The Intrinsic Multiphase Gas--Black Hole Connection across Scales in IllustrisTNG

The relationship between supermassive black holes and the multiphase circumgalactic medium is central to understanding the co-evolution of galaxies and their central black holes. We investigate this relationship using the IllustrisTNG100 simulation with a sample of 5089 central galaxies at z=0, measuring the partial correlation between central black hole mass and the mass of cold (T < 10 4 K), cool (10 4 T < 10 5 K), warm (10 5 T < 10 6 K), and hot (T 10 6 K) gas within 0.03R 200, 0.15R 200, and R 200, after accounting for stellar and dark matter halo mass. We find that after removing these confounding factors, black hole mass shows a significant negative partial correlation (rho about-0.37) with cold gas within R 200 and 0.15R 200, whereas warm and hot gas exhibit no substantial intrinsic correlation. The residual plane reveals a threshold pattern: galaxies with over-massive black holes show systematically reduced cold gas, consistent with the cumulative impact of AGN feedback. The anti-correlation persists across environments with a weak trend in local density, and varies with galaxy type (star-forming, green valley, and quenched). These results provide a quantitative multiphase diagnostic of AGN feedback in TNG and support a picture in which feedback progressively removes cold gas, offering testable predictions for future multiwavelength surveys.