[论文解读] Deceleration of Relativistic Radio Components and the morphologies of Gigahertz Peaked Spectrum Sources

I. A. G. Snellen, R. T. Schilizzi+2 more|University of Groningen research database (University of Groningen / Centre for Information Technology)|Jan 29, 1998

Radio Astronomy Observations and Technology被引用 3

一句话总结

本文提出，吉赫兹峰值谱（GPS）源的紧凑、凸谱形态源于从星系核以大角度喷出的相对论性射电组分，这些组分在外部气体中因阻尼压或卷吸作用而减速。随着这些组分减速，其沿运动方向的流量密度因多普勒增强而增加，形成非相对论性迷你瓣，主导了观测到的辐射，从而解释了GPS源的低变异性、紧凑双瓣结构以及凸谱特征。

ABSTRACT

A relativistic radio component, which moves in a direction close to the sky plane, will increase in flux density when it decelerates. This effect is the basis for the qualitative model for GPS galaxies we present in this paper, which can explain their low-variability convex spectrum, their compact double or compact symmetric morphology, and the lack of GPS quasars at similar redshifts. Components are expelled from the nucleus at relativistic speeds at a large angle to the line of sight, and are decelerated (eg. by ram-pressure or entrainment of the external gas) before contributing to a mini-lobe. The young components are Doppler boosted in the direction of motion but appear fainter for the observer. The non-relativistic mini-lobes dominate the structure and are responsible for the low variability in flux density and the convex radio spectrum as well as the compact double angular morphology. Had the same source been orientated at a small angle to the line of sight, the young components would be boosted in the observer's direction resulting in a flat and variable radio spectrum at high frequencies. Hence the characteristic convex spectrum of a GPS source would not be seen. These sources at small angles to the line of sight are probably identified with quasars, and are not recognized as GPS sources, but are embedded in the large population of flat spectrum variable quasars and BL Lac objects. This leads to a deficiency in GPS/CSOs identified with quasars.

研究动机与目标

• 解释吉赫兹峰值谱（GPS）源的紧凑双瓣形态及其低变异性。
• 通过关联取向与相对论性束状效应，解决GPS源在电波源中数量不足的问题。
• 通过减速相对论性组分的动力学解释GPS源中的凸射电谱。
• 解释尽管具有相似本征性质，GPS源为何未被观测为平坦谱、可变的电波星。
• 将从相对论性喷流到非相对论性迷你瓣的演化建模为观测射电形态的起源。

提出的方法

• 建模从活动星系核以大角度喷出的相对论性射电组分。
• 应用多普勒增强以解释组分在减速过程中沿运动方向的流量密度增强。
• 引入阻尼压或卷吸力以模拟相对论性组分在外部介质中的减速过程。
• 模拟从相对论性组分到非相对论性迷你瓣的射电辐射演化。
• 比较源以大角度与小角度取向时的光谱与形态特性。
• 利用谱指数演化解释GPS源中观测到的凸谱特征，以及电波星中的平坦谱特征。

实验结果

研究问题

• RQ1 为何GPS源表现出紧凑的双瓣形态且变异性低？
• RQ2 何种物理机制导致GPS源中特有的凸射电谱？
• RQ3 尽管红移相似，为何GPS源未被观测为平坦谱、可变的电波星？
• RQ4 源相对于视线方向的取向如何影响其观测光谱与形态特性？
• RQ5 相对论性组分的减速在塑造GPS源观测射电结构中起何种作用？

主要发现

• 由于阻尼压或卷吸作用导致的相对论性射电组分减速，使其沿运动方向的流量密度因多普勒增强而增加。
• 减速后形成的非相对论性迷你瓣主导了观测辐射，导致紧凑双瓣形态。
• GPS源的凸射电谱源于减速组分及其非相对论性残余物的辐射叠加。
• 以小角度取向的源由于强多普勒增强会表现出平坦且可变的光谱，因此被识别为电波星或BL Lacs天体。
• GPS电波星的缺失可通过以下事实解释：此类源因平坦且可变的光谱而不被识别为GPS源。
• 该模型通过将光谱与形态特性与源取向及组分减速相联系，解释了在电波星中观测不到GPS源的原因。