Modelling the ArH+ emission from the Crab nebula
Modelling the ArH+ emission from the Crab nebula
复制标题
模拟蟹状星云的 ArH 发射
DOI：
10.1093/mnras/stx2327
复制
发表时间：
2017
影响因子：
4.8
通讯作者：
Priestley F
中科院分区：
文献类型：
--
作者：
Priestley F
我们进行了蟹状星云灯丝在中央脉冲星风星云的同步辐射和高通量带电粒子作用下的光电离和光解离区（PDR）联合建模；在herschelspire FTS对蟹状星云的观测中，需要一个比标准星际值（ζ0）大大增强的宇宙射线电离率来解释缺乏探测到的[Ci]发射。在SPIRE FTS频率范围内观测到的OH+和ArH+跃迁的谱线表面亮度比只能用较高的宇宙射线电离率和较低的ArH+解离重组率来解释，尽管与实验上限一致。我们发现，nh = 2 × 104cm−3,ζ = 107ζ0的模型细丝可以再现ArH+/OH+线强度和观测到的h2振动-旋转发射，并且在蟹状星云中尘埃球的范围内可见消光，尽管[Oi]和[Cii]的远红外发射高于观测约束。nh = 1900 cm−3的模型低估了h2表面亮度，但与ArH+和OH+表面亮度一致，预测的[Oi]和[Cii]线比与观测值一致。这些模型预测HeH+的旋转发射高于探测阈值，但考虑到形成时间尺度，蟹状星云中这种分子的丰度应该低于我们分析中获得的平衡值。
We have performed combined photoionization and photodissociation region (PDR) modelling of a Crab nebula filament subjected to the synchrotron radiation from the central pulsar wind nebula, and to a high flux of charged particles; a greatly enhanced cosmic-ray ionization rate over the standard interstellar value, ζ0, is required to account for the lack of detected [Ci] emission in publishedHerschelSPIRE FTS observations of the Crab nebula. The observed line surface brightness ratios of the OH+and ArH+transitions seen in the SPIRE FTS frequency range can only be explained with both a high cosmic-ray ionization rate and a reduced ArH+dissociative recombination rate compared to that used by previous authors, although consistent with experimental upper limits. We find that the ArH+/OH+line strengths and the observed H2vibration–rotation emission can be reproduced by model filaments withnH= 2 × 104cm−3, ζ = 107ζ0and visual extinctions within the range found for dusty globules in the Crab nebula, although far-infrared emission from [Oi] and [Cii] is higher than the observational constraints. Models withnH= 1900 cm−3underpredict the H2surface brightness, but agree with the ArH+and OH+surface brightnesses and predict [Oi] and [Cii] line ratios consistent with observations. These models predict HeH+rotational emission above detection thresholds, but consideration of the formation time-scale suggests that the abundance of this molecule in the Crab nebula should be lower than the equilibrium values obtained in our analysis.