The contribution of X-ray binaries to the evolution of late-type galaxies: Evolutionary population synthesis simulations

X-ray studies of normal late-type galaxies have shown that non-nuclear X-ray emission is typically dominated by X-ray binaries, and provides a useful measure of star formation activity. We have modeled the X-ray evolution of late-type galaxies over the $\sim$ 14 Gyr of cosmic history, with an evolutionary population synthesis code developed by Hurley et al. Our calculations reveal a decrease of the X-ray luminosity-to-mass ratio $L_{\rm X}/M$ with time, in agreement with observations (Fig.~7$a$). We show that this decrease is a natural consequence of stellar and binary evolution and mass accumulating process in galaxies. The X-ray-to-optical luminosity ratio $L_{\rm X}/L_{\rm B}$ is found to be fairly constant (around $\sim 10^{30}$ erg\,s$^{-1}$$L_{\rm B,\odot}^{-1}$, Fig.~7$b$), and insensitive to the star formation history in the galaxies. The nearly constant value of $L_{\rm X}/L_{\rm B}$ is in conflict with the observed increase in $L_{\rm X}/L_{\rm B}$ from $z=0$ to 1.4. The discrepancy may be caused by intense obscured star formation activity that leads to nonlinear relationship between X-ray and B-band emission.Comment: 8 figures, 1 table, accepted for publication in the Astrophysical Journal, now available at http://stacks.iop.org/0004-637X/733/

Optimal Discrete Uniform Generation from Coin Flips, and Applications

This article introduces an algorithm to draw random discrete uniform variables within a given range of size n from a source of random bits. The algorithm aims to be simple to implement and optimal both with regards to the amount of random bits consumed, and from a computational perspective---allowing for faster and more efficient Monte-Carlo simulations in computational physics and biology. I also provide a detailed analysis of the number of bits that are spent per variate, and offer some extensions and applications, in particular to the optimal random generation of permutations.Comment: first draft, 22 pages, 5 figures, C code implementation of algorith

The nature of the unresolved extragalactic soft CXB

In this paper we investigate the power spectrum of the unresolved 0.5-2 keV CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal which, on scales >30", is significantly higher than the Shot-Noise and is increasing with the angular scale. We interpreted this signal as the joint contribution of clustered undetected sources like AGN, Galaxies and Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall, our modeling predicts that \sim 20% of the unresolved CXB flux is made by low luminosity AGN, \sim 25% by galaxies and \sim 55% by the IGM (Inter Galactic Medium). We do not find any direct evidence of the so called Warm Hot Intergalactic Medium (i.e. matter with 10^5K<T<10^7K and density contrast {\delta} <1000), but we estimated that it could produce about 1/7 of the unresolved CXB. We placed an upper limit to the space density of postulated X-ray-emitting early black hole at z>7.5 and compared it with SMBH evolution models.Comment: 15 pages, 9 figures, accepted by MNRA

Can AGN and galaxy clusters explain the surface brightness fluctuations of the cosmic X-ray background?

Fluctuations of the surface brightness of cosmic X-ray background (CXB) carry unique information about faint and low luminosity source populations, which is inaccessible for conventional large-scale structure (LSS) studies based on resolved sources. We used Chandra data of the XBOOTES field ($\sim9\,\mathrm{deg^2}$) to conduct the most accurate measurement to date of the power spectrum of fluctuations of the unresolved CXB on the angular scales of $\sim3\,$arcsec $-$ $\sim17\,$arcmin. We find that at sub-arcmin angular scales, the power spectrum is consistent with the AGN shot noise, without much need for any significant contribution from their one-halo term. This is consistent with the theoretical expectation that low-luminosity AGN reside alone in their dark matter halos. However, at larger angular scales we detect a significant LSS signal above the AGN shot noise. Its power spectrum, obtained after subtracting the AGN shot noise, follows a power law with the slope of $-0.8\pm0.1$ and its amplitude is much larger than what can be plausibly explained by the two-halo term of AGN. We demonstrate that the detected LSS signal is produced by unresolved clusters and groups of galaxies. For the flux limit of the XBOOTES survey, their flux-weighted mean redshift equals \left\sim0.3, and the mean temperature of their intracluster medium (ICM), \left\approx 1.4 keV, corresponds to the mass of $M_{500} \sim 10^{13.5}\,\mathrm{M}_\odot$. The power spectrum of CXB fluctuations carries information about the redshift distribution of these objects and the spatial structure of their ICM on the linear scales of up to $\sim$Mpc, i.e. of the order of the virial radius.Comment: 25 pages, 20 figures, submitted to MNRAS, comments welcom

From Quantum Systems to L-Functions: Pair Correlation Statistics and Beyond

The discovery of connections between the distribution of energy levels of heavy nuclei and spacings between prime numbers has been one of the most surprising and fruitful observations in the twentieth century. The connection between the two areas was first observed through Montgomery's work on the pair correlation of zeros of the Riemann zeta function. As its generalizations and consequences have motivated much of the following work, and to this day remains one of the most important outstanding conjectures in the field, it occupies a central role in our discussion below. We describe some of the many techniques and results from the past sixty years, especially the important roles played by numerical and experimental investigations, that led to the discovery of the connections and progress towards understanding the behaviors. In our survey of these two areas, we describe the common mathematics that explains the remarkable universality. We conclude with some thoughts on what might lie ahead in the pair correlation of zeros of the zeta function, and other similar quantities.Comment: Version 1.1, 50 pages, 6 figures. To appear in "Open Problems in Mathematics", Editors John Nash and Michael Th. Rassias. arXiv admin note: text overlap with arXiv:0909.491

Noise versus chaos in a causal Fisher-Shannon plane

We revisit the Fisher-Shannon representation plane ${\mathcal H} \times {\mathcal F}$, evaluated using the Bandt and Pompe recipe to assign a probability distribution to a time series. Several stochastic dynamical (noises with $f^{-k}$, $k \geq 0$, power spectrum) and chaotic processes (27 chaotic maps) are analyzed so as to illustrate the approach. Our main achievement is uncovering the informational properties of the planar location.Comment: 6 pages, 1 figure. arXiv admin note: text overlap with arXiv:1401.213