LAMOST星云中分辨率光谱巡天中的银电离氢区
Galactic HII regions in LAMOST Medium-Resolution Spectroscopic Survey of Nebulae
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中文总结 AI 辅助
该研究基于LAMOST MRS-N数据构建银盘外区电离氢区样本，测量其物理参数与径向梯度，发现与弥散电离气体不同的线比趋势，明确氧丰度梯度特征。
中文摘要 AI 辅助
基于LAMOST星云中分辨率光谱巡天（MRS-N）数据和WISE银电离氢区星表，我们构建了一个包含280个银盘外区（80°≲l≲220°）的银电离氢区及候选体样本。利用MRS-N光学光谱，我们测量了四条发射线（Hα、[NII]λ6584、[SII]λλ6717,6731），并通过线比光谱证认了255个电离氢区，其中包括90个此前“已知”的电离氢区和165个新分类的电离氢区。我们测量了这些电离氢区的电子温度Te、电子密度ne和氧丰度，并通过关联的OB星及运动学方法确定了它们的距离。该样本的银心距Rgal范围为8.16至15.36千秒差距，可用于研究物理性质的径向梯度。我们发现[NII]/Hα和[SII]/Hα随Rgal增大而减小，而[SII]/[NII]基本保持不变；这些趋势与弥散电离气体（DIG）截然不同。我们推导得到电子温度梯度为344.530±78.083 K·kpc⁻¹，log ne梯度为-0.143±0.041 cm⁻³·kpc⁻¹。氧丰度在银盘内区呈现陡峭的-0.044±0.010 dex·kpc⁻¹斜率，在外区则为平缓的-0.016±0.005 dex·kpc⁻¹斜率，全局斜率为-0.014±0.005 dex·kpc⁻¹。我们还研究了Te、ne和氧丰度的二维分布，发现梯度随方位角变化，旋臂与旋臂间区域无明显差异，且沿单个旋臂无趋势。从[NII]/Hα-[SII]λ6717/Hα图来看，电离氢区的S⁺/S比值为0.32，低于弥散电离气体的0.43；但两者重叠严重，仅通过该图无法实现清晰区分。
英文摘要
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$^{\circ}$ $\lesssim$ l $\lesssim$ 220$^{\circ}$). Using MRS-N optical spectra, we measure four emission lines (H$α$, [NII]$λ$6584, [SII]$λλ$6717,6731) and use line-ratios to spectroscopically confirm 255 HII regions, including 90 previously "Known" HII regions and 165 newly classified ones. We measure their $T_{\rm e}$, $n_{\rm e}$ and oxygen abundance, and determine distances via associated OB stars and the kinematic method. The sample spans $R_{\rm gal}$ from 8.16 to 15.36 kpc, enabling investigation of radial gradients in physical properties. We find [NII]/H$α$ and [SII]/H$α$ decrease with increasing $R_{\rm gal}$, while [SII]/[NII] remains nearly flat; these trends are quite different from diffuse ionized gas (DIG). We derive the $T_{\rm e}$ gradient of 344.530 $\pm$ 78.083 K kpc$^{-1}$, and the $\log n_{\rm e}$ gradient of -0.143 $\pm$ 0.041 cm$^{-3}$ kpc$^{-1}$. Oxygen abundance shows a steep slope of -0.044 $\pm$ 0.010 dex kpc$^{-1}$ in the inner disk and a shallow slope of -0.016 $\pm$ 0.005 dex kpc$^{-1}$ in the outer disk, with a global slope of -0.014 $\pm$ 0.005 dex kpc$^{-1}$. We also examine the two-dimensional distributions of $T_{\rm e}$, $n_{\rm e}$, 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]/H$α$-[SII]$λ$6717/H$α$ 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.
