The Fate of Intracluster Radio Plasma

Radio plasma injected by active radio galaxies into clusters of galaxies quickly becomes invisible due to radiative losses of the relativistic electrons. In this talk, the fate of radio plasma and its role for the galaxy cluster is discussed: buoyancy removes it from the central regions and allows to transfer its energy into the ambient gas. The remaining low energy electron populations are still able to emit a low luminosity glow of observable radiation via synchrotron-self Comptonized emission. Shock waves in the ambient gas can re-ignite the radio emission.Comment: Invited Talk at `Matter and Energy in Clusters of Galaxies', Taipei 2002, 8 pages, 6 figures, uses newpasp.sty (includued

Reconstruction of signals with unknown spectra in information field theory with parameter uncertainty

The optimal reconstruction of cosmic metric perturbations and other signals requires knowledge of their power spectra and other parameters. If these are not known a priori, they have to be measured simultaneously from the same data used for the signal reconstruction. We formulate the general problem of signal inference in the presence of unknown parameters within the framework of information field theory. We develop a generic parameter uncertainty renormalized estimation (PURE) technique and address the problem of reconstructing Gaussian signals with unknown power-spectrum with five different approaches: (i) separate maximum-a-posteriori power spectrum measurement and subsequent reconstruction, (ii) maximum-a-posteriori power reconstruction with marginalized power-spectrum, (iii) maximizing the joint posterior of signal and spectrum, (iv) guessing the spectrum from the variance in the Wiener filter map, and (v) renormalization flow analysis of the field theoretical problem providing the PURE filter. In all cases, the reconstruction can be described or approximated as Wiener filter operations with assumed signal spectra derived from the data according to the same recipe, but with differing coefficients. All of these filters, except the renormalized one, exhibit a perception threshold in case of a Jeffreys prior for the unknown spectrum. Data modes, with variance below this threshold do not affect the signal reconstruction at all. Filter (iv) seems to be similar to the so called Karhune-Loeve and Feldman-Kaiser-Peacock estimators for galaxy power spectra used in cosmology, which therefore should also exhibit a marginal perception threshold if correctly implemented. We present statistical performance tests and show that the PURE filter is superior to the others.Comment: 21 pages, 5 figures, accepted by PR

The Radio Luminosity Function of Cluster Radio Halos

A significant fraction of galaxy clusters exhibits cluster wide radio halos. We give a simple prediction of the local and higher redshift radio halo luminosity function (RHLF) on the basis of (i) an observed and a theoretical X-ray cluster luminosity function (XCLF) (ii) the observed radio--X-ray luminosity correlation (RXLC) of galaxy clusters with radio halos (iii) an assumed fraction of 1/3 galaxy clusters to have radio halos as supported by observations. We then find 300-700 radio halos with S_1.4GHz > 1 mJy, and 10^5 - 10^6 radio halos with S_1.4GHz > 1 muJy should be visible on the sky. 14% of the S_1.4GHz > 1 mJy and 56% of the S_1.4GHz > 1 muJy halos are located at z>0.3. Subsequently, we give more realistic predictions taking into account (iv) a refined estimate of the radio halo fraction as a function of redshift and cluster mass, and (v) a decrease in intrinsic radio halo luminosity with redshift due to increased inverse Compton electron energy losses on the Cosmic Microwave Background (CMB). We find that this reduces the radio halo counts from the simple prediction by only 30 % totally, but the high redshift (z>0.3) counts are more strongly reduced by 50-70%. These calculations show that the new generation of sensitive radio telescopes like LOFAR, ATA, EVLA, SKA and the already operating GMRT should be able to detect large numbers of radio halos and will provide unique information for studies of galaxy cluster merger rates and associated non-thermal processes.Comment: Accepted by A&A, 8 pages, 7 figure