Work

Dense cores in the vicinity of an H II region

Year: 2026

Type: article

Abstract: Context . Massive stars form in the densest part of molecular clouds and strongly influence their surroundings through radiative and mechanical feedback. The effects of such feedback on dense gas structures at sub-parsec scales, however, remain to be better constrained by observations. Aims . We aim to investigate how feedback from a newly formed massive star affects the physical properties of dense cores embedded in a neighboring filamentary molecular cloud. Methods . We analyzed the ALMA Band 6 observations of the filamentary source IRAS 18530+0215 (I18530), including 1.3 mm dust continuum, molecular line emission from DCN, N 2 D + , and 13 CS, as well as complementary VLA K-band continuum and NH 3 metastable line observations. The dynamical state of the ultracompact (UC) H II region was investigated through energy and pressure estimates. Dense cores traced by the line emission were identified using the astrodendro algorithm, and their temperatures, masses, velocity dispersions, and virial parameters were derived from molecular line fitting and continuum emission. We further examined how the physical and kinematic properties of the dense cores vary under the influence of feedback from the H II region. Results . The H II region has a radius of ∼0.1 pc and exhibits an expansion velocity of ∼2.5 km s −1 , corresponding to a shell dynamical age of ∼0.06 Myr. The DCN and 13 CS cores are primarily distributed in the vicinity of the H II region, whereas N 2 D + cores are preferentially found at larger distances. Overall, the temperatures and velocity dispersions of the dense cores show clear decreasing trends with increasing projected distance from the H II region. The virial parameters increase with projected distance within the inner ∼0.3 pc but decline sharply beyond this scale, while the core masses show no significant variation with distance. Strong star formation signatures are found at projected distances of ∼0.2 pc from the H II region, whereas more distant regions still host quiescent, cold dense cores at earlier evolutionary stages. Conclusions . Our results suggest that the compact H II region is currently trapped or choked within a scale of ∼0.1 pc. Its feedback extends to at least ∼0.3 pc and is unlikely to significantly disrupt the entire filamentary structure on short timescales. Within the affected region, the feedback enhances the velocity dispersions, gas temperatures, and virial parameters of the dense cores, with no evidence that it promotes the formation of more massive dense cores.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661676