arXiv 2008.109692020-08-25astro-ph.GA

VLA-COSMOS 3 GHz大型项目：活动星系核的平均射电频谱能量分布

The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of active galactic nuclei

Krešimir Tisanić, V. Smolčić, M. Imbrišak, M. Bondi, G. Zamorani, L. Ceraj, E. Vardoulaki, J. Delhaize

备注：: 12 pages, 11 figures
发表信息：: A&A 643, A51 (2020)
DOI：: 10.1051/0004-6361/201937114

摘要：

由于SKA预计将在未来十年内投入使用，因此对100 MHz至10 GHz范围内的无线电天空的调查对于SKA观测的模拟变得非常重要。在从射电数据确定星系的物理性质时，射电SED通常被假设为由简单的幂律描述，通常所有源的光谱指数为0.7。尽管无线电SED已被证明表现出偏离这一假设，无论是在不同的频谱指数和复杂的频谱形状，它通常被认为是他们的个体差异抵消了大样本。我们构造了射电过剩活动星系核（RxAGN）的平均射电SED，定义为那些表现出3 $σ$射电光度过剩的值，预期只有从恒星形成的贡献，到z~4。我们结合了在1.4 GHz和3 GHz的COSMOS场的VLA观测与在325 MHz和610 MHz的GMRT观测。为了解释GMRT图中的未检测，我们采用了生存分析技术。我们选择了一个样本的RxAGN到z~4。我们发现，一个样本的RxAGN可以描述的频谱指数为$α_1=0.28\pm0.03$低于断裂频率$ν_b=(4.1\pm0.2)$ GHz和$α_2=1.16\pm0.04$以上，而一个简单的幂律模型产生一个单一的频谱指数$α=0.64\pm0.07$。通过对1.4 GHz射电光度和红移的分箱，我们发现，幂律谱指数和破幂律谱指数随源尺寸的增大而增大，而幂律谱指数和低频（<4 GHz）破幂律谱指数与红移也呈正相关。

英文摘要：

As the SKA is expected to be operational in the next decade, investigations of the radio sky in the range of 100 MHz to 10 GHz have become important for simulations of the SKA observations. In determining physical properties of galaxies from radio data, the radio SED is often assumed to be described by a simple power law, usually with a spectral index of 0.7 for all sources. Even though radio SEDs have been shown to exhibit deviations from this assumption, both in differing spectral indices and complex spectral shapes, it is often presumed that their individual differences cancel out in large samples. We constructed the average radio SED of radio-excess active galactic nuclei (RxAGN), defined as those that exhibit a 3 $σ$ radio luminosity excess with respect to the value expected only from contribution from star formation, out to z~4. We combined VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with GMRT observations at 325 MHz and 610 MHz. To account for nondetections in the GMRT maps, we employed the survival analysis technique. We selected a sample of RxAGN out to z~4. We find that a sample of RxAGN can be described by a spectral index of $α_1=0.28\pm0.03$ below the break frequency $ν_b=(4.1\pm0.2)$ GHz and $α_2=1.16\pm0.04$ above, while a simple power-law model yields a single spectral index of $α=0.64\pm0.07$. By binning in 1.4 GHz radio luminosity and redshift, we find that the power-law spectral index, as well as broken power-law spectral indices, may increase for larger source sizes, while the power-law spectral index and lower-frequency (<4 GHz) broken power-law spectral index are additionally positively correlated with redshift.

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英文摘要：

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