FIRST “Winged” and X-Shaped Radio Source Candidates
FIRST “Winged” and X-Shaped Radio Source Candidates
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DOI：
10.1086/513095
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
C. Cheung
中科院分区：
文献类型：
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作者：
C. Cheung
少数双瓣射电星系（根据我们自己的文献普查有 17 个）显示出一对额外的低表面亮度“翅膀”，从而形成整体 X 形外观。这些无线电源中翅膀的起源尚不清楚。它们可能是等离子体从当前活跃的射电波瓣回流到活跃核周围的不对称介质中的结果，这将使这些系统成为研究河外无线电源中的热/非热等离子体相互作用的理想系统。另一种可能性是，翅膀是中央超大质量黑洞吸积盘系统（可能由于合并）（快速）重新排列后留下的老化射电波瓣。一般来说，这些模型没有经过充分的测试；由于已知的例子数量较少，以前的工作都集中于对选定来源的详细案例研究，很少尝试对大样本进行系统研究。使用 VLA FIRST 调查数据库，我们正在为此类研究编制大量翼状和 X 形无线电源样本。作为实现这一目标的第一步，本文提出了 100 个此类新候选对象的初始样本。描述了搜索过程，并提出了现有文献数据和基本无线电数据的光学识别。从有限分辨率的 FIRST 图像 (∼5") 中，我们已经可以自信地将足够数量的此类物体分类为具有 >80% 活动波瓣的特征翼长度，是已知 X 形射电源数量的两倍以上。我们还包括了具有较短机翼（<80% 机翼与波瓣长度比）或简单的“有翼”源的候选无线电源，因为投影效应可能很重要。最后，候选者中有四个类星体（z = 0.37-0.84），其中几个类星体的形态暗示着 Fanaroff-Riley I 型（低功率）射电星系。虽然需要进行后续观察来确认这些识别，但这强调了源方向和成像限制在寻找这些神秘物体时的重要性。
A small number of double-lobed radio galaxies (17 from our own census of the literature) show an additional pair of low surface brightness "wings," thus forming an overall X-shaped appearance. The origin of the wings in these radio sources is unclear. They may be the result of backflowing plasma from the currently active radio lobes into an asymmetric medium surrounding the active nucleus, which would make these ideal systems in which to study thermal/nonthermal plasma interactions in extragalactic radio sources. Another possibility is that the wings are the aging radio lobes left over after a (rapid) realignment of the central supermassive black hole-accretion disk system due perhaps to a merger. Generally, these models are not well tested; with the small number of known examples, previous works have focused on detailed case studies of selected sources with little attempt at a systematic study of a large sample. Using the VLA FIRST survey database, we are compiling a large sample of winged and X-shaped radio sources for such studies. As a first step toward this goal, an initial sample of 100 new candidate objects of this type are presented in this paper. The search process is described, and optical identifications from available literature data and basic radio data are presented. From the limited-resolution FIRST images (∼5″), we can already confidently classify a sufficient number of these objects as having the characteristic wing lengths of >80% of the active lobes to more than double the number of known X-shaped radio sources. We have also included as candidates radio sources with shorter wings (<80% wing-to-lobe length ratios), or simply "winged" sources, as it is probable that projection effects are important. Finally, among the candidates are four quasars (z = 0.37-0.84), and several have morphologies suggestive of Fanaroff-Riley type I (low-power) radio galaxies. While follow-up observations are necessary to confirm these identifications, this stresses the importance of source orientation and imaging limitations in finding these enigmatic objects.