Turbulent molecular gas and star formation in the shocked intergalactic medium of Stephan's Quintet
Pierre Guillard, François Boulanger, Guillaume Pineau des Forêts, Edith Falgarone, Antoine Gusdorf, Michelle Cluver, Philip Appleton, Ute Lisenfeld, Pierre-Alai… 展开作者
Pierre Guillard, François Boulanger, Guillaume Pineau des Forêts, Edith Falgarone, Antoine Gusdorf, Michelle Cluver, Philip Appleton, Ute Lisenfeld, Pierre-Alain Duc, Patrick Ogle, Kevin Xu
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Revised abstract and small editing to match published version. 15 pages, 5 figures. Accepted for publication in ApJ
We report on single-dish radio CO observations towards the inter-galactic medium (IGM) of the Stephan's Quintet (SQ) group of galaxies. Extremely bright mid-IR H2 rotational line emission from warm molecular gas has been detected by Spitzer in the kpc-scale shock created by a galaxy collision. We detect in the IGM CO(1-0), (2-1) and (3-2) line emission with complex profiles, spanning a velocity range of 1000 km/s. The spectra exhibit the pre-shock recession velocities of the two colliding gas systems (5700 and 6700 km/s), but also intermediate velocities. This shows that much of the molecular gas has formed out of diffuse gas accelerated by the galaxy-tidal arm collision. A total H2 mass of 5x10^9 Msun is detected in the shock. The molecular gas carries a large fraction of the gas kinetic energy involved in the collision, meaning that this energy has not been thermalized yet. The turbulent kinetic energy of the H2 gas is at least a factor of 5 greater than the thermal energy of the hot plasma heated by the collision. The ratio between the warm H2 mass derived from Spitzer IRS spectroscopy and the H2 mass derived from CO fluxes is ~0.3 in the IGM of SQ, which is 10-100 times higher than in star-forming galaxies. In the shocked region, the ratio of the PAH-to-CO surface luminosities, commonly used to measure the star formation efficiency of the H2 gas, is lower (up to a factor 75) than the observed values in star-forming galaxies. We suggest that turbulence fed by the galaxy-tidal arm collision maintains a high heating rate within the H2 gas. This interpretation implies that the velocity dispersion on the scale of giant molecular clouds in SQ is one order of magnitude larger than the Galactic value. The high amplitude of turbulence may explain why this gas is not forming stars efficiently. [abridged version]
Shock-Enhanced C+ Emission and the Detection of H2O from Stephan's Quintet's Group-Wide Shock using Herschel
我们首次用赫歇尔光谱探测到了[OI]63和[CII]158微米的精细结构跃迁，以及斯蒂芬五重奏中35 x 15 kpc^2的受激星系际暗条中的一条para-H2O谱线。这条暗条被认为是当一个高速入侵者与星团内气体碰撞时形成的。PACS光谱仪的观测提供了宽（> 1000 km s^-1）的发光[CII]谱线轮廓以及较暗的[OI] 63微米发射的证据。SPIRE FTS观测揭示了细丝中几个位置的p-H2O（111-000）跃迁的水发射，但没有其他分子线。H2O谱线很窄，可能与密度较大的中速气体经历最强的冲击加热有关。[CII]/PAH（tot）和[CII]/FIR比率太大，无法通过PDR中的正常光电加热来解释。也可以排除HII区激发或X射线/宇宙射线加热。观测结果得出的结论是，大部分分子气体是扩散和温暖的。我们建议，[CII]，[OI]和暖H2线的发射是由一个湍流级联，其中的动能从星系碰撞与IGM耗散到小尺度和低速度，通过冲击和湍流涡旋。低速磁震可以帮助解释[CII]/[OI]比值和观察到的相对较高的[CII]/H2比值。发现[CII]发射可以增强，在大规模的湍流区域的碰撞环境中的影响的解释[CII]发射在高z星系。
New insights on Stephan's Quintet: exploring the shock in three dimensions
我们进行了IFU光谱的三个点和附近的SQ冲击。我们使用PMAS的3.5米卡拉尔阿尔托望远镜获得的发射线，提供洞察气体的物理性质的措施。Hα和[NII]6548、6583 A发射线在许多spaxels中的严重混合需要至少两个运动学分量的假设，以便提取各条线的通量。我们研究的主要结果包括：（a）在新的入侵者速度范围5400- 6000公里/秒内探测到离散发射特征，显示出与HII区一致的特性，（b）探测到速度在5800- 6300公里/秒范围内的低速成分，其性质类似于太阳金属丰度冲击气体;与低金属量冲击气体的性质一致。这两个冲击分量被解释为NGC 7318 b新侵入者与其路径上的碎片场碰撞的产物，这产生了一种复杂的电离气体结构，其中有几种具有不同运动学和物理特性的成分共存，尽管与NGC 7318 b有关的原始ISM的一部分仍然存在，并且保持不变。我们的观测结果表明，低速电离分量可能在新的入侵者碰撞之前就已经存在，并且可能与Williams等人（2002）的NW-LV HI分量有关。高速电离分量可能填补了SQ-A和NGC 7319潮丝中观测到的HI复合体之间的空隙（NW-HV，Arc-N和Arc-S in Williams et al. 2002）。
