Dense Cores in the Vicinity of an HII Region

Abstract

Massive stars strongly influence their surroundings through radiative and mechanical feedback, but its effects on dense gas structures at sub-pc scales remain poorly constrained. We investigate how feedback from a newly formed massive star affects dense cores in the filamentary molecular cloud IRAS 18530+0215. We analyze ALMA Band 6 observations of 1.3 mm dust continuum and DCN, N₂D⁺, and ¹³CS line emission, together with VLA K-band continuum and NH₃ observations. Dense cores are identified with astrodendro, and their temperatures, masses, velocity dispersions, and virial parameters are derived. The dynamical state of the ultra-compact H II region is examined through energy and pressure estimates. The H II region has a radius of ∼0.1 pc and an expansion velocity of ∼2.5 km s⁻¹, corresponding to a shell dynamical age of ∼0.06 Myr. DCN and ¹³CS cores are concentrated near the H II region, whereas N₂D⁺ cores preferentially lie farther away. Core temperatures and velocity dispersions decrease with projected distance from the H II region. Virial parameters increase within the inner ∼0.3 pc but decline sharply beyond this scale, while core masses show no significant trend with distance. Strong star formation signatures are found at ∼0.2 pc, whereas more distant regions still host quiescent, cold dense cores. The compact H II region appears trapped or choked within ∼0.1 pc, while its feedback extends to at least ∼0.3 pc. Within this region, feedback enhances core velocity dispersions, gas temperatures, and virial parameters, with no evidence that it promotes the formation of more massive dense cores.

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BibTeX RIS

BibTeX

@misc{zhang2026dense,
  title = {{Dense Cores in the Vicinity of an HII Region}},
  author = {Ruofei Zhang and Xing Lu and Jingwen Wu and Sihan Jiao and Hauyu Baobab Liu and Guang-Xing Li and Roberto Galván-Madrid and Aiyuan Yang and Siju Zhang and Shanghuo Li and Fengwei Xu and Xindi Tang and Yu Cheng and Weiyuan Zhang and Andrés E. Guzmán and Yuxin Lin and Yuhua Liu and Qizhou Zhang and Patricio Sanhueza and Ke Wang and Siyi Feng and Linjing Feng and Fangyuan Deng and Hao Ruan and Yuanzhen Xiong and Yuxiang Liu},
  howpublished = {arXiv},
  year = {2026},
  month = aug,
  doi = {10.48550/arxiv.2608.27913},
  eprint = {2608.27913},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2608.27913},
}

RIS

TY  - UNPB
TI  - Dense Cores in the Vicinity of an HII Region
AU  - Ruofei Zhang
AU  - Xing Lu
AU  - Jingwen Wu
AU  - Sihan Jiao
AU  - Hauyu Baobab Liu
AU  - Guang-Xing Li
AU  - Roberto Galván-Madrid
AU  - Aiyuan Yang
AU  - Siju Zhang
AU  - Shanghuo Li
AU  - Fengwei Xu
AU  - Xindi Tang
AU  - Yu Cheng
AU  - Weiyuan Zhang
AU  - Andrés E. Guzmán
AU  - Yuxin Lin
AU  - Yuhua Liu
AU  - Qizhou Zhang
AU  - Patricio Sanhueza
AU  - Ke Wang
AU  - Siyi Feng
AU  - Linjing Feng
AU  - Fangyuan Deng
AU  - Hao Ruan
AU  - Yuanzhen Xiong
AU  - Yuxiang Liu
PY  - 2026
DA  - 2026/08/28
PB  - arXiv
DO  - 10.48550/arxiv.2608.27913
UR  - https://arxiv.org/abs/2608.27913
AB  - Massive stars strongly influence their surroundings through radiative and mechanical feedback, but its effects on dense gas structures at sub-pc scales remain poorly constrained. We investigate how feedback from a newly formed massive star affects dense cores in the filamentary molecular cloud IRAS 18530+0215. We analyze ALMA Band 6 observations of 1.3 mm dust continuum and DCN, N_2D^+, and ^13CS line emission, together with VLA K-band continuum and NH_3 observations. Dense cores are identified with astrodendro, and their temperatures, masses, velocity dispersions, and virial parameters are derived. The dynamical state of the ultra-compact H II region is examined through energy and pressure estimates. The H II region has a radius of ∼0.1 pc and an expansion velocity of ∼2.5 km s^−1, corresponding to a shell dynamical age of ∼0.06 Myr. DCN and ^13CS cores are concentrated near the H II region, whereas N_2D^+ cores preferentially lie farther away. Core temperatures and velocity dispersions decrease with projected distance from the H II region. Virial parameters increase within the inner ∼0.3 pc but decline sharply beyond this scale, while core masses show no significant trend with distance. Strong star formation signatures are found at ∼0.2 pc, whereas more distant regions still host quiescent, cold dense cores. The compact H II region appears trapped or choked within ∼0.1 pc, while its feedback extends to at least ∼0.3 pc. Within this region, feedback enhances core velocity dispersions, gas temperatures, and virial parameters, with no evidence that it promotes the formation of more massive dense cores.
ER  -

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