M~33（{ \tt HerM33es }）光谱分辨CII发射：BCLMP 691周围的物理条件和运动学
Spectrally resolved CII emission in M~33 ({\tt HerM33es}): Physical conditions and kinematics around BCLMP 691
摘要：
这项工作提供了在158 \CII处\CII的高光谱分辨率观测，\CII是星际介质的主要冷却线之一，使用Herschel卫星上的HIFI外差光谱仪进行观测。在BCLMP 691中，M33星盘的极北（3.3 kpc）的\HII \区域，\CII \和CO线剖面在$0.5 \kms$中显示出相似的速度，而\HI \线速度被$\sim 5\kms$系统地移向较低的旋转速度。在相同的$12"$角分辨率下观察到，\CII比CO宽约50%，但比\HI窄。\CII与远红外连续光谱的比值表明光电加热效率为1.1%。这些数据与已发表的模型一起表示以太阳邻域值为单位的UV场$G_0 \sim 100$、气体密度$n_H \sim 1000 \cc$和气体温度$T\sim 200$ K。采用这些值，我们估计C $^+$色谱柱密度为$N_{C^+} \approx 1.3 \times 10^{17} \cmt$。\CII \发射主要来自\HII \区域和其后面的冷分子云之间的温暖中性区域。根据已发表的丰度，推断的C $^+$柱对应于氢柱密度$N_H \sim 2 \times 10^{21} \cmt$。CO观察结果表明，$N_H = 2 N_{H_2} \sim 3.2 \times 10^{21} \cmt$和21 cm测量值（同样在$12"$分辨率下）产生的$N_\HI \approx 1.2 \times 10^{21} \cmt$在\CII \速度范围内。因此，一些H $_2$没有检测到在CO中必须存在，在协议的基础上的SPIRE 250 - 500 $μ$ m发射的早期研究结果。
英文摘要：
This work presents high spectral resolution observations of the \CII\ line at 158 \micron, one of the major cooling lines of the interstellar medium, taken with the HIFI heterodyne spectrometer on the Herschel satellite. In BCLMP 691, an \HII\ region far north (3.3 kpc) in the disk of M 33, the \CII\ and CO line profiles show similar velocities within $0.5 \kms$, while the \HI\ line velocities are systematically shifted towards lower rotation velocities by $\sim 5\kms$. Observed at the same $12"$ angular resolution, the \CII\ lines are broader than those of CO by about 50% but narrower than the \HI\ lines. The \CII\ line to far-infrared continuum ratio suggests a photoelectric heating efficiency of 1.1%. The data, together with published models indicate a UV field $G_0 \sim 100$ in units of the solar neighborhood value, a gas density $n_H \sim 1000 \cc$, and a gas temperature $T\sim 200$ K. Adopting these values, we estimate the C$^+$ column density to be $N_{C^+} \approx 1.3 \times 10^{17} \cmt$. The \CII\ emission comes predominantly from the warm neutral region between the \HII\ region and the cool molecular cloud behind it. From published abundances, the inferred C$^+$ column corresponds to a hydrogen column density of $N_H \sim 2 \times 10^{21} \cmt$. The CO observations suggest that $N_H = 2 N_{H_2} \sim 3.2 \times 10^{21} \cmt$ and 21cm measurements, also at $12"$ resolution, yield $N_\HI \approx 1.2 \times 10^{21} \cmt$ within the \CII\ velocity range. Thus, some H$_2$ not detected in CO must be present, in agreement with earlier findings based on the SPIRE 250 -- 500 $μ$m emission.
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