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arXiv 1607.03709astro-ph.GA
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15.7 GHz处的微弱源群- III。HERG和LERG的高频研究

The faint source population at 15.7 GHz - III. A high-frequency study of HERGs and LERGs

Imogen H. Whittam, Julia M. Riley, David A. Green, Matt J. Jarvis

摘要:

从第十次剑桥巡天(10 C)15.7~GHz观测中选取了96个暗($S > 0.5$ mJy)射电星系的完整样本。光谱被用来分类17个来源的高激发或低激发射电星系(HERG和LERG分别),其余的来源使用其他三种方法,这些是光学致密性,X射线观测和中红外彩色-彩色图。32个来源是HERG,35个是LERG,其余29个来源无法分类。我们发现,10 C HERG往往有更高的15.7 GHz的通量密度,平坦的光谱,较小的线性尺寸,并发现在更高的红移比LERG。这表明10 C HERG比LERG更受核心支配。低频无线电图像,线性大小和频谱指数被用来分类的来源,根据其无线电形态; 18 Fanaroff和莱利I型或II源,进一步13个显示一些扩展的发射,其余65个源是紧凑的,被称为FR 0源。FR 0源被细分为紧凑,陡谱(CSS)源(13个源)或GHz峰值频谱(GPS)源(10个源),其余42个在未分类的类。FR 0源在15.7 GHz通量密度$<$ 1 mJy的源子集中更占主导地位,这与先前的结果一致,即较暗的10 C源具有较平坦的无线电频谱。10 C源的属性进行了比较,以更高的通量密度澳大利亚望远镜20 GHz(AT 20 G)的调查。10 C源的红移与AT 20 G源相似,但亮度较低。高频选定物体的性质随着通量密度的降低而改变;在高通量密度下,物体主要是类星体,而在低通量密度下,射电星系占主导地位。

英文摘要:

A complete sample of 96 faint ($S > 0.5$ mJy) radio galaxies is selected from the Tenth Cambridge (10C) survey at 15.7~GHz. Optical spectra are used to classify 17 of the sources as high-excitation or low-excitation radio galaxies (HERGs and LERGs respectively), for the remaining sources three other methods are used; these are optical compactness, X-ray observations and mid-infrared colour--colour diagrams. 32 sources are HERGs and 35 are LERGs while the remaining 29 sources could not be classified. We find that the 10C HERGs tend to have higher 15.7-GHz flux densities, flatter spectra, smaller linear sizes and be found at higher redshifts than the LERGs. This suggests that the 10C HERGs are more core dominated than the LERGs. Lower-frequency radio images, linear sizes and spectral indices are used to classify the sources according to their radio morphology; 18 are Fanaroff and Riley type I or II sources, a further 13 show some extended emission, and the remaining 65 sources are compact and are referred to as FR0 sources. The FR0 sources are sub-divided into compact, steep-spectrum (CSS) sources (13 sources) or GHz-peaked spectrum (GPS) sources (10 sources) with the remaining 42 in an unclassified class. FR0 sources are more dominant in the subset of sources with 15.7-GHz flux densities $<$1 mJy, consistent with the previous result that the fainter 10C sources have flatter radio spectra. The properties of the 10C sources are compared to the higher-flux density Australia Telescope 20 GHz (AT20G) survey. The 10C sources are found at similar redshifts to the AT20G sources but have lower luminosities. The nature of the high-frequency selected objects change as flux density decreases; at high flux densities the objects are primarily quasars, while at low flux densities radio galaxies dominate.

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