Sergio Colafrancesco — Page 3

arXiv1999

High- and low energy nonthermal X-ray emission from the cluster of galaxies A 2199

We report the detection of both soft and hard excess X-ray emission in the cluster of galaxies A 2199, based upon spatially resolved spectroscopy with data from the BeppoSAX, EUVE and ROSAT missions. The excess emission is visible at radii larger than 300 kpc and increases in strength relative to the isothermal component. The total 0.1-100 keV luminosity of this component is 15 % of the cluster luminosity, but it dominates the cluster luminosity at high and low energies. We argue that the most plausible interpretation of the excess emission is an inverse Compton interaction between the cosmic microwave background and relativistic electrons in the cluster. The observed spatial distribution of the non-thermal component implies that there is a large halo of cosmic ray electrons between 0.5-1.5 Mpc surrounding the cluster core. The prominent existence of this component has cosmological implications, as it is significantly changing our picture of a clusters's particle acceleration history, dynamics between the thermal and relativistic media, and total mass budgets.

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arXiv1999

Evolution with redshift of the ICM abundances

We predict the behaviour of the abundances of $α$-elements and iron in the intracluster medium as a function of redshift in poor and rich clusters. In order to do that we calculate the detailed chemical evolution of elliptical galaxies by means of one-zone and multi-zone models and then we integrate the contributions to the total gas and single elements by ellipticals over the cluster mass function at any given cosmic time which is then transformed into redshift according to the considered cosmological model. We refer to the one-zone model for ellipticals as to burst model and to the multi-zone model as to continuous model. We find that in the case of the burst model the ICM abundances should be quite constant starting from high redshifts ($z > 2$) up to now, whereas in the continuous model the ICM abundances should increase up to $z \sim 1$ and are almost constant from $z \sim 1$ up to $z=0$. Particular attention is devoted to the predictions of the $[α/Fe]_{ICM}$ ratio in the ICM: for the burst model we predict $[α/Fe]_{ICM}>0$ over the whole range of redshifts and in particular at $z =0$, whereas in the case of the continuous model we predict a decreasing $[α/Fe]_{ICM}$ ratio with decreasing $z$ and $[α/Fe]_{ICM} \le 0$ at $z= 0$. In particular, we predict $[O/Fe]_{ICM}(z=0) \le +0.35$ dex and $[Si/Fe]_{ICM}(z=0) \le +0.15$ dex for the bursts models and $[O/Fe]_{ICM}(z=0) \le -0.05$ dex and $[Si/Fe]_{ICM}(z=0) \le +0.13$ dex for the continuous models, the precise values depending on the assumed cosmology. Finally, we discuss the influence of different cosmologies on the results.

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