The Origin of the Spatial Distribution of X-ray luminous AGN in Massive Galaxy Clusters

We study the spatial distribution of a 95% complete sample of 508 X-ray point sources (XPS) detected in the 0.5-2.0 keV band in Chandra ACIS-I observations of 51 massive galaxy clusters found in the MACS survey. Covering the redshift range z=0.3-0.7, our cluster sample is statistically complete and comprises all MACS clusters with X-ray luminosities in excess of 4.5 x 10^44 erg/s (0.1-2.4 keV, h_0=0.7, LCDM). Also studied are 20 control fields that do not contain clusters. We find the XPS surface density, computed in the cluster restframe, to exhibit a pronounced excess within 3.5 Mpc of the cluster centers. The excess, believed to be caused by AGN in the cluster, is significant at the 8.0 sigma confidence level compared to the XPS density observed at the field edges. No significant central excess is found in the control fields. To investigate the physical origin of the AGN excess, we study the radial AGN density profile for a subset of 24 virialized clusters. We find a pronounced central spike (r<0.5 Mpc), followed by a depletion region at about 1.5 Mpc, and a broad secondary excess centered at approximately the virial radius of the host clusters (~2.5 Mpc). We present evidence that the central AGN excess reflects increased nuclear activity triggered by close encounters between infalling galaxies and the giant cD-type elliptical occupying the very cluster center. By contrast, the secondary excess at the cluster-field interface is likely due to black holes being fueled by galaxy mergers. In-depth spectroscopic and photometric follow-up observations of the optical counterparts of the XPS in a subset of our sample are being conducted to confirm this picture.Comment: ApJ Letters, accepted (4 pages, 3 figures, uses emulateapj

Entropy and Long range correlations in literary English

Recently long range correlations were detected in nucleotide sequences and in human writings by several authors. We undertake here a systematic investigation of two books, Moby Dick by H. Melville and Grimm's tales, with respect to the existence of long range correlations. The analysis is based on the calculation of entropy like quantities as the mutual information for pairs of letters and the entropy, the mean uncertainty, per letter. We further estimate the number of different subwords of a given length $n$. Filtering out the contributions due to the effects of the finite length of the texts, we find correlations ranging to a few hundred letters. Scaling laws for the mutual information (decay with a power law), for the entropy per letter (decay with the inverse square root of $n$) and for the word numbers (stretched exponential growth with $n$ and with a power law of the text length) were found.Comment: 8 page

Statistical keyword detection in literary corpora

Understanding the complexity of human language requires an appropriate analysis of the statistical distribution of words in texts. We consider the information retrieval problem of detecting and ranking the relevant words of a text by means of statistical information referring to the "spatial" use of the words. Shannon's entropy of information is used as a tool for automatic keyword extraction. By using The Origin of Species by Charles Darwin as a representative text sample, we show the performance of our detector and compare it with another proposals in the literature. The random shuffled text receives special attention as a tool for calibrating the ranking indices.Comment: Published version. 11 pages, 7 figures. SVJour for LaTeX2

Thermodynamics of hot dense H-plasmas: Path integral Monte Carlo simulations and analytical approximations

This work is devoted to the thermodynamics of high-temperature dense hydrogen plasmas in the pressure region between $10^{-1}$ and $10^2$ Mbar. In particular we present for this region results of extensive calculations based on a recently developed path integral Monte Carlo scheme (direct PIMC). This method allows for a correct treatment of the thermodynamic properties of hot dense Coulomb systems. Calculations were performed in a broad region of the nonideality parameter $\Gamma \lesssim 3$ and degeneracy parameter $n_e \Lambda^3 \lesssim 10$. We give a comparison with a few available results from other path integral calculations (restricted PIMC) and with analytical calculations based on Pade approximations for strongly ionized plasmas. Good agreement between the results obtained from the three independent methods is found.Comment: RevTex file, 21 pages, 5 ps-figures include

The evolution of the cluster X-ray scaling relations in the WARPS sample at 0.6<z<1.0

The X-ray properties of a sample of 11 high-redshift (0.6<z<1.0) clusters observed with Chandra and/or XMM are used to investigate the evolution of the cluster scaling relations. The observed evolution of the L-T and M-L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the universe at their redshift of observation. When the systematic effect of assuming isothermality on the derived masses of the high-redshift clusters is taken into account, the high-redshift M-T and Mgas-T relations are also consistent with self-similar evolution. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L-T relation is consistent with the high-z clusters having formed at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L-T relation at high-redshift (B=3.29+/-0.38) is consistent with the local relation, and significantly steeper then the self-similar prediction of B=2. This suggests that the non-gravitational processes causing the steepening occurred at z>1 or in the early stages of the clusters' formation, prior to their observation. The properties of the intra-cluster medium at high-redshift are found to be similar to those in the local universe. The mean surface-brightness profile slope for the sample is 0.66+/-0.05, the mean gas mass fractions within R2500 and R200 are 0.073+/-0.010 and 0.12+/-0.02 respectively, and the mean metallicity of the sample is 0.28+/-0.16 solar.Comment: 23 pages, 17 figures. Accepted for publication in MNRAS. Revised to match accepted version: reanalysed data with latest calibrations, several minor changes. Conclusions unchange