论文标题
扩展弥散云中ARH+化学的视图
Extending the view of ArH+ chemistry in diffuse clouds
论文作者
论文摘要
Herschel任务的惊喜之一是在排放和吸收强大的银河背景来源中发现Arh+对螃蟹星云的检测。尽管这些检测仅限于银河系的第一个象限，但现有数据表明ARH+普遍存在，仅探测ISM的弥漫性原子区域。在这项研究中，我们将ARH+的覆盖范围扩展到银河系的其他部分，其J = 1-0沿七个银河视线线向明亮的亚MM连续源进行了新的观察结果。我们的目标是通过评估其与其他众所周知的原子和分子气体示踪剂的相关性（或缺乏）来基准其作为纯原子气体的示踪剂的效率。 ARH+接近617.5 GHz的观察结果可与新的，敏感的SEPIA660接收器在Apex 12 M望远镜上进行可行。该接收器的两个边带使我们能够与ARH+线同时观察到607.227 GHz的P-H2O+过渡。通过分析OH+和O-H2O+的稳态化学，我们平均得出2.3e-16 s^-1的宇宙射线电离速率（CRIR），降低了这项工作中研究的视线。使用CRIR的派生值和观察到的ARH+丰度，我们限制了通过ARH+追踪的气体的分子分数位于2E-2以下，中位数为8.8E-4。合并，我们对ARH+，OH+，H2O+和CH探针的观察结果，从弥漫性原子到弥漫性和半透明的分子云。在银河系尺度上，我们看到N（ARH+）的分布与N（H）的分布相关，尤其是在内部星系中，在较大的Galactacentric距离下，原子气的温暖中性中性中性相位有可能贡献。我们得出H2O+为2.1的平均O/P比率，该核自旋温度与41 K的核自旋温度相对应，与弥漫性云的典型气体温度一致。
One of the surprises of the Herschel mission was the detection of ArH+ towards the Crab Nebula in emission and in absorption towards strong Galactic background sources. Although these detections were limited to the first quadrant of the Galaxy, the existing data suggest that ArH+ ubiquitously and exclusively probes the diffuse atomic regions of the ISM. In this study, we extend the coverage of ArH+ to other parts of the Galaxy with new observations of its J = 1-0 transition along seven Galactic sight lines towards bright sub-mm continuum sources. We aim to benchmark its efficiency as a tracer of purely atomic gas by evaluating its correlation (or lack there of) with other well-known atomic and molecular gas tracers. The observations of ArH+ near 617.5 GHz were made feasible with the new, sensitive SEPIA660 receiver on the APEX 12 m telescope. The two sidebands of this receiver allowed us to observe p-H2O+ transitions of at 607.227 GHz simultaneously with the ArH+ line. By analysing the steady state chemistry of OH+ and o-H2O+, we derive on average a cosmic-ray ionisation rate (CRIR), of 2.3e-16 s^-1 towards the sight lines studied in this work. Using the derived values of the CRIR and the observed ArH+ abundances we constrain the molecular fraction of the gas traced by ArH+ to lie below 2e-2 with a median value of 8.8e-4. Combined, our observations of ArH+, OH+, H2O+, and CH probe different regimes of the ISM, from diffuse atomic to diffuse and translucent molecular clouds. Over Galactic scales, we see that the distribution of N(ArH+) is associated with that of N(H), particularly in the inner Galaxy with potentially even contributions from the warm neutral medium phase of atomic gas at larger galactocentric distances. We derive an average o/p-ratio for H2O+ of 2.1, which corresponds to a nuclear spin temperature of 41 K, consistent with the typical gas temperatures of diffuse clouds.
