Molecular gas associated with HII regions

We derived spectral line parameters via multicomponent Gaussian fitting, which was then used to constrain the physical conditions determined using PyRADEX, a non-local thermodynamic equilibrium (LTE) radiative transfer code in combination with Markov chain Monte Carlo analysis. The non-LTE analysis yielded kinetic temperatures (Tkin) ranging from 33.7K to 265K and H_2_ densities (n(H_2_)) between 0.8x10^4^ and 1.05x10^7^cm^-3^, providing a detailed characterization of the dense -olecular gas contained in these clumps.

In addition to the p-H_2_CO emission arising from the targeted clump, a large fraction (57%) of the sources exhibited multiple p-H_2_CO components, with the secondary components being characterized by a higher Tkin and broader line widths. Investigation of the nature of the secondary component revealed its association with supersonic nonthermal motions and turbulent gas. When comparing the physical properties of the molecular gas and dust components with those of the ionized gas, we found that parameters directly linked to the central high-mass star, such as bolometric luminosity (Lbol) and Lyman continuum photon rate (NLyc), show stronger and more systematic correlations.

These findings emphasize the role of the central star in governing the interplay between the molecular and ionized gas. In our sample of HII regions, the pressure of the neutral gas systematically exceeds that of the ionized gas. This suggests that the surrounding neutral molecular medium can hinder or slow down the expansion of HII regions due to its higher pressure.

However, given the limited spatial resolution, a definitive conclusion on the role of molecular gas in confining HII regions cannot be made until high resolution observations are obtained.