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arXiv 1410.8367astro-ph.GA
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3C 285和闵可夫斯基天体中喷流诱导的恒星形成

Jet-induced star formation in 3C 285 and Minkowski Object

Q. Salomé, P. Salomé, F. Combes

摘要:

星系中恒星形成的效率如何仍然是一个悬而未决的问题。最近的研究表明活动星系核可以调节气体吸积,从而减缓恒星的形成(负反馈)。然而,活动星系核正反馈的证据也在一些射电星系中被观察到(例如。半人马座A)。在这里,我们提出的CO观测3C 285和闵可夫斯基对象(MO),这是喷流诱导恒星形成的例子。与3C 285射电喷流对齐的一个点(命名为09.6),距离星系中心约70千秒差距,显示了恒星的形成,在光学发射中检测到。MO位于NGC 541的喷流附近,也显示了恒星的形成。了解分子气体沿喷流的分布是研究活动星系核与星系际介质相互作用中物理过程的一个重要途径。我们用IRAM-30 m望远镜观测了3C 285、NGC 541、09.6和MO中的CO谱线。在中央星系,光谱提出了一个双喇叭的配置文件,典型的旋转模式,从我们能够估计的分子气体密度分布的星系。分子气体似乎在一个致密的储层中。此外,30米望远镜没有检测到分子外流的运动学特征。有趣的是,09.6和MO中没有检测到CO。冷气体质量上限是一致的,与致密的周围物质的压缩所引起的恒星形成的射流。耗尽时间尺度与3C 285、NGC 541和本星系旋涡星系(10^9年)相当,甚至更小。如果发射区域非常紧凑,则09.6中的分子气体表面密度遵循施密特-肯尼库特定律,而MO被发现具有高得多的SFE(非常短的耗尽时间)。更高的灵敏度和空间分辨率是必要的,以检测CO在恒星形成的斑点,并映射在这些喷流诱导的恒星形成区域的排放。

英文摘要:

How efficiently star formation proceeds in galaxies is still an open question. Recent studies suggest that AGN can regulate the gas accretion and thus slow down star formation (negative feedback). However, evidence of AGN positive feedback has also been observed in a few radio galaxies (eg. Centaurus A). Here we present CO observations of 3C 285 and Minkowski Object (MO), which are examples of jet-induced star formation. A spot (named 09.6) aligned with the 3C 285 radio jet, at a projected distance of ~70 kpc from the galaxy centre, shows star formation, detected in optical emission. MO is located along the jet of NGC 541 and also shows star formation. To know the distribution of molecular gas along the jets is a way to study the physical processes at play in the AGN interaction with the intergalactic medium. We observed CO lines in 3C 285, NGC 541, 09.6 and MO with the IRAM-30m telescope. In the central galaxies, the spectra present a double-horn profile, typical of a rotation pattern, from which we are able to estimate the molecular gas density profile of the galaxy. The molecular gas appears to be in a compact reservoir. In addition, no kinematic signature of a molecular outflow is detected by the 30m-telescope. Interestingly, 09.6 and MO are not detected in CO. The cold gas mass upper limits are consistent with a star formation induced by the compression of dense ambient material by the jet. The depletion time scales are of the order of and even smaller than what is found in 3C 285, NGC 541 and local spiral galaxies (10^9 yr). The molecular gas surface density in 09.6 follows a Schmidt-Kennicutt law if the emitting region is very compact, while MO is found to have a much higher SFE (very short depletion time). Higher sensitivity and spatial resolution are necessary to detect CO in the spots of star formation, and map the emission in these jet-induced star forming regions.

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