射电噪活动星系核的光度函数与演化研究

发布时间：2018-01-15 14:01

本文关键词：射电噪活动星系核的光度函数与演化研究　出处：《中国科学院研究生院（云南天文台）》2013年博士论文　论文类型：学位论文

【摘要】：射电噪活动星系核（radio-loud AGN）是宇宙中的强射电源，常将这类天体分为平谱源和陡谱源，按照AGN的统一模型，它们的差异很大程度上源于倾角的不同，两类源都可以用“致密核+喷流+延展射电瓣”的图像来描述。在传统的方法中，人们通过独立地研究陡谱源和平谱源的射电光度函数来获得它们的演化信息。然而，由于AGN射电辐射和活动本身的特点，例如延展性、方向性、间歇性等，使得传统方法获得的信息比较有限。随着射电观测精度的日益提高，已观测到大量的射电核，射电核的存在是AGN射电活动性很好的指示。本论文利用现有的观测资料，研究了射电核的光度函数。由于射电核处在AGN的中心位置，对其光度函数的研究，可以更直接地探究AGN中心区域物质吸积与喷流的关系。首先我们通过文献查阅和数据库检索，建立了一个包含1063个源的陡谱射电噪活动星系核样本，基于此样本，用1/Va方法计算了这类射电源在408MHz处的射电光度函数，我们的结果支持一个光度依赖的密度演化模式。大多数源的射电核有5GHz处的流量密度数据，利用这些数据我们又计算了射电核在5GHz处的光度函数。结果表明射电核的共动数密度是随红移增加而逐渐减小的，即呈现出一种负宇宙演化模式。对此结果，一个很好的解释是：在AGN早期，吸积率可能较高，反而不利于jet的射电辐射，甚至于jet的产生，在AGN中可能也有类似于X射线双星的“软”态和“硬”态的演化。我们的结果与前人从不同角度所得到的结论也是一致的。我们还注意到射电核的光度函数与源的总射电光度函数形式完全不同，由于我们样本的源都是瓣主导的陡谱源，这说明核和瓣并不是协同演化的。此外，我们回顾了经典的、用于估计光度函数的1/Va方法，以及PC方法，并通过图像分析的方法对二者做了比较。通过理论分析和实例证明，我们指出了两种方法对于那些被极限流量曲线L=Llim(z)穿过的小间隔（bin）总是会给出不同估计的原因之所在。基于一个由蒙特卡洛方法模拟出的虚拟样本，我们比较了两种方法给出的估计与输入模型值的差异。结果发现，两种方法对高光度的那些bin给出的估计完全相同而且比较理想，但是对低光度的那些bin，两者给出的估计都显著地低于输入模型值。我们认为，只要光度函数沿着红移有演化，那么传统的、需要划分间隔的非参数方法就不可能在整个光度区间都给出理想的估计。前人注意到对于光度函数的暗端，1/Va给出的结果总是太小，从而认为PC方法要优于1/Va方法。实际上这只是由于随意选取bin的缘故。我们提出了一种简单有效的选择bin的方法，运用此方法，可以对两种方法的结果都有不同程度的改进。经过改进后，，很难说PC方法的结果要比1/Va方法的更优越。
[Abstract]:Radio-loud AGNN (Radio-loud AGNN) is a powerful radio source in the universe. It is often classified as a flat spectral source and a steep spectral source, according to the unified model of AGN. Their differences are largely due to different dip angles, and both types of sources can be described by images of "dense nuclear jet extended radio lobes." in traditional methods. The evolution information is obtained by studying the radio luminosity functions of steep spectral sources and spectral sources independently. However, due to the characteristics of AGN radio radiation and activity itself, such as ductility, directionality, intermittency, etc. With the increasing accuracy of radio observation, a large number of radio cores have been observed. The existence of radio nuclei is a good indication of the radio activity of AGN. In this paper, the luminosity function of radio nuclei is studied by using the available observation data. Because the radio nuclei are located at the center of AGN. The study of its luminosity function can more directly explore the relationship between mass accretion and jet flow in the central region of AGN. Firstly, we establish a steep-spectrum radio noised active galactic nucleus (AGNs) sample containing 1063 sources based on literature review and database retrieval. The radio luminosity function of this kind of radio source at 408 MHz is calculated by using the 1 / V a method. Our results support a photometric dependent density evolution model. Most source radio cores have flow density data at 5GHz. Using these data, we calculate the luminosity function of the radio nucleus at 5GHz. The results show that the density of the coaction number of the radio nucleus decreases with the increase of the red shift. A good explanation for this result is that the accretion rate may be higher in the early stage of AGN, which is not conducive to the radio radiation of jet, even to the production of jet. There may also be "soft" and "hard" states similar to X-ray binaries in AGN. Our results are consistent with the previous conclusions from different angles. We also note that the photometric function of the radio nucleus is completely different from the total radio photometric function of the source. Since the source of our sample is a petal-dominated steep spectrum source, this indicates that the kernel and lobe are not coevolved. In addition, we review the classical 1 / Va method used to estimate the photometric function and the PC method, and compare them with the image analysis method. We point out two methods for small interval bindings that are crossed by the limit flow curve Ln Llimz). The reasons for different estimates are always given based on a virtual sample simulated by the Monte Carlo method. We compare the differences between the estimates given by the two methods and the values of the input model. The results show that the estimates given by the two methods for those bin with high luminosity are identical and ideal. But for those bines with low luminosity, both estimates are significantly lower than the input model values. We think that as long as the photometric function evolves along the redshift, then the tradition is. It is impossible to give an ideal estimate in the whole luminosity region by the nonparametric method which needs to divide the interval. It has been noted that the results given for the dark end of the photometric function 1 / V a are always too small. It is concluded that the PC method is better than the 1 / V a method. In fact, this is only due to the random selection of bin. We propose a simple and effective method to select bin, and use this method. After improvement, it is difficult to say that the result of PC method is better than that of 1 / V a method.
【学位授予单位】：中国科学院研究生院（云南天文台）
【学位级别】：博士
【学位授予年份】：2013
【分类号】：P157.6;P161

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