The ionization fraction in OMC-2 and OMC-3
The ionization fraction in OMC-2 and OMC-3
复制标题
OMC-2 和 OMC-3 中的电离分数
DOI：
10.1051/0004-6361/202140670
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发表时间：
2021
影响因子：
6.5
通讯作者：
Tielens, A. G.
中科院分区：
文献类型：
--
作者：
Salas, P.;Rugel, M. R.;Emig, K. L.;Kauffmann, J.;Menten, K. M.;Wyrowski, F.;Tielens, A. G.
电子密度（ne−）在设定星际介质的化学和物理方面起着重要作用。然而，在这方面，中性云中Ne-的直接测量或间接测量一直以来都是在少数几条观测线上进行的，目的是利用碳射电复合谱线和C+的远红外谱线直接测量猎户座A分子云中的Ne-和整体形丝包层中的气体温度。方法观测了猎户座A分子云中的C102α（6109.901 MHz）和C109α（5011.420 MHz）碳射电复合谱线（CRRL）。由于CRRL具有相似的谱线特性，我们将其平均以增加光谱的信噪比。我们比较了平均CRRL的强度，和158 μm-[CII]和[13 CII]线的预测的一个均匀的模型的C+/C界面的信封的分子云，并从这个比较，我们确定的电子密度，温度和C+柱密度的气体。其中，它们的速度（vLSR <$11 km s−1）和宽度（σv <$1 km s−1）证实了它们跟踪ISF的包络。在两个位置上，我们探测到CRRL，以及信噪比≥5的158 μm-[CII]和[13 CII]谱线，我们发现ne −= 0.65 ± 0.12 cm− 3和0.95 ± 0.02 cm−3，这对应于气体密度H =<$5 × 103 cm − 3和热压力p =<$4 × 105 K cm−3。用HCN（1-0）和C2 H（1-0）谱线tox（e−）≤ 3 × 1 - 0 − 6来限制分子云较密区域的电离分数。结论电子密度和电离分数表明，在C+层和HCN（1-0）探测区域之间x（e−）下降了≥100倍。这表明电子碰撞激发在设定HCN（1-0）的激发朝向所研究的区域中不起重要作用，因为它仅对所观察到的发射的约10%负责。
ContextThe electron density (ne−) plays an important role in setting the chemistry and physics of the interstellar medium. However, measurements ofne−in neutral clouds have been directly obtained only toward a few lines of sight or they rely on indirect determinations.AimsWe use carbon radio recombination lines and the far-infrared lines of C+to directly measurene−and the gas temperature in the envelope of the integral shaped filament (ISF) in the Orion A molecular cloud.MethodsWe observed the C102α(6109.901 MHz) and C109α(5011.420 MHz) carbon radio recombination lines (CRRLs) using the Effelsberg 100 m telescope at ≈2′ resolution toward five positions in OMC-2 and OMC-3. Since the CRRLs have similar line properties, we averaged them to increase the signal-to-noise ratio of the spectra. We compared the intensities of the averaged CRRLs, and the 158 μm-[CII] and [13CII] lines to the predictions of a homogeneous model for the C+/C interface in the envelope of a molecular cloud and from this comparison we determined the electron density, temperature and C+column density of the gas.ResultsWe detect the CRRLs toward four positions, where their velocity (vLSR≈ 11 km s−1) and widths (σv≈ 1 km s−1) confirms that they trace the envelope of the ISF. Toward two positions we detect the CRRLs, and the 158 μm-[CII] and [13CII] lines with a signal-to-noise ratio ≥5, and we findne−= 0.65 ± 0.12 cm−3and 0.95 ± 0.02 cm−3, which corresponds to a gas densitynH≈ 5 × 103cm−3and a thermal pressure ofpth≈ 4 × 105K cm−3. We also constrained the ionization fraction in the denser portions of the molecular cloud using the HCN(1–0) and C2H(1–0) lines tox(e−) ≤ 3 × 10−6.ConclusionsThe derived electron densities and ionization fraction imply thatx(e−) drops by a factor ≥100 between the C+layer and the regions probed by HCN(1–0). This suggests that electron collisional excitation does not play a significant role in setting the excitation of HCN(1–0) toward the region studied, as it is responsible for only ≈10% of the observed emission.