Title: ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIV. Properties of resolved UC Hii regions Show Chinese title

Title: 原子：ALMA三毫米波段观测大质量恒星形成区— XIV. 分辨率下的超 compact Hii 区的性质

Abstract: Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$\alpha$, He40$\alpha$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$\alpha$ emission. The basic parameters for these UC H{\sc ii} regions such as electron density, emission measure, electron temperature, ionic abundance ratio (n$_{\rm He^+}$/n$_{\rm H^+}$), and line width are derived. The median electron density and the median n$_{\rm He^+}$/n$_{\rm H^+}$ ratio of these UC H{\sc ii} regions derived from RRLs are $\sim$9000 cm$^{-3}$ and 0.11, respectively. Within UC H{\sc ii} regions, the n$_{\rm He^+}$/n$_{\rm H^+}$ ratios derived from the intensity ratio of the He40$\alpha$ and H40$\alpha$ lines seems to be higher in the boundary region than in the center. The H40$\alpha$ line width is mainly broadened by thermal motion and microturbulence. The electron temperature of these UC H{\sc ii} regions has a median value of $\sim$6700 K, and its dependence on galactocentric distance is weak. Show Chinese abstract

Abstract: Hydrogen recombination lines (RRLs) are one of the major diagnostics of the physical properties of H{\sc ii} regions. We use RRL H40$\alpha$, He40$\alpha$ and 3 mm continuum emission to investigate the properties of a large sample of resolved UC H{\sc ii} regions identified in the ATOMS survey. In total, we identify 94 UC H{\sc ii} regions from H40$\alpha$ emission. 这些UC H{\sc ii}区域的基本参数，例如电子密度、发射度、电子温度、离子丰度比（n$_{\rm He^+}$/n$_{\rm H^+}$）以及线宽都已推导得出。 这些由无线电再结合线推导出的 UC H{\sc ii}区域的中位电子密度和中位 n$_{\rm He^+}$/n$_{\rm H^+}$比值分别为 $\sim$9000 cm$^{-3}$和 0.11。 在UC H{\sc ii}区域内，从He40$\alpha$和H40$\alpha$线强度比得出的n$_{\rm He^+}$/n$_{\rm H^+}$比值在边界区域似乎高于中心区域。 H40$\alpha$线宽主要由热运动和微湍流展宽。 这些UC H{\sc 二}区域的电子温度中值为$\sim$6700 K，且其与星系中心距离的相关性较弱。