Speaker
Mr
Alberto Rorai
(Max Planck Institute for Astronomy - Heidelberg)
Description
The small scale structure of the IGM, quantified by the Jeans filtering scale, has fundamental cosmological implications. On the one hand, it provides a thermal record of the heat injected by UV photons during cosmic reionization events, and its value thus constrains the thermal and reionization history of the Universe. On the other hand, it sets the minimum mass scale for gravitational collapse from the IGM, and hence plays a pivotal role in galaxy formation. Unfortunately, it is extremely challenging to measure from the standard technique of analyzing purely longitudinal Lyα forest spectra, because thermal broadening is highly degenerate with the Jeans filtering. However, it can be directly measured by characterizing the coherence of Lyα forest absorption in close quasar pair spectra whose small separations ~ 100 kpc resolve the Jeans scale. We have developed a novel technique to directly measure the Jeans filtering based on analyzing the probability distribution of phase angle differences of homologous Fourier modes in close quasar pair spectra. A Bayesian formalism is introduced based on this new method, which combined with MCMC simulations, allows us to characterize the precision of a hypothetical Jeans scale measurement and explore degeneracies with other parameters governing the temperature density relation of the IGM (T0,gamma). A large grid (500) of thermal models is generated by combining a large dark matter simulation with a semi-analytical model of the Lyα forest. Our full parameter study indicates that a realistic sample of 20 close quasar pair spectra can measure the Jeans scale to 5% precision, fully independent of the temperature-density relation of the IGM. We will provide a progress report on our very recent effort to use this new technique to make the first measurement of the Jeans scale with real quasar pair spectra.
