The Growth of Correlations in the Matter Power Spectrum

We find statistically significant correlations in the cosmological matter power spectrum over the full range of observable scales. While the correlations between individual modes are weak, the band-averaged power spectrum shows strong non-trivial correlations. The correlations are significant when the modes in either one or both bands are in the non-linear regime, and approach 100% for pairs of bands in which all the modes are non-linear. The correlations are weaker, but not absent, when computed in redshift space. Since estimates of the power spectrum from galaxy surveys require band-averaging, the correlations must be taken into account when comparing a measured power spectrum with theoretical models.Comment: 7 pages, 6 Figures, accepted for publication to MNRAS. Revise

Intergalactic heating by Lyα photons including hyperfine structure corrections

Lyman-alpha photons from the first radiating sources in the Universe play a pivotal role in 21-cm radio detections of Cosmic Dawn and the Epoch of Reionization. Comments are provided on the effect of the hyperfine structure of hydrogen on the rate of heating or cooling of the Intergalactic Medium. It is shown that heating of the still neutral hydrogen by the Cosmic Microwave Background is negligible, with a characteristic heating time of 1e27 s/ (1+z) at redshift z.Comment: Accepted for publication in Research Notes of the AAS. (Missing reference added.

Baryonic Signatures in Large-Scale Structure

We investigate the consequences of a non-negligible baryon fraction for models of structure formation in Cold Dark Matter dominated cosmologies, emphasizing in particular the existence of oscillations in the present-day matter power spectrum. These oscillations are the remnants of acoustic oscillations in the photon-baryon fluid before last scattering. For acceptable values of the cosmological and baryon densities, the oscillations modulate the power by up to 10%, with a `period' in spatial wavenumber which is close to Delta k approximately 0.05/ Mpc. We study the effects of nonlinear evolution on these features, and show that they are erased for k > 0.2 h/ Mpc. At larger scales, the features evolve as expected from second-order perturbation theory: the visibility of the oscillations is affected only weakly by nonlinear evolution. No realistic CDM parameter combination is able to account for the claimed feature near k = 0.1 h/ Mpc in the APM power spectrum, or the excess power at 100 Mpc/h wavelengths quoted by several recent surveys. Thus baryonic oscillations are not predicted to dominate existing measurements of clustering. We examine several effects which may mask the features which are predicted, and conclude that future galaxy surveys may be able to detect the oscillatory features in the power spectrum provided baryons comprise more than 15% of the total density, but that it will be a technically challenging achievement.Comment: 16 pages, 13 Figures, to be published in MNRA

Spectral Analysis of the Lyman-Alpha Forest Using Wavelets

It is shown how wavelets may be used to analyse the absorption properties of the Lya forest. The Discrete Wavelet Transform of a QSO spectrum is used to decompose the light fluctuations that comprise the forest into orthogonal wavelets. It is demonstrated that most of the signal is carried by the moderate to lower frequency wavelets in high resolution spectra, and that a statistically acceptable description of even high signal-to-noise spectra is provided by only a fraction (10-30%) of the wavelets. The distributions of the wavelet coefficients provide a statistical basis for discriminating between different models of the Lya forest. The method is illustrated using the measured spectrum of Q1937-1009. The procedure described is readily automated and may be used to process both measured spectra and the large number of spectra generated by numerical simulations, permitting a fair comparison between the two.Comment: 8 pages, 11 figures (Figure 1b not embedded

Particle-Mesh Simulations of the Lyman-Alpha Forest

Numerical hydrodynamical simulations have proven a successful means of reproducing many of the statistical properties of the Lyman-Alpha forest as measured in high redshift quasar spectra. Pseudo-hydrodynamical methods based only on simulating the dark matter component have been claimed to yield a comparable level of success. We investigate the degree to which two pseudo-methods, with and without allowing for a pseudo-gas pressure, are able to match the predictions of fully hydrodynamical plus dark matter simulations. We also address the requirements for convergence to the statistics of the spectra and the inferred properties of the Lyman-Alpha forest as a function of resolution and box size. Generally we find it is possible to reach agreement with full hydrodynamic simulations at the 10% level in the cumulative distributions of the flux and absorption line parameter statistics for readily achievable particle and grid numbers, but difficult to do much better.Comment: 8 pages, 12 PostScript figures. Submitted to MNRA

Constraints on the UV metagalactic emissivity using the LyA forest

Numerical hydrodynamical simulations have proven a successful means of reproducing many of the statistical properties of the LyA forest as measured in high redshift (z > 4) quasar spectra. The source of ionization of the Intergalactic Medium (IGM), however, remains unknown. We investigate how the LyA forest may be used to probe the nature of the sources. We show that the attenuation of Lyman continuum photons by the IGM depends sensitively on the emissivity of the sources, permitting a strong constraint to be set on the required emissivity to match the measured values of the mean IGM LyA optical depth. We also investigate the effect of fluctuations in the UV background. We derive the distribution function of the background radiation field produced by discrete sources in an infinite universe, including the effects of attenuation by an intervening absorbing medium. We show that for z > 5, the fluctuations boost the mean LyA optical depth in a scenario in which QSO sources dominate the UV background. The fluctuations will also result in large spatial correlations in the ionization level of the IGM at high redshifts, providing a means of discriminating between scenarios in which stars and galaxies dominate the UV background vs a QSO-dominated background.Comment: 11 pages, 8 figures. Accepted for publication in MNRA