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Astron. Astrophys. 348, 711-727 (1999)

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Regularity in the X-ray surface brightness profiles of galaxy clusters and the M-T relation

D.M. Neumann and M. Arnaud

CEA/DSM/DAPNIA/Service d'Astrophysique, CEA-Saclay, L'Orme des Merisiers, Bât. 709, F-91191 Gif-sur-Yvette, France (ddon@cea.fr; arnaud@hep.saclay.cea.fr)

Received 7 January 1999 / Accepted 28 June 1999


We used archival ROSAT observations to investigate the X-ray surface brightness profiles of a sample of 26 clusters in the redshift range [FORMULA]. For 15 of these clusters accurate temperatures (k[FORMULA] keV) were available from the literature. The scaled emission measure profiles look remarkably similar above [FORMULA] times the virial radius ([FORMULA]). On the other hand a large scatter is observed in the cluster core properties. We fitted a [FORMULA]-model (with and without excising the central part) to all the ROSAT profiles to quantify the structural variations in the cluster population, unraveling a robust quadratic correlation between the core radius and the slope parameter [FORMULA]. We quantified the shape of each gas density profile by the variation with radius of the logarithmic slope, [FORMULA]. The bi-weight dispersion of [FORMULA] among the clusters is less than [FORMULA] for any given scaled radii above [FORMULA]. There is a clear minimum spread at [FORMULA], which is related to the existence of a correlation between core radius and [FORMULA]. These ensemble properties are insensitive to the exact treatment of a possible central excess when fitting the profiles. On the other hand the scatter in [FORMULA] is decreased when the radii are scaled to [FORMULA].

The regularity we found in the gas profiles at [FORMULA] supports the existence of a universal underlying dark matter profile, as already predicted by theoretical works. It suggests that non gravitational heating is negligible for clusters with temperature above [FORMULA] keV. Our results are consistent with the classical scaling relation between Mass and Temperature ([FORMULA]). Accordingly the spread in the scaled mass profiles derived from the hydrostatic isothermal [FORMULA]-model is small. The very large scatter observed in the core properties favor scenario where Cooling Flows are periodically erased by merger events.

Key words: galaxies: clusters: general – cosmology: observations – cosmology: dark matter – X-rays: galaxies

Send offprint requests to: D.M. Neumann

© European Southern Observatory (ESO) 1999

Online publication: August 13, 199