Observational Evidence for Large-scale Gas Heating in a Galaxy Protocluster at z = 2.30

[摘要] We report az= 2.30 galaxy protocluster (COSTCO-I) in the COSMOS field, where the Ly αforest as seen in the CLAMATO IGM tomography survey does not show significant absorption. This departs from the transmission–density relationship (often dubbed the fluctuating Gunn–Peterson approximation; FGPA) usually expected to hold at this epoch, which would lead one to predict strong Ly αabsorption at the overdensity. For comparison, we generate mock Ly αforest maps by applying the FGPA to constrained simulations of the COSMOS density field and create mocks that incorporate the effects of finite sight-line sampling, pixel noise, and Wiener filtering. Averaged overr= 15h ⁻¹ Mpc around the protocluster, the observed Ly αforest is consistently more transparent in the real data than in the mocks, indicating a rejection of the null hypothesis that the gas in COSTCO-I follows the FGPA ( p= 0.0026, or 2.79 σsignificance). It suggests that the large-scale gas associated with COSTCO-I is being heated above the expectations of the FGPA, which might be due to either large-scale AGN jet feedback or early gravitational shock heating. COSTCO-I is the first known large-scale region of the IGM that is observed to be transitioning from the optically thin photoionized regime at cosmic noon to eventually coalesce into an intracluster medium (ICM) byz= 0. Future observations of similar structures will shed light on the growth of the ICM and allow constraints on AGN feedback mechanisms.