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Register a new userCool core disturbed: Observational evidence for coexistence of sub-sonic sloshing gas and stripped shock-heated gas around the core of RX J1347.5-1145
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RXJ1347.5-1145 (z = 0.451) is one of the most luminous X-ray galaxy clusters, which hosts a prominent cool core and exhibits a signature of a major merger. We present the first direct observational evidence for sub-sonic nature of sloshing motion of the cool core. We find that a residual X-ray image from the Chandra X-ray Observatory after removing the global emission shows a clear dipolar pattern characteristic of gas sloshing, whereas we find no significant residual in the Sunyaev-Zeldovich effect (SZE) image from the Atacama Large Millimeter/submillimeter Array (ALMA). We estimate the equation of state of perturbations in the gas from the X-ray and SZE residual images. The inferred velocity is 420 +310 -420 km s-1, which is much lower than the adiabatic sound speed of the intracluster medium in the core. We thus conclude that the perturbation is nearly isobaric, and gas sloshing motion is consistent with being in pressure equilibrium. Next, we report evidence for gas stripping of an infalling subcluster, which likely shock-heats gas to high temperature well in excess of 20 keV. Using mass distribution inferred from strong lensing images of the Hubble Space Telescope (HST), we find that the mass peak is located away from the peak position of stripped gas with statistical significance of > 5{sigma}. Unlike for the gas sloshing, the velocity inferred from the equation of state of the excess hot gas is comparable to the adiabatic sound speed expected for the 20 keV intracluster medium. All of the results support that the southeast substructure is created by a merger. On the other hand, the positional offset between the mass and the gas limits the self-interaction cross section of dark matter to be less than 3.7 h-1 cm2 g-1 (95% CL).
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We present line-of-sight gas sloshing first found in a cool core in a galaxy cluster. The galaxy cluster Abell 907 is identified as a relaxed cluster owing to its global X-ray surface brightness taken by the Chandra X-ray Observatory. The X-ray residual image after removing the global emission of the intracluster medium (ICM), however, shows an arc-like positive excess and a negative excess surrounding the central positive excess in the cluster core, which in turn indicates a disturbance of the ICM. We analyze the X-ray spectra extracted from both regions and find that (1) the ICM temperature and the metal abundance in the positive excess are lower and higher than those in the negative excess, respectively, and (2) the ICM is nearly in pressure equilibrium. We also find a slight redshift difference between the positive and the negative excesses, which corresponds to the velocity shear of $1680^{+1300}_{-920}$ km s$^{-1}$ ($1sigma$). The X-ray residual image and the ICM properties are consistent with those expected by line-of-sight gas sloshing. Assuming that the gas is moving toward inverse-parallel to each other along the line-of-sight, the shear velocity is expected to be $sim 800$ km s$^{-1}$. The velocity field of this level is able to provide non-thermal pressure support by $sim 34%$ relative to the thermal one. The total kinetic energy inferred from the shear velocity corresponds to $sim 30%$ of the bolometric luminosity of the sloshing ICM. Abell 907 is therefore complementary to galaxy clusters in which gas sloshing takes place in the plane of the sky, and is important for understanding gas dynamics driven by sloshing and its influence on the heating to prevent runaway cooling.
We present an analysis of a 72 ks Chandra observation of the double cluster Abell 1644 (z=0.047). The X-ray temperatures indicate the masses are M500=2.6+/-0.4 x10^{14} h^{-1} M_sun for the northern subcluster and M500=3.1+/-0.4 x10^{14} h^{-1} M_sun for the southern, main cluster. We identify a sharp edge in the radial X-ray surface brightness of the main cluster, which we find to be a cold front, with a jump in temperature of a factor of ~3. This edge possesses a spiral morphology characteristic of core gas sloshing around the cluster potential minimum. We present observational evidence, supported by hydrodynamic simulations, that the northern subcluster is the object which initiated the core gas sloshing in the main cluster at least 700 Myr ago. We discuss reheating of the main clusters core gas via two mechanisms brought about by the sloshing gas: first, the release of gravitational potential energy gained by the cores displacement from the potential minimum, and second, a dredging inwards of the outer, higher entropy cluster gas along finger-shaped streams. We find the available gravitational potential energy is small compared to the energy released by the cooling gas in the core.
We present a revised strong lensing mass reconstruction of the galaxy cluster RX J1347.5-1145. The X-ray luminous cluster at redshift z=0.451 has already been studied intensively in the past. Based on information of two such previous (strong-)lensing studies by Halkola et al. (2008) and Bradac et al. (2008), as well as by incorporating newly available data from the Cluster Lensing And Supernovae survey with Hubble (CLASH, Postman et al. 2012), we identified four systems of multiply lensed images (anew) in the redshift range 1.75 <= z <= 4.19. One multiple image system consists of in total eight multiply lensed images of the same source. The analysis based on a parametric mass model derived with the software glafic (Oguri 2010) suggests that the high image multiplicity is due to the source (z_phot = 4.19) being located on a so-called swallowtail caustic. In addition to the parametric mass model, we also employed a non-parametric approach using the software PixeLens (Saha and Williams 1997, 2004) in order to reconstruct the projected mass of the cluster using the same strong lensing data input. Both reconstructed mass models agree in revealing several mass components and a highly elliptic shape of the mass distribution. Furthermore, the projected mass inside, for example, a radius R ~35 arcsec ~200 kpc of the cluster for a source at redshift z=1.75 obtained with PixeLens exceeds the glafic estimate within the same radius by about 13 per cent. The difference could be related to the fundamental degeneracy involved when constraining dark matter substructures with gravitationally lensed arcs.
We present the results from the analysis of long Suzaku observations of the most X-ray luminous galaxy cluster RX J1347.5-1145 at z=0.451. Aims: We study physical properties of the hot (~20 keV) gas clump in the south-east (SE) region discovered by the Sunyaev-Zeldovich (SZ) effect observations, to understand the gas physics of a violent cluster merger. We also explore a signature of non-thermal emission using the hard X-ray data. Results: We find that the single-temperature model fails to reproduce the continuum emission and Fe-K lines measured by XIS simultaneously. The two-temperature model with a very hot component improves the fit, although the XIS data can only give a lower bound on its temperature. We detect the hard X-ray emission in the 12-40 keV band at the 7 sigma level; however, the significance becomes marginal when the systematic error in the background estimation is included. With the Suzaku + Chandra joint analysis, we determine the temperature of the SE excess component to be 25.3^{+6.1}_{-4.5} ^{+6.9}_{-9.5} keV (90% statistical and systematic errors), which is in an excellent agreement with the previous SZ + X-ray analysis. This is the first time that the X-ray spectroscopy alone gives a good measurement of the temperature of the hot component in the SE region, which is made possible by Suzakus unprecedented sensitivity to the wide X-ray band. These results strongly indicate that the cluster has undergone a recent, violent merger. The spectral analysis shows that the SE component is consistent with being thermal. We find the 3 sigma upper limit on the non-thermal flux, F < 8e-12 erg s^{-1} cm^{-2} in the 12-60 keV band. Combining this limit with a recent discovery of the radio mini halo at 1.4 GHz, we find a lower limit on the strength of the intracluster magnetic field, B > 0.007 micro G.
The cluster RX J1347.5-1145, the most luminous cluster in the X-ray wavelengths, was imaged with the newly installed Space Telescope Imaging Spectrograph (STIS) on-board HST. Its relatively high redshift (0.451) and luminosity indicate that this is one of the most massive of all known clusters. The STIS images unambiguously show several arcs in the cluster. The largest two arcs (> 5 arcsec in length) are symmetrically situated on opposite sides of the cluster, at a distance of ~ 35 arcsec from the central galaxy. The STIS images also show approximately 100 faint galaxies within the radius of the arcs whose combined luminosity is ~ 4 x 10^11 Lsun. We also present ground-based spectroscopic observations of the northern arc which show one clear emission line at 6730 A, which is consistent with an identification as [OII] 3727 A, implying a redshift of 0.81 for this arc. The southern arc shows a faint continuum but no emission features. The surface mass within the radius of the arcs (240 kpc), as derived from the gravitational lensing, is 6.3 x 10^14 Msun. The resultant mass-to-light ratio of ~1200 is higher than what is seen in many clusters but smaller than the value recently derived for some `dark X-ray clusters (Hattori et al. 1997). The total surface mass derived from the X-ray flux within the radius of the arcs is ~2.1 - 6.8 x 10^14 Msun, which implies that the ratio of the gravitational to the X-ray mass is ~1 to 3. The surface GAS mass within this radius is ~3.5 x 10^13 Msun, which implies that at least 6% of the total mass within this region is baryonic.
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