Molecular clumps towards compact H II regions

Abstract

To better understand how the H II regions can affect their surrounding molecular clouds we have studied the molecular distribution towards three compact H II regions associated with IRAS sources (08140-3559, 09014-4736, and 09026-4842) by means of the observations of ¹²CO, ¹³CO, and C¹⁸O molecules in the J = 3-2 transition with the APEX telescope. In two cases, we show evidence of possible disruption of the molecular clouds and increasing turbulence towards the diffuse H α emissions, which could be due to the ionizing front. We find 11 clumps towards the IRAS sources either nearby or surrounding the H II regions. Their parameters, such as the optical depths, column densities, masses, and [¹³CO/C¹⁸O] abundances, were calculated assuming LTE conditions. We discuss the behaviour of such parameters and we have found that the [¹³CO/C¹⁸O] abundances in the IRAS sources associated with a diffuse H α emission are higher than the abundances in regions where no H α emission is detected, indicating that such a parameter could be affected by the UV field coming from H II region. We also discuss the rise of the average [H₂/¹³CO] and [H₂/C¹⁸O] abundances in the IRAS sources which show evidence of disruption of molecular clouds by the expansion of the H II regions. With these average abundances, we estimate the LTE total mass of each clump and compare them with the virial mass to discuss whether our clumps are gravitationally stable.