X型射电星系的起源
On the origin of X-shaped radio galaxies
摘要：
经过简短的，批判性的审查，提出了一个小的，但重要的射电星系子集的X形形态（XRGs）的主要解释，我们提出了一个广义的模型，基于喷壳相互作用和自旋翻转假说。对于这种有趣的现象，最流行的情景是流体动力学回流和过压茧或快速喷流重新定向，大概是由于星系对合并后中央引擎的自旋翻转，每个星系都包含一个超大质量黑洞（SMBH）。我们面对这些模型与一些关键的意见，从而认为，没有一个模型是能够解释整个范围内的显着的观测特性的XRGs，虽然在文献中提出的一些论点反对自旋翻转的情况可能是站不住脚的。然后，我们在这里提出了一个新的方案，其中也涉及星系合并，但将允许旋转的中央引擎，以保持其方向。受最近的射电星系半人马座A的详细多波段观测的启发，这个新模型强调了喷流与恒星和气体外壳之间的相互作用，这些外壳围绕合并的星系形成和旋转，并可能导致喷流的暂时偏转，偶尔会产生X形射电结构。虽然每个模型都可能与XRG的一个子集相关，但大量证据表明，其中大多数都可以用喷流-壳层相互作用或自旋翻转假说来解释。
英文摘要：
After a brief, critical review of the leading explanations proposed for the small but important subset of radio galaxies showing an X-shaped morphology (XRGs) we propose a generalized model, based on the jet-shell interaction and spin-flip hypotheses. The most popular scenarios for this intriguing phenomenon invoke either hydrodynamical backflows and over-pressured cocoons or rapid jet reorientations, presumably from the spin-flips of central engines following the mergers of pairs of galaxies, each of which contains a supermassive black hole (SMBH). We confront these models with a number of key observations and thus argue that none of the models is capable of explaining the entire range of salient observational properties of XRGs, although some of the arguments raised in the literature against the spin-flip scenario are probably not tenable. We then propose here a new scenario which also involves galactic mergers but would allow the spin of the central engine to maintain its direction. Motivated by the detailed multi-band observations of the nearest radio galaxy, Centaurus A, this new model emphasizes the role of interactions between the jets and the shells of stars and gas that form and rotate around the merged galaxy and can cause temporary deflections of the jets, occasionally giving rise to an X-shaped radio structure. Although each of the models is likely to be relevant to a subset of XRGs, the bulk of the evidence indicates that most of them are best explained by the jet-shell interaction or spin-flip hypotheses.
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