The gradient of diffuse gamma-ray emission in the Galaxy

We show that the well-known discrepancy between the radial dependence of the Galactic cosmic ray (CR) nucleon distribution, as inferred most recently from EGRET observations of diffuse gamma-rays above 100 MeV, and of the most likely CR source distribution (supernova remnants, pulsars) can be explained purely by PROPAGATION effects. Contrary to previous claims, we demonstrate that this is possible, if the dynamical coupling between the escaping CRs and thermal plasma is taken into account, and thus a self-consistent GALACTIC WIND calculation is carried out. Given a dependence of the CR source distribution on Galactocentric radius, r, our numerical wind solutions show that the CR outflow velocity, V(r,z) depends both on r, and on vertical distance, z, at reference level z_C. The latter is defined as the transition boundary from diffusion to advection dominated CR transport and is therefore also a function of r. In fact, the CR escape time averaged over particle energies decreases with increasing CR source strength. Such an increase is counteracted by a reduced average CR residence time in the gas disk. Therfore pronounced peaks in the radial source distribution result in mild radial gamma-ray gradients at GeV energies, as it has been observed. This effect is enhanced by anisotropic diffusion, assuming different radial and vertical diffusion coefficients. We have calculated 2D analytic solutions of the stationary diffusion-advection equation, including anisotropic diffusion, for a given CR source distribution and a realistic outflow velocity field V(r,z), inferred from self-consistent numerical Galactic Wind simulations. At TeV energies the gamma-rays from the sources are expected to dominate the observed "diffuse" flux from the disk. Its observation should allow an empirical test of the theory presented.Comment: 23 pages, 12 figures; accepted for publication in Astronomy and Astrophysics Main Journa

Dynamic Order-Sorted Term-Rewriting Systems

This thesis considers the problems of order-sorted equational logic and its operational interpretation, order-sorted term rewriting

Foreground component separation with generalised ILC

The 'Internal Linear Combination' (ILC) component separation method has been extensively used to extract a single component, the CMB, from the WMAP multifrequency data. We generalise the ILC approach for separating other millimetre astrophysical emissions. We construct in particular a multidimensional ILC filter, which can be used, for instance, to estimate the diffuse emission of a complex component originating from multiple correlated emissions, such as the total emission of the Galactic interstellar medium. The performance of such generalised ILC methods, implemented on a needlet frame, is tested on simulations of Planck mission observations, for which we successfully reconstruct a low noise estimate of emission from astrophysical foregrounds with vanishing CMB and SZ contamination.Comment: 11 pages, 6 figures (2 figures added), 1 reference added, introduction expanded, V2: version accepted by MNRA

Testing Isotropy of Cosmic Microwave Background Radiation

We introduce new symmetry-based methods to test for isotropy in cosmic microwave background radiation. Each angular multipole is factored into unique products of power eigenvectors, related multipoles and singular values that provide 2 new rotationally invariant measures mode by mode. The power entropy and directional entropy are new tests of randomness that are independent of the usual CMB power. Simulated galactic plane contamination is readily identified, and the new procedures mesh perfectly with linear transformations employed for windowed-sky analysis. The ILC -WMAP data maps show 7 axes well aligned with one another and the direction Virgo. Parameter free statistics find 12 independent cases of extraordinary axial alignment, low power entropy, or both having 5% probability or lower in an isotropic distribution. Isotropy of the ILC maps is ruled out to confidence levels of better than 99.9%, whether or not coincidences with other puzzles coming from the Virgo axis are included. Our work shows that anisotropy is not confined to the low l region, but extends over a much larger l range.Comment: 40 pages 15 figure

Analytical Solutions to the Mass-Anisotropy Degeneracy with Higher Order Jeans Analysis: A General Method

The Jeans analysis is often used to infer the total density of a system by relating the velocity moments of an observable tracer population to the underlying gravitational potential. This technique has recently been applied in the search for Dark Matter in objects such as dwarf spheroidal galaxies where the presence of Dark Matter is inferred via stellar velocities. A precise account of the density is needed to constrain the expected gamma ray flux from DM self-annihilation and to distinguish between cold and warm dark matter models. Unfortunately the traditional method of fitting the second order Jeans equation to the tracer dispersion suffers from an unbreakable degeneracy of solutions due to the unknown velocity anisotropy of the projected system. To tackle this degeneracy one can appeal to higher moments of the Jeans equation. By introducing an analog to the Binney anisotropy parameter at fourth order, beta' we create a framework that encompasses all solutions to the fourth order Jeans equations rather than those in the literature that impose unnecessary correlations between anisotropy of second and fourth order moments. The condition beta' = f(beta) ensures that the degeneracy is lifted and we interpret the separable augmented density system as the order-independent case beta'= beta. For a generic choice of beta' we present the line of sight projection of the fourth moment and how it could be incorporated into a joint likelihood analysis of the dispersion and kurtosis. Having presented the mathematical framework, we then use it to develop a statistical method for the purpose of placing constraints on dark matter density parameters from discrete velocity data. The method is tested on simulated dwarf spheroidal data sets leading to results which motivate study of real dwarf spheroidal data sets.Comment: 21 pages, 15 figures. Accepted by MNRAS. Typo corrected in eq. 3

Comparing Stellar Populations of Galaxies across the Hubble Sequence: Reduction of PISCES Near-Infrared Images

To better understand the properties of high redshift galaxies and improve models of galaxy formation, we are investigating color radial profiles to study the stellar age, dust and metallicity distribution of galaxies of varying lumi-nosities and morphological types. Current data obtained in the optical and UV have shown that early-type galaxies have a flat color profile, or are bluer at larger radii, while late-type spirals are redder with increasing radius. These trends are believed to be linked with stellar population ages or dust. To break the age-dust degeneracy as well as to avoid the metallicity dependence, we have obtained near-infrared images of Nearby Field Galaxy Survey (NFGS) galax-ies taken with the PISCES Wide-field Infrared Camera on the 90-inch Bok Telescope. Combined with the optical and UV data, these new, near-infrared images will help better constrain these parameters and determine the ages of the stellar components of the galaxies. We discuss the method used to process and reduce the data and present the radial profile of the surface brightness and color of one particular galaxy in the sample, UGC 439