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Register a new userInhomogeneity in the Hot Intracluster Medium of Abell 1060 Observed with Chandra
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A Chandra observation of the non-cooling flow cluster A 1060 has confirmed that the hot intracluster medium has fairly uniform distributions of temperature and metal abundance from a radius of about 230 kpc to the central 5 kpc region (H_0= 75 km/s/Mpc). The radial temperature profile shows a broad peak at 30-40 kpc from the center at a level ~20% higher than that in the outer region. Assuming spatially uniform temperature and abundance distributions, we derived a 3-dimensional density structure by iteratively correcting the beta model, and obtained the central gas density to be 8.2^{+1.8}_{-1.0} x 10^{-3} cm^{-3}. The distribution of gravitational mass was estimated from the density profile, and a central concentration of mass within a radius of 50 kpc was indicated. The data also suggest several high-abundance regions. The most significant blob adjacent to the central galaxy NGC 3311 has a radius of about 9 kpc, which indicates a metallicity of ~1.5 solar. We consider that this blob may be produced by the gas stripped off from NGC 3311.
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Hubble Space Telescope photometry from the ACS/WFC and WFPC2 cameras is used to detect and measure globular clusters (GCs) in the central region of the rich Perseus cluster of galaxies. A detectable population of Intragalactic GCs is found extending out to at least 500 kpc from the cluster center. These objects display luminosity and color (metallicity) distributions that are entirely normal for GC populations. Extrapolating from the limited spatial coverage of the HST fields, we estimate very roughly that the entire Perseus cluster should contain ~50000 or more IGCs, but a targetted wide-field survey will be needed for a more definitive answer. Separate brief results are presented for the rich GC systems in NGC 1272 and NGC 1275, the two largest Perseus ellipticals. For NGC 1272 we find a specific frequency S_N = 8, while for the central giant NGC 1275, S_N ~ 12. In both these giant galaxies, the GC colors are well matched by bimodal distributions, with the majority in the blue (metal-poor) component. This preliminary study suggests that Perseus is a prime target for a more comprehensive deep imaging survey of Intragalactic GCs.
XMM-Newton observations of 19 galaxy clusters are used to measure the elemental abundances and their spatial distributions in the intracluster medium. The sample mainly consists of X-ray bright and relaxed clusters with a cD galaxy. Along with detailed Si, S and Fe radial abundance distributions within 300-700 kpc in radius, the O abundances are accurately derived in the central region of the clusters. The Fe abundance maxima towards the cluster center, possibly due to the metals from the cD galaxy,are spatially resolved. The Si and S abundances also exhibit central increases in general, resulting in uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in general uniform over the cluster. The mean O to Fe ratio within the cluster core is sub-solar, while that of the cluster scale is larger than the solar ratio. These measurements indicate that most of the Fe-Si-S and O in the intracluster medium have different origins, presumably in supernovae Ia and II, respectively. The obtained Fe and O mass are also used to discuss the past star formation history in clusters.
The rich galaxy cluster Abell 2204 exhibits edges in its X-ray surface brightness at $sim 65$ and $35 {rm~ kpc}$ west and east of its center, respectively. The presence of these edges, which were interpreted as sloshing cold fronts, implies that the intracluster medium was recently disturbed. We analyze the properties of the intracluster medium using multiple Chandra observations of Abell 2204. We find a density ratio $n_{rm in}/n_{rm out} = 2.05pm0.05$ and a temperature ratio $T_{rm out}/T_{rm in} = 1.91pm0.27$ (projected, or $1.87pm0.56$ deprojected) across the western edge, and correspondingly $n_{rm in}/n_{rm out} = 1.96pm0.05$ and $T_{rm out}/T_{rm in} =1.45pm0.15$ (projected, or $1.25pm0.26$ deprojected) across the eastern edge. These values are typical of cold fronts in galaxy clusters. This, together with the spiral pattern observed in the cluster core, supports the sloshing scenario for Abell 2204. No Kelvin-Helmholtz eddies are observed along the cold front surfaces, indicating that they are effectively suppressed by some physical mechanism. We argue that the suppression is likely facilitated by the magnetic fields amplified in the sloshing motion, and deduce from the measured gas properties that the magnetic field strength should be greater than $24pm6$ $mu$G and $32pm8$ $mu$G along the west and east cold fronts, respectively.
The radio lobes of Hydra A lie within cavities surrounded by a rim of enhanced X-ray emission in the intracluster gas. Although the bright rim appears cooler than the surrounding gas, existing Chandra data do not exclude the possibility that the rim is produced by a weak shock. A temperature map shows that cool gas extends out along the radio axis of Hydra A. The age of the radio source and equipartition pressure of the radio lobe argue against a shock, and comparison with similar structure in the Perseus Cluster also suggests that the rim is cool. We show that the cool bright rim cannot be the result of shock induced cooling, or due to the effect of magnetic fields in shocks. The most likely source of low entropy (cool) gas is entrainment by the rising cavity. This requires some means of communicating the bouyant force on the cavity to the surrounding gas. The magnetic field required to produce the Faraday rotation in Hydra A has the appropriate properties for this, if the Faraday screen is mainly in this bright rim. In Hydra A, the mass outflow due to the rising cavities could be sufficient to balance cooling driven inflow, so preventing the build up of low entropy gas in the cluster core.
Chandra ACIS-S observations of the galaxy cluster A3112 feature the presence of an excess of X-ray emission above the contribution from the diffuse hot gas, which can be equally well modeled with an additional non-thermal power-law model or with a low-temperature thermal model of low metal abundance. We show that the excess emission cannot be due to uncertainties in the background subtraction or in the Galactic HI column density. Calibration uncertainties in the ACIS detector that may affect our results are addressed by comparing the Chandra data to XMM MOS and PN spectra. While differences between the three instruments remain, all detect the excess in similar amounts, providing evidence against an instrumental nature of the excess. Given the presence of non-thermal radio emission near the center of A3112, we argue that the excess X-ray emission is of non-thermal nature and distributed throughout the entire X-ray bandpass, from soft to hard X-rays. The excess can be explained with the presence of a population of relativistic electrons with ~7% of the clusters gas pressure. We also discuss a possible thermal nature of the excess, and examine the problems associated with such interpretation.
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