## Hector Hiss

Hector Hiss  ( Brasil/Germany )

hiss @ mpia.de

Measuring the Thermal State of the Intergalactic Medium Using High Resolution Spectra of the Lyman-$\alpha$ Forest at $2 < z < 4$
In my thesis I analyze the thermal evolution of the intergalactic medium in order to gain insight on the evolution of the bulk of the baryonic matter in the universe and understand global processes of reionization and the timing and sources driving it.
The low density medium between galaxies (the intergalactic medium, IGM) serves as an excellent calorimeter. The long cooling time-scales of this gas allows it to retain memory of any phase transition that alters its thermal state. In my thesis I analyze neutral hydrogen absorption profiles that appear in the spectra of distant quasars while their light traveled through the IGM (The Lyman-$\alpha$ forest). The distribution of absorber line-width versus absorber column-density from line profile fits has a distinct cutoff. This is sensitive to the thermal state of the gas and can be used for measuring the temperature of the gas as a function of density. In addition, with the help of both hydrodynamic and collisionless simulations, I'm developing a new statistical method to extract the thermal information hidden in the distribution as a whole instead of only in this cutoff. Carrying out this kind of analysis at different redshifts allow us to track the thermal state evolution of the IGM. With this kinds of measurements we observe, in agreement with previous studies, a signature of a hot gas-phase transition at redshift of around 3 (11 billion years ago). This is attributed to heat being dumped into the IGM, as intergalactic Helium becomes doubly ionized.

Supervisor:   Joe Hennawi  ( MPIA )

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