CO enhancement by magnetohydrodynamic waves: Striations in the Polaris Flare
CO enhancement by magnetohydrodynamic waves: Striations in the Polaris Flare
复制标题
磁流体动力波增强二氧化碳：北极星耀斑中的条纹
DOI：
10.1051/0004-6361/202345880
复制
发表时间：
2023
影响因子：
6.5
通讯作者：
Goldsmith, P. F.
中科院分区：
文献类型：
--
作者：
Skalidis, R.;Gkimisi, K.;Tassis, K.;Panopoulou, G. V.;Pelgrims, V.;Tritsis, A.;Goldsmith, P. F.
星际云中分子气体的形成是一个缓慢的过程，但可以通过气体压缩来增强。磁流体动力学（MHD）波可以产生压缩的准周期线性结构，称为条纹。条纹观察到的柱密度，在该过渡从原子到分子气体happened.AimsWe探索的MHD波在CO化学中的作用，在分子clouds.MethodsWe有针对性的条纹在北极星耀斑云的区域。我们进行了COJ= 2 - 1的调查，以探测分子气体的性质。我们使用档案星光偏振数据和尘埃发射图，以探测磁场特性和比较对CO的形态和运动学特性。我们评估了可压缩MHD波模式与CO化学的相互作用，通过比较它们的特征timescale.ResultsThe估计的磁场为38-76 μG。在CO积分强度图中，我们观察到一个占主导地位的准周期强度结构，往往是平行的磁场方向，并具有约1秒差距的波长。周期轴与平均磁场方向偏离约17°，也在尘埃强度图中观察到。CO积分强度图中的对比度比柱密度图的对比度高约2.4倍，表明CO形成局部增强。我们认为，一个主要的慢磁声模式，估计周期为2.1-3.4百万年，传播速度为0.30-0.45 km s-1，可能促进了CO的形成，因此创造了观察到的周期性图案。我们还建议，在不确定性，一个快速的磁声模式，周期为0.48万年和速度为2.0公里s-1可能发挥了一定的作用，在增加CO abundance.ConclusionsQuasiperiodic CO结构中观察到的条纹区域可能是印记的MHD波模式。Alfvénic速度设定了可压缩MHD模式的动力学时间尺度，并确定了CO化学中涉及的波模式。
ContextThe formation of molecular gas in interstellar clouds is a slow process, but can be enhanced by gas compression. Magneto-hydrodynamic (MHD) waves can create compressed quasi-periodic linear structures, referred to as striations. Striations are observed at the column densities at which the transition from atomic to molecular gas takes place.AimsWe explore the role of MHD waves in the CO chemistry in regions with striations within molecular clouds.MethodsWe targeted a region with striations in the Polaris Flare cloud. We conducted a COJ= 2−1 survey in order to probe the molecular gas properties. We used archival starlight polarization data and dust emission maps in order to probe the magnetic field properties and compare against the CO morphological and kinematic properties. We assessed the interaction of compressible MHD wave modes with CO chemistry by comparing their characteristic timescales.ResultsThe estimated magnetic field is 38–76 µG. In the CO integrated intensity map, we observe a dominant quasiperiodic intensity structure that tends to be parallel to the magnetic field orientation and has a wavelength of approximately one parsec. The periodicity axis is ~17° off from the mean magnetic field orientation and is also observed in the dust intensity map. The contrast in the CO integrated intensity map is ~2.4 times higher than the contrast of the column density map, indicating that CO formation is enhanced locally. We suggest that a dominant slow magnetosonic mode with an estimated period of 2.1–3.4 Myr and a propagation speed of 0.30–0.45 km s−1is likely to have enhanced the formation of CO, hence created the observed periodic pattern. We also suggest that within uncertainties, a fast magnetosonic mode with a period of 0.48 Myr and a velocity of 2.0 km s−1could have played some role in increasing the CO abundance.ConclusionsQuasiperiodic CO structures observed in striation regions may be the imprint of MHD wave modes. The Alfvénic speed sets the dynamical timescales of the compressible MHD modes and determines which wave modes are involved in the CO chemistry.