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Register a new userEffervescent heating: constraints from nearby cooling flow clusters observed with XMM-Newton
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We have used deprojected radial density and temperature profiles of a sample of 16 nearby CF clusters observed with XMM-Newton to test whether the effervescent heating model can satisfactorily explain the dynamics of CF clusters. For each cluster we derived the required extra heating as a function of cluster-centric distance for various values of the unknown parameters $dot M$ (mass deposition rate) and $f_c$ (conduction efficiency). We fitted the extra heating curve using the AGN effervescent heating function and derived the AGN parameters $L$ (the time-averaged luminosity) and $r_0$ (the scale radius where the bubbles start rising in the ICM). While we do not find any solution with the effervescent heating model for only one object, we do show that AGN and conduction heating are not cooperating effectively for half of the objects in our sample. For most of the clusters we find that, when a comparison is possible, the derived AGN scale radius $r_0$ and the observed AGN jet extension have the same order of magnitude. The AGN luminosities required to balance radiative losses are substantially lowered if the fact that the AGN deposits energy within a finite volume is taken into account. For the Virgo cluster, we find that the AGN power derived from the effervescent heating model is in good agreement with the observed jet power.
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We investigate temperature and entropy profiles of 13 nearby cooling flow clusters observed with the EPIC cameras of XMM-Newton. When normalized and scaled by the virial radius the temperature profiles turn out to be remarkably similar. At large radii the temperature profiles show a clear decline starting from a break radius at ~ 0.1 r_vir. The temperature decreases by ~30 % between 0.1 r_vir and 0.5 r_vir. As expected for systems where non-gravitational processes are of great importance, the scale length characterizing the central temperature drop is not found to be proportional to the virial radius of the system. The entropy of the plasma increases monotonically moving outwards almost proportional to the radius and the central entropy level is tightly correlated with the core radius of the X-ray emission. The dispersion in the entropy profiles is smaller if the empirical relation S propto T^{0.65} is used instead of the standard self-similar relation S propto T and, as expected for cooling flow clusters, no entropy cores are observed.
We present results from the XMM-Newton observations of our ongoing program on merging clusters. To date three clusters have been observed, covering the temporal sequence from early to late stage mergers: A1750, A2065 and A3921. Using spatially-resolved spectroscopy of discrete regions, hardness ratio and temperature maps, we show that all three clusters display a complex temperature structure. In the case of A1750, a double cluster, we argue that the observed temperature structure is not only related to the ongoing merger but also to previous merger events. A2065 seems an excellent example of a `compact merger, i.e. when the centres of the two clusters have just started to interact, producing a shock in the ICM. Using comparisons with numerical simulations and complementary optical data, the highly complex temperature structure evident in A3921 is interpreted as an off-axis merger between two unequal mass components. These results illustrate the complex physics of merger events. The relaxation time can be larger than the typical time between merger events, so that the present day morphology of clusters depends not only on on-going interaction but also on the more ancient formation history.
Clusters of galaxies contain a hot gas, which emits in X-rays. X-ray telescopes such as XMM-Newton allow to study this plasma to obtain information on physical quantities of these objects. We present here some results on the total mass density distribution of clusters obtained with XMM-Newton based on the hydrostatic approach. These results can be compared to models based on cold dark matter. Generally good agreement is found between observations and models. Furthermore we present a study on physical properties of a distant merging cluster of galaxies, which demonstrates the potential of XMM-Newton studies on this class of objects.
We have analyzed XMM-Newton Optical Monitor (OM) UV (180-400 nm) data for a sample of 33 galaxies, of which 30 are cluster members. Nine of these are central cluster galaxies (CCGs) in cooling flow clusters, having mass deposition rates which span a range of 8 to 525 solar masses per year. Using the ratio of UV to 2MASS J band flux, we find a significant UV excess in many, but not all, cooling flow CCGs. This UV excess is a direct indication of the presence of young massive stars, and therefore recent star formation, in these galaxies. Using the Starburst99 spectral energy distribution (SED) model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2 to 219 solar masses per year for the cooling flow sample. For 2/3 of this sample it is possible to equate Chandra/XMM cooling flow mass deposition rates with UV inferred star formation rates, for a combination of starburst lifetime and IMF slope. This is a pilot study of the well populated XMM UV cluster archive and a more extensive follow up study is currently underway.
We examine high signal to noise XMM-Newton European Photon Imaging Camera (EPIC) and Reflection Grating Spectrometer (RGS) observations to determine the physical characteristics of the gas in the cool core and outskirts of the nearby rich cluster A3112. The XMM-Newton Extended Source Analysis Software data reduction and background modeling methods were used to analyze the XMM- Newton EPIC data. From the EPIC data we find that the iron and silicon abundance gradients show significant increase towards the center of the cluster while the oxygen abundance profile is centrally peaked but has a shallower distribution than that of iron. The X-ray mass modeling is based on the temperature and deprojected density distributions of the intra-cluster medium determined from EPIC observations. The total mass of A3112 obeys the M-T scaling relations found using XMM-Newton and Chandra observations of massive clusters at R500. The gas mass fraction f_gas= 0.149^{+0.036}_{-0.032} at R500, is consistent with the seven-year WMAP results. The comparisons of line fluxes and flux limits on the Fe XVII and Fe XVIII lines obtained from high resolution RGS spectra indicate that there is no spectral evidence for cooler gas associated with the cluster with temperature below 1.0 keV in the central <38 (sim 52 kpc) region of A3112. High resolution RGS spectra also yield an upper limit to the turbulent motions in compact core of A3112 (206 km/s). We find that the energy contribution of turbulence to total energy is less than 6 per cent. This upper limit is consistent with the amount of energy contribution measured in recent high resolution simulations of relaxed galaxy clusters.
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