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arXiv 1502.00427astro-ph.GA
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射电发射AGN星群的初步研究:新出现的FR0射电星系

A pilot study of the radio-emitting AGN population: the emerging new class of FR0 radio-galaxies

Ranieri D. Baldi, Alessandro Capetti, Gabriele Giovannini

摘要:

本文介绍了一个JVLA试验项目的结果,该项目旨在研究由NVSS/FIRST和SDSS巡天所揭示的大部分射电活动星系核,我们在JVLA获得了1.4,4.5和7.5 GHz的SDSS/NVSS样品的12个源的A-阵列观测。射电图显示了1 - 3千秒差距尺度上的致密的未分辨或略分辨的射电结构,只有一个例外,即一个FRI/FRII源延伸超过$\sim$ 40千秒差距。我们分离了大多数的无线电核心部件。样本分为两组。有四个来源有小黑洞(BH)质量(大多数是$\sim$ 10 $^{7}$ M $_{\odot}$),并由蓝色星系托管,经常显示出从恒星形成到其射电辐射的污染证据,并与无线电安静的活动星系核有关。第二组由7个射电强活动星系核组成,它们生活在红色大质量($\sim10^{11}$ M $_{\odot}$)的早型星系中,具有大BH质量($\gtrsim$ 10 $^{8}$ M $_{\odot}$),光谱分类为低激发星系,所有特征都是FRI射电星系的典型特征。它们也依赖于FRIs定义的射电核心功率和[O III]线光度之间的相关性。然而,它们比FRIs更受核心支配(因子为$\sim$ 30),并表现出扩展射电发射的不足。我们称这些源为"FR 0",以强调它们缺乏突出的扩展无线电发射,相对于FRIs的唯一区别特征。FR 0和FRIs之间的无线电特性的差异可能归因于进化效应,FR 0源经历快速的不稳定性,防止大尺度结构的生长。在我们的首选方案中,FR 0中缺乏扩展的无线电发射是由于它们相对于FRI较小的喷流洛伦兹$Γ$因子,从而导致可能的不稳定性和过早的破坏。[删节]

英文摘要:

We present the results of a pilot JVLA project aimed at studying the bulk of the radio-emitting AGN population, unveiled by the NVSS/FIRST and SDSS surveys.We obtained A-array observations at the JVLA at 1.4, 4.5, and 7.5 GHz for 12 sources of the SDSS/NVSS sample. The radio maps reveal compact unresolved or slightly resolved radio structures on a scale of 1-3 kpc, with only one exception of a FRI/FRII source extended over $\sim$40 kpc. We isolate the radio core component in most of them. The sample splits into two groups. Four sources have small black hole (BH) masses (mostly $\sim$10$^{7}$ M$_{\odot}$) and are hosted by blue galaxies, often showing evidence of a contamination from star formation to their radio emission and associated with radio-quiet AGN. The second group consists in seven radio-loud AGN, which live in red massive ($\sim10^{11}$ M$_{\odot}$) early-type galaxies, with large BH masses ($\gtrsim$10$^{8}$ M$_{\odot}$), and spectroscopically classified as Low Excitation Galaxies, all characteristics typical of FRI radio galaxies. They also lie on the correlation between radio core power and [O III] line luminosity defined by FRIs. However, they are more core dominated (by a factor of $\sim$30) than FRIs and show a deficit of extended radio emission. We dub these sources 'FR0' to emphasize their lack of prominent extended radio emission, the single distinguishing feature with respect to FRIs. The differences in radio properties between FR0s and FRIs might be ascribed to an evolutionary effect, with the FR0 sources undergoing to rapid intermittency that prevents the growth of large scale structures. In our preferred scenario the lack of extended radio emission in FR0s is due to their smaller jet Lorentz $Γ$ factor with respect to FRIs, causing possible instabilities and their premature disruption.[abridged]

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