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OATS-DAUT SEMINAR
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Speaker: Alberto Rorai (MPIA, Heidelberg, Germany)
Title: Measuring the Jeans scale of the IGM with close quasar pair
Date: Wednesday, November 20th, 2013
Time: 11:30
Venue: Villa Bazzoni
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Abstract 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 Ly-alpha
forest spectra, because thermal broadening is highly degenerate with
the Jeans filtering. However, it can be directly measured by
characterizing the coherence of Ly-alpha 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 Ly-a 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. I 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.
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Contact: Stefano Cristiani (OATS)