Measuring the temperature of the high-redshift intergalactic medium

Understanding the thermal evolution of the high-z intergalactic medium (IGM) is of fundamental importance in cosmology. The temperature and density of the IGM are related by an equation of state of the form $T(\Delta) = T_0 (\Delta)^{\gamma - 1}$ where $\Delta$ is the overdensity. Several previous attempts to constrain the parameters ($T_0$ and $\gamma$) of this equation of state involved the fitting of absorption lines in the spectra of quasars, which leads to somewhat large uncertainties. Recent work has pointed to the existence of characteristic values for the overdensities in the high-redshift universe, at which a flux statistic, known as the mean curvature, exhibits a tight correlation with the gas temperature. Using the mean curvature leads to much smaller uncertainties but does not constrain both the parameters of the equation of state. I will describe how the  curvature is found to be sensitive to the additional heating effects in the near-zones of high-redshift quasars, which indicate the beginning stages of helium reionization in the universe. I will also describe how the median and percentiles of the curvature are associated with temperatures measured at different characteristic overdensities, and how these can be used together to efficiently constrain both the parameters of the equation of state. The characteristic overdensities are found to have a direct physical interpretation and describe absorbers having sizes of the order of the Jeans' scale in the IGM. This novel approach could help us to accurately constrain the thermal evolution of the high-redshift universe. Understanding the thermal evolution of the high-z intergalactic medium (IGM) is of fundamental importance in cosmology. The temperature and density of the IGM are related by an equation of state of the form $T(\Delta) = T_0 (\Delta)^{\gamma - 1}$ where $\Delta$ is the overdensity. Several previous attempts to constrain the parameters ($T_0$ and $\gamma$) of this equation of state involved the fitting of absorption lines in the spectra of quasars, which leads to somewhat large uncertainties. Recent work has pointed to the existence of characteristic values for the overdensities in the high-redshift universe, at which a flux statistic, known as the mean curvature, exhibits a tight correlation with the gas temperature. Using the mean curvature leads to much smaller uncertainties but does not constrain both the parameters of the equation of state. I will describe how the  curvature is found to be sensitive to the additional heating effects in the near-zones of high-redshift quasars, which indicate the beginning stages of helium reionization in the universe. I will also describe how the median and percentiles of the curvature are associated with temperatures measured at different characteristic overdensities, and how these can be used together to efficiently constrain both the parameters of the equation of state. The characteristic overdensities are found to have a direct physical interpretation and describe absorbers having sizes of the order of the Jeans' scale in the IGM. This novel approach could help us to accurately constrain the thermal evolution of the high-redshift universe.