A wavelet analysis of QSO spectra

TL;DR

This paper introduces a wavelet-based method to analyze QSO spectra, enabling detailed characterization of IGM temperature fluctuations and their relation to absorption line-widths in the Lyman-alpha forest.

Contribution

The paper presents a novel wavelet decomposition technique for QSO spectra that correlates wavelet amplitudes with IGM temperature and density, allowing spatially localized temperature analysis.

Findings

Wavelet amplitudes correlate with IGM temperature and density.

Method can identify temperature fluctuations along the spectrum.

Wavelets provide a unique, localized spectral decomposition.

Abstract

The temperature of the intergalactic medium (IGM) is an important factor in determining the line-widths of the absorption lines in the Lyman-alpha forest. We present a method to characterise the line-widths distribution using a decomposition of a Lyman-alpha spectrum in terms of discrete wavelets. Such wavelets form an orthogonal basis so the decomposition is unique. We demonstrate using hydrodynamic simulations that the mean and dispersion of the wavelet amplitudes is strongly correlated with both the temperature of the absorbing gas and its dependence on the gas density. Since wavelets are also localised in space, we are able to analyse the temperature distribution as a function of position along the spectrum. We illustrate how this method could be used to identify fluctuations in the IGM temperature which might result from late reionization or local effects.