Temperature of the neutral CGM around high-redshift galaxies

Gas in galaxy halos is the result of an interplay between the AGN/stellar outflows and the inflows from intergalactic medium. Observational constraints on the CGM properties provide a clue for the cosmological simulations and shed a light on the feedback mechanisms, which are responsible for the baryonic cycle and determine the CGM energy distribution. Due to the complex nature of CGM, understanding of the feedback processes requires a comprehensive study of the halo gas in hot ionized as well as warm and cold neutral phases. Unfortunately, in contrast with a cold and ionized gas, estimation of the temperature of warm phase is a difficult task. This can be overcome using the analysis of the absorption lines imprinted onto quasar spectra (Noterdaeme et al. 2021).  We present such measurements of the warm CGM temperature, based on a sample of Damped Lyman-alpha systems in high-resolution high-redshift (z~2) VLT/UVES spectra. We show that warm neutral circum-galactic gas demonstrates a huge variety of estimated temperatures, which in some cases exceed the canonical Galactic value of ~10 000 K generally assumed in thermal balance models.

Noterdaeme et al., A&A 651, A78 (2021)