Fakultäten » Mathematisch-naturwissenschaftliche Fakultät » Physik-Institut » Prof. Dr. Philippe Jetzer » Piffaretti

Completed research project

Title / Titel XMM-Newton observations of the temperature structure of the central gas in cooling clusters
PDF Abstract (PDF, 14 KB)
Summary / Zusammenfassung We present spatially resolved X-ray spectra taken with the EPIC cameras of XMM-Newton of a sample of 17 cooling clusters and three non-cooling clusters for comparison. The deprojected spectra are analyzed with a multi-temperature model, independent of any a priori assumptions about the physics behind the cooling and heating mechanisms. All cooling clusters show a central decrement of the average temperature, most of them of a factor of ~2. Three clusters only show a weak temperature decrement, while two others have a very strong temperature decrement. At each radius within the cooling region the gas is not isothermal. The differential emission measure distribution shows a strong peak near the maximum (ambient) temperature, with a steep decline towards lower temperatures, approximately proportional to T3, or alternatively a cut-off at about a quarter to half of the maximum temperature. In general, we find a poor correlation between radio flux of the central galaxy and the temperature decrement of the cooling flow. This is interpreted as evidence that except for a few cases (like the Hydra A cluster) heating by a central AGN is not the most common cause of weak cooling flows. We investigate the role of heat conduction by electrons and find that the theoretically predicted conductivity rates are not high enough to balance radiation losses. The differential emission measure distribution has remarkable similarities with the predictions from coronal magnetic loop models. Also the physical processes involved (radiative cooling, thermal conduction along the loops, gravity) are similar for clusters loops and coronal loops. If coronal loop models apply to clusters, we find that a few hundred loops per scale height should be present. The typical loop sizes deduced from the observed emission measure distribution are consistent with the characteristic magnetic field sizes deduced from Faraday rotation measurements.
Project leadership and contacts /
Projektleitung und Kontakte
Dr. R. Piffaretti (Project Leader)  
Prof Dr. Philippe Jetzer  
Funding source(s) /
Unterstützt durch
Universität Zürich (position pursuing an academic career), Others
Duration of Project / Projektdauer Jan 2003 to Jan 2005