Speaker
Description
Overdense cosmic structures at high redshift (z~2-4) offer a unique laboratory to study the baryon cycle during the peak of galaxy assembly. This work connects the environmental impact of massive structures with the microscopic physical state of the circumgalactic medium (CGM) through a two-fold approach. First, we investigate the MQN01 protocluster, an exceptionally dense region hosting a giant, extended Lya nebula. Utilizing deep Chandra X-ray data, we examine the origin of this extended emission, revealing one of the densest and most luminous populations of AGNs ever observed at these redshifts, which acts as a primary ionizing source. Furthermore, around the brightest central AGN in the main core, we detect extended X-ray emission. A detailed investigation confirms its thermal origin, marking a direct detection of a nascent proto-Intracluster Medium (proto-ICM) and providing a rare glimpse into how the ICM forms. This system also offers a prime environment to study the co-spatial interplay between the hot and cold gas phases. Crucially, the survival and high clumpiness of the cold gas phase are strictly tied to the high pressure exerted by the surrounding hot, thermal phase. To systematically constrain this density structure and clumping factor, we then expand our analysis to a large sample of 39 quasar halos spanning z~2.1-4.5. By leveraging a powerful combination of Keck/KCWI, Keck/MOSFIRE, and VLT/MUSE data, we overcome the resonant limitations of Lya through the detection of non-resonant HeII and Ha extended emissions. Comparing the observed HeII/Ha and Lya/Ha line ratios with CLOUDY photoionization models assuming log-normal gas density distributions, we find that the high-redshift CGM is highly clumpy (clumping factors Cint > 100) and multi-phase, where dense cold gas (nH ~ 10^-1 cm^-3) is pressure-confined by the hot phase and illuminated by an ionizing spectrum. Together, these studies bridge the gap between large-scale environmental feedback from AGN and the small-scale multiphase physics of the cosmic web.