科研之友
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摘要
We present the results from extensive, new observations of the Perseus Cluster of galaxies, obtained as a Suzaku Key Project. The 85 pointings analysed span eight azimuthal directions out to 2 degrees = 2.6 Mpc, to and beyond the virial radius r(200) similar to 1.8 Mpc, offering the most detailed X-ray measurements 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-fitting power-law index delta = 1.69 +/- 0.13, significantly smaller than expected from numerical simulations. The entropy profile in the outskirts lies systematically below the power-law behaviour expected from large-scale structure formation models which include only the heating associated with gravitational collapse. Conversely, the pressure profile beyond similar to 0.6r(200) shows an excess with respect to the best-fitting model describing the SZ measurements for a sample of clusters observed with the Planck satellite. The differences between the expected and measured density, entropy and pressure profiles can be explained by a systematic overestimation of the ICM density at large radii caused by homogeneous modelling of inhomogeneous gas distributions (i.e. gas clumping), with the density overestimates ranging from factors of similar to 1.2 to 2 or more at r(200) along different directions. We find no evidence for a bias in the temperature measurements within the virial radius. Along the cluster minor axis, we find a flattening of the entropy profiles outside similar to 0.6r(200), while along the major axis, the entropy rises all the way to the outskirts.
- 出版日期2014-2
