cores of CLASH Galaxy Clusters

We present a systematic study of gas density perturbations in cool cores of high-mass galaxy clusters. We select 12 relaxed clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) sample and analyze their cool core features observed with the Chandra X-ray Observatory. We focus on the X-ray residual image characteristics after subtracting their global profile of the X-ray surface brightness distribution. We find that all the galaxy clusters in our sample have, at least, both one positive and one negative excess regions in the X-ray residual image, indicating the presence of gas density perturbations. We identify and characterize the locally perturbed regions using our detection algorithm, and extract X-ray spectra of the intracluster medium (ICM). The ICM temperature in the positive excess region is lower than that in the negative excess region, whereas the ICM in both regions is in pressure equilibrium in a systematic manner. These results indicate that gas sloshing in cool cores takes place in more than 80% of relaxed clusters (95% CL). We confirm this physical picture by analyzing synthetic X-ray observations of a cool-core cluster from a hydrodynamic simulation, finding that our detection algorithm can accurately extract both the positive and negative excess regions and can reproduce the temperature difference between them. Our findings support the picture that the gas density perturbations are induced by gas sloshing, and a large fraction of cool-core clusters have undergone gas sloshing, indicating that gas sloshing may be capable of suppressing runaway cooling of the ICM.Comment: 30 pages, 8 figures, accepted for publication in Ap