Constraining the temperature–density relation of the intergalactic medium with the Lyman α and β forests

Elisa Boera, Michael T. Murphy, George D. Becker, James S. Bolton
2015 Monthly Notices of the Royal Astronomical Society: Letters  
The post-reionization thermal state of the intergalactic medium is characterized by a power-law relationship between temperature and density, with a slope determined by the parameter $\gamma$. We describe a new method to measure $\gamma$ using the ratio of flux curvature in the Lyman-$\alpha$ and $\beta$ forests. At a given redshift, this curvature ratio incorporates information from the different gas densities traced by Lyman-$\alpha$ and $\beta$ absorption. It is relatively simple and fast to
more » ... simple and fast to compute and appears robust against several observational uncertainties. We apply this technique to a sample of 27 high-resolution quasar spectra from the Very Large Telescope. While promising statistical errors on $\gamma$ appear to be achievable with these spectra, to reach its full potential, the dependence of the curvature ratio on the thermal state of the gas in the foreground Lyman-$\alpha$ forest will require further, detailed forward modelling.
doi:10.1093/mnrasl/slv172 fatcat:5p67fejenrch7pimlv3tfwhl4i