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PreprintarXiv licencearXiv

Galactic HII regions in LAMOST Medium-Resolution Spectroscopic Survey of Nebulae

  • Yunning Zhao
  • Wei Zhang
  • Lin Ma
  • Shiming Wen
  • Tao Jing
  • Cheng Li
  • Zheng Zheng
  • Aiyuan Yang
  • Shichao Han
  • Juanjuan Ren
  • Jianjun Chen
  • Hong Wu
1 more authors
  • Yongheng Zhao
Open at sourcePDFDOICite

Abstract

Based on LAMOST Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N) data and WISE Galactic HII region catalog, we construct a sample of 280 Galactic HII regions and candidates in the Outer Galaxy (80∘ ≲ l ≲ 220∘). Using MRS-N optical spectra, we measure four emission lines (Hα, [NII]λ6584, [SII]λλ6717,6731) and use line-ratios to spectroscopically confirm 255 HII regions, including 90 previously "Known" HII regions and 165 newly classified ones. We measure their Te, ne and oxygen abundance, and determine distances via associated OB stars and the kinematic method. The sample spans Rgal from 8.16 to 15.36 kpc, enabling investigation of radial gradients in physical properties. We find [NII]/Hα and [SII]/Hα decrease with increasing Rgal, while [SII]/[NII] remains nearly flat; these trends are quite different from diffuse ionized gas (DIG). We derive the Te gradient of 344.530 ± 78.083 K kpc−1, and the log ne gradient of -0.143 ± 0.041 cm−3 kpc−1. Oxygen abundance shows a steep slope of -0.044 ± 0.010 dex kpc−1 in the inner disk and a shallow slope of -0.016 ± 0.005 dex kpc−1 in the outer disk, with a global slope of -0.014 ± 0.005 dex kpc−1. We also examine the two-dimensional distributions of Te, ne, and oxygen abundance, and find the gradients vary with azimuth. There is no obvious difference between spiral arm and interarm regions, and no trend appears along individual arms. From [NII]/Hα-[SII]λ6717/Hα diagram, HII regions have a S+/S ratio (0.32), lower than DIG (0.43); however, heavy overlap prevents clear separation from this diagram alone.

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Cite

BibTeXRIS
BibTeX
@misc{zhao2026galactic,
  title = {{Galactic HII regions in LAMOST Medium-Resolution Spectroscopic Survey of Nebulae}},
  author = {Yunning Zhao and Wei Zhang and Lin Ma and Shiming Wen and Tao Jing and Cheng Li and Zheng Zheng and Aiyuan Yang and Shichao Han and Juanjuan Ren and Jianjun Chen and Hong Wu and Yongheng Zhao},
  howpublished = {arXiv},
  year = {2026},
  month = jul,
  doi = {10.48550/arxiv.2607.27662},
  eprint = {2607.27662},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2607.27662},
}
RIS
TY  - UNPB
TI  - Galactic HII regions in LAMOST Medium-Resolution Spectroscopic Survey of Nebulae
AU  - Yunning Zhao
AU  - Wei Zhang
AU  - Lin Ma
AU  - Shiming Wen
AU  - Tao Jing
AU  - Cheng Li
AU  - Zheng Zheng
AU  - Aiyuan Yang
AU  - Shichao Han
AU  - Juanjuan Ren
AU  - Jianjun Chen
AU  - Hong Wu
AU  - Yongheng Zhao
PY  - 2026
DA  - 2026/07/30
PB  - arXiv
DO  - 10.48550/arxiv.2607.27662
UR  - https://arxiv.org/abs/2607.27662
AB  - Based on LAMOST Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N) data and WISE Galactic HII region catalog, we construct a sample of 280 Galactic HII regions and candidates in the Outer Galaxy (80^∘ ≲ l ≲ 220^∘). Using MRS-N optical spectra, we measure four emission lines (Hα, [NII]λ6584, [SII]λλ6717,6731) and use line-ratios to spectroscopically confirm 255 HII regions, including 90 previously "Known" HII regions and 165 newly classified ones. We measure their T_e, n_e and oxygen abundance, and determine distances via associated OB stars and the kinematic method. The sample spans R_gal from 8.16 to 15.36 kpc, enabling investigation of radial gradients in physical properties. We find [NII]/Hα and [SII]/Hα decrease with increasing R_gal, while [SII]/[NII] remains nearly flat; these trends are quite different from diffuse ionized gas (DIG). We derive the T_e gradient of 344.530 ± 78.083 K kpc^−1, and the log n_e gradient of -0.143 ± 0.041 cm^−3 kpc^−1. Oxygen abundance shows a steep slope of -0.044 ± 0.010 dex kpc^−1 in the inner disk and a shallow slope of -0.016 ± 0.005 dex kpc^−1 in the outer disk, with a global slope of -0.014 ± 0.005 dex kpc^−1. We also examine the two-dimensional distributions of T_e, n_e, and oxygen abundance, and find the gradients vary with azimuth. There is no obvious difference between spiral arm and interarm regions, and no trend appears along individual arms. From [NII]/Hα-[SII]λ6717/Hα diagram, HII regions have a S^+/S ratio (0.32), lower than DIG (0.43); however, heavy overlap prevents clear separation from this diagram alone.
ER  -