Tuesday

An open problem in cosmology is the determination of the precise thermal history of the Universe, more specifically, the redshift of reionization, and the subsequent evolution of the UV background, which sets the temperature of the intergalactic medium.
One way which we can try to measure it is through the Lyman-alpha forest. This gives us a 'longitudinal' view of the intergalactic medium at high redshifts.
The broadening of absorption lines is the sum of two components: thermal broadening, characterised by the 'equation of state' of the IGM, and 'Hubble broadening', an effect arising from the Hubble flow in the filaments of the cosmic web. Most previous studies of the Lyman-alpha forest have focused on the former, modelling the equation of state as a power-law, and using quasar spectra to constrain the two parameters of the power-law. It has been argued in the literature (e.g. arXiv:1502.05715) that one should include a third parameter to model the Hubble broadening, which measures the scale of baryonic matter density fluctuations. This parameter would depend not just on the current thermal state of the IGM, but on its whole thermal history.
In this talk, I will present our analysis of mock spectra generated from a range of state-of-the-art cosmological simulations taken from the EAGLE suite (Schaye+2015, Crain+2015) and discuss whether we have a viable technique for measuring the thermal history.