Pressure components in the central HII regions

There are observational constraints on the magnitudes and time-scales of early stellar feedback in low ISM pressure environments, yet no such constraints exist for more cosmologically typical high ISM pressure environments.

In this paper, we determine the mechanisms dominating the expansion of HII regions as a function of size-scale and evolutionary time within the high-pressure (P/k_B_~10^7-8^K.cm^-3^) environment in the inner 100pc of the Milky Way. We calculate the thermal pressure from the warm ionized (P_HII_; 10^4^K) gas, direct radiation pressure (P_dir_), and dust processed radiation pressure (P_IR_). We find that (1) P_dir_ dominates the expansion on small scales and at early times (0.01-0.1pc; <0.1Myr); (2) the expansion is driven by P_HII_ on large scales at later evolutionary stages (>0.1pc; >1Myr); (3) during the first ~<1Myr of growth, but not thereafter, either P_IR_ or stellar wind pressure likely make a comparable contribution.