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141.
Yasuhiro Hashimoto J. Patrick Henry Hans Böhringer 《Monthly notices of the Royal Astronomical Society》2007,380(2):835-838
We investigated the influence of environment on cluster morphology by examining the alignment of the cluster position angle with respect to the nearest neighbour cluster. The cluster position angle and ellipticity were measured using high spatial resolution X-ray data taken from the Chandra archive, while the nearest neighbour sample was extracted from the Abell cluster catalogue. We found high confidence for an alignment when neighbour distance (Dn) was less than 70 h −1 Mpc, while we found no significant variations of the confidence level at various values of Dn less than 70 h −1 Mpc. 相似文献
142.
N. A. Tikhonov 《Astronomy Letters》2007,33(3):137-148
Archival Hubble Space Telescope (HST) data have been used for the photometry of stars in blue compact dwarf (BCD) galaxies of the IZw18 system. Applying the spatial selection of stars, we have detected red giants, stars older than 1–2 Gyr, in the galaxies. These red giants have allowed the distance to IZw18 to be reliably determined for the first time: D = 13.9 ± 1.2 Mpc. The presence of old stars in the galaxies of the IZw18 system refutes the hypothesis about the observed primary star formation in these galaxies. 相似文献
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We study the effect of contamination by interlopers in kinematic samples of galaxy clusters. We demonstrate that without the proper removal of interlopers the inferred parameters of the mass distribution in the cluster are strongly biased towards higher mass and lower concentration. The interlopers are removed using two procedures previously shown to work most efficiently on simulated data. One is based on using the virial mass estimator and calculating the maximum velocity available to cluster members and the other relies on the ratio of the virial and projected mass estimators. We illustrate the performance of the methods in detail using the example of A576, a cluster with a strong uniform background contamination, and compare the case of A576 to 15 other clusters with different degree of contamination. We model the velocity dispersion and kurtosis profiles obtained for the cleaned data samples of these clusters solving the Jeans equations to estimate the mass, concentration and anisotropy parameter. We present the mass–concentration relation for the total sample of 22 clusters. 相似文献
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We investigate the possibility of explaining the observed ripples in the X-ray gas in the Perseus and Virgo clusters through
natural oscillations of a perturbed radio cocoon. Such a perturbation would result from an expanding overpressured cocoon
of radio plasma overshooting its pressure equilibrium point with the cluster gas. The oscillations are heavily acoustically
damped, and energy injection rates required to sustain them are consistent with observed AGN powers. Viscous dissipation of
sound waves generated by these oscillations heats the cluster gas. By comparing our model with observations in Perseus and
Virgo, we reproduce the observed ripple separations and amplitudes. Spitzer viscosity is largely sufficient in explaining
the gas density profile, suggesting that thermal conductivity is likely to be heavily suppressed. In the central regions,
viscous heating can suppress cooling flows on timescales exceeding the radio source lifetime. 相似文献
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