Ota et al. 2007
http://adsabs.harvard.edu/abs/2007PASJ...59S.351O
The Centaurus cluster (z=0.0104) was observed with the X-ray Imaging Spectrometer (XIS) onboard the Suzaku X-ray satellite in three pointings, one centered on the cluster core and the other two offset by ±8' in declination. To search for possible bulk motions of the intracluster medium, the central energy of a He-like Fe K line (at a rest-frame energy of 6.7keV) was examined to look for a positional dependence. Over spatial scales of 50kpc to 140kpc around the cluster core, the central line energy was found to be constant within a calibration error of 15eV. The 90% upper limit on the line-of-sight velocity difference is |Δv| < 1400 km s-1, giving a tighter constraint than previous measurements. The significant velocity gradients inferred from a previous Chandra study were not detected between two pairs of rectangular regions near the cluster core. These results suggest that the bulk velocity does not largely exceed the thermal velocity of the gas in the central region of the Centaurus cluster. The mean redshift of the intracluster medium was determined to be 0.0097, in agreement with the optical redshift of the cluster within the calibration uncertainty. Implications of the present results for estimating the cluster mass are briefly discussed.
2007/01/01
2006/11/22
A very deep Chandra observation of the Perseus cluster: shocks, ripples and conduction
MNRAS, 2006
We present the first results from a very deep Chandra X-ray observation of the core of the Perseus cluster of galaxies. A pressure map reveals a clear thick band of high pressure around the inner radio bubbles. The gas in the band must be expanding outwards and the sharp front to it is identified as a shock front, yet we see no temperature jump across it; indeed, there is more soft emission behind the shock than in front of it. We conclude that in this inner region either thermal conduction operates efficiently or the co-existing relativistic plasma seen as the radio mini-halo is mediating the shock. If common, isothermal shocks in cluster cores mean that we cannot diagnose the expansion speed of radio bubbles from temperature measurements alone. They can at times expand more rapidly than currently assumed without producing significant regions of hot gas. Bubbles may also be significantly more energetic. The pressure ripples found in earlier images are identified as isothermal sound waves. A simple estimate based on their amplitude confirms that they can be an effective distributed heat source able to balance radiative cooling. We see multiphase gas with about 109Msolar at a temperature of about 0.5 keV. Much, but not all, of this X-ray emitting cooler gas is spatially associated with the optical filamentary nebula around the central galaxy, NGC1275. A residual cooling flow of about 50Msolaryr-1 may be taking place. A channel is found in the pressure map along the path of the bubbles, with indications found of outer bubbles. The channel connects in the south (S) with a curious cold front.
We present the first results from a very deep Chandra X-ray observation of the core of the Perseus cluster of galaxies. A pressure map reveals a clear thick band of high pressure around the inner radio bubbles. The gas in the band must be expanding outwards and the sharp front to it is identified as a shock front, yet we see no temperature jump across it; indeed, there is more soft emission behind the shock than in front of it. We conclude that in this inner region either thermal conduction operates efficiently or the co-existing relativistic plasma seen as the radio mini-halo is mediating the shock. If common, isothermal shocks in cluster cores mean that we cannot diagnose the expansion speed of radio bubbles from temperature measurements alone. They can at times expand more rapidly than currently assumed without producing significant regions of hot gas. Bubbles may also be significantly more energetic. The pressure ripples found in earlier images are identified as isothermal sound waves. A simple estimate based on their amplitude confirms that they can be an effective distributed heat source able to balance radiative cooling. We see multiphase gas with about 109Msolar at a temperature of about 0.5 keV. Much, but not all, of this X-ray emitting cooler gas is spatially associated with the optical filamentary nebula around the central galaxy, NGC1275. A residual cooling flow of about 50Msolaryr-1 may be taking place. A channel is found in the pressure map along the path of the bubbles, with indications found of outer bubbles. The channel connects in the south (S) with a curious cold front.
2005/09/01
2004/12/25
ASCA Compilation of X-Ray Properties of Hot Gas in Elliptical Galaxies and Galaxy Clusters: Two Breaks in the Temperature Dependences
Fukazawa, Makishima, Ohashi
http://adsabs.harvard.edu/abs/2004PASJ...56..965F
Utilizing ASCA archival data of about 300 objects of elliptical galaxies, groups, and clusters of galaxies, we performed systematic measurements of the X-ray properties of hot gas in their systems, and compiled them in this paper. The steepness of the luminosity-temperature (LT) relation, LiX ∝ (kT)α, in the range of kT ˜ 1.5 ‑ 15 keV is α = 3.17 ± 0.15, consistent with previous measurements. In the relation, we find two breaks at around ICM temperatures of 1 keV and 4 keV: α = 2.34 ± 0.29 above 4 keV, 3.74 ± 0.32 in 1.5-5 keV, and 4.03 ± 1.07 below 1.5keV. Such two breaks are also evident in the temperature and size relation. The steepness in the LT relation at kT > 4 keV is consistent with the scale-relation derived from the CDM model, indicating that the gravitational effect is dominant in richer clusters, while poorer clusters suffer non-gravity effects. The steep LT relation below 1keV is almost attributed to X-ray faint systems of elliptical galaxies and galaxy groups. We found that the ICM mass within the scaling radius R1500 follows the relation of Mgas ∝ T2.33±0.07 from X-ray faint galaxies to rich clusters. Therefore, we speculate that even such X-ray faint systems contain a large-scale hot gas, which is too faint to detect.
http://adsabs.harvard.edu/abs/2004PASJ...56..965F
Utilizing ASCA archival data of about 300 objects of elliptical galaxies, groups, and clusters of galaxies, we performed systematic measurements of the X-ray properties of hot gas in their systems, and compiled them in this paper. The steepness of the luminosity-temperature (LT) relation, LiX ∝ (kT)α, in the range of kT ˜ 1.5 ‑ 15 keV is α = 3.17 ± 0.15, consistent with previous measurements. In the relation, we find two breaks at around ICM temperatures of 1 keV and 4 keV: α = 2.34 ± 0.29 above 4 keV, 3.74 ± 0.32 in 1.5-5 keV, and 4.03 ± 1.07 below 1.5keV. Such two breaks are also evident in the temperature and size relation. The steepness in the LT relation at kT > 4 keV is consistent with the scale-relation derived from the CDM model, indicating that the gravitational effect is dominant in richer clusters, while poorer clusters suffer non-gravity effects. The steep LT relation below 1keV is almost attributed to X-ray faint systems of elliptical galaxies and galaxy groups. We found that the ICM mass within the scaling radius R1500 follows the relation of Mgas ∝ T2.33±0.07 from X-ray faint galaxies to rich clusters. Therefore, we speculate that even such X-ray faint systems contain a large-scale hot gas, which is too faint to detect.
2004/01/01
Wide-Field X-Ray Temperature, Pressure, and Entropy Maps of A754
Henry et al. 2004
copy from http://adsabs.harvard.edu/abs/2004ApJ...615..181H
We present a mosaic of XMM-Newton observations of the nearby major-merger cluster A754 that has either a wider field or better spectral or spatial resolution than previous observations. We construct maps of X-ray surface brightness and temperature integrated along the line of sight. From these two primary maps we derive pseudopressure and pseudoentropy maps. There is structure on a large range of scales in these maps, but the basic pattern is similar to numerical hydrodynamic simulations of cluster mergers. The high surface brightness eastern bar contains gas with the minimum entropy and temperature coupled with the highest iron abundance and density in the cluster. A new feature revealed by these observations is a plumelike structure that appears to emerge from the bar heading northwest. The diffuse radio source also occupies this region, and there is some correspondence between the two. Another new feature is a rim of hot gas to the east, south, and west. We interpret the bar as the core gas from the original main cluster flattened and displaced from the dark matter potential minimum by the merger. The hot rim is the outgoing forward shock from the merger. However, this and previous shocks were weak (M<=2.25), so they are likely only small contributors to the radio-emitting particles. These observations lend support to the merger hypothesis in A754, but some of the parameters of existing models need modification.
Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).
copy from http://adsabs.harvard.edu/abs/2004ApJ...615..181H
We present a mosaic of XMM-Newton observations of the nearby major-merger cluster A754 that has either a wider field or better spectral or spatial resolution than previous observations. We construct maps of X-ray surface brightness and temperature integrated along the line of sight. From these two primary maps we derive pseudopressure and pseudoentropy maps. There is structure on a large range of scales in these maps, but the basic pattern is similar to numerical hydrodynamic simulations of cluster mergers. The high surface brightness eastern bar contains gas with the minimum entropy and temperature coupled with the highest iron abundance and density in the cluster. A new feature revealed by these observations is a plumelike structure that appears to emerge from the bar heading northwest. The diffuse radio source also occupies this region, and there is some correspondence between the two. Another new feature is a rim of hot gas to the east, south, and west. We interpret the bar as the core gas from the original main cluster flattened and displaced from the dark matter potential minimum by the merger. The hot rim is the outgoing forward shock from the merger. However, this and previous shocks were weak (M<=2.25), so they are likely only small contributors to the radio-emitting particles. These observations lend support to the merger hypothesis in A754, but some of the parameters of existing models need modification.
Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).
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