[论文解读] Thermal and Nonthermal Radio Galaxies

Robert Antonucci|arXiv (Cornell University)|Jan 4, 2011

Galaxies: Formation, Evolution, Phenomena被引用 9

一句话总结

本文确立了射电星系的基本二分法：一类具有可检测的热辐射（吸积驱动，类夸克星），另一类则由非热喷流动能主导，尤其在低射电光度时更为显著。研究结论指出，仅最明亮的FRII、GPS和CSS射电星系才拥有隐藏的类星体，而大多数低光度源为非热型，不存在显著的吸积盘或宽发射线。

ABSTRACT

Radio galaxies were discovered and mapped in the 1950s. The optical spectra showed little or no nuclear continuum light. Some also revealed powerful high ionization emission lines, while others showed at most weak low-ionization emission lines. Quasars were found in the 1960s, and their spectra were dominated by powerful continuum radiation which was subsequently identified with optically thick thermal radiation from copious accretion flows, as well as high ionization narrow emission lines, and powerful broad permitted lines. By the 1980s, data from optical polarization and statistics of the radio properties required that many radio galaxies contain hidden quasar nuclei, hidden from the line of sight by dusty, roughly toroidal gas distributions. The radio galaxies with hidden quasars are referred to as "thermal." Do all radio galaxies have powerful hidden quasars? We now know the answer using arguments based on radio, infrared, optical and X-ray properties. Near the top of the radio luminosity function, for FRII, GPS, and CSS galaxies, the answer is yes. Below the top of the radio luminosity function, many do not. At low radio luminosities, most do not. Instead these "nonthermal" weakly-accreting galaxies are powerful emitters of kinetic energy in the form of synchrotron jets. They generally have weak low-ionization lines. This applies to all types of radio galaxy, big FR II doubles, as well as the small young GigaHertz-Peaked-Spectrum and Compact Steep Spectrum sources. Only a few FR I sources are of the thermal type.

研究动机与目标

• 基于多波段特性，厘清热型与非热型射电星系之间的区别。
• 解决长期以来关于所有射电星系是否均拥有隐藏类星体的疑问。
• 确立在低射电光度下非热型射电星系占主导地位，尤其在FR I和低光度FRII源中。
• 在非热源普遍存在的背景下，重新评估活动星系核统一模型。

提出的方法

• 分析一个广泛样本的射电星系在射电、红外、光学和X射线波段的数据。
• 利用谱谱能量分布识别‘蓝峰’特征，以指示热吸积的存在。
• 通过比较光学谱线特性（低电离与高电离、宽线与窄线）推断隐藏宽线区的存在与否。
• 应用统一模型原则，将源分类为I型（宽线）或II型（窄线），重点关注被遮蔽的类星体。
• 评估X射线与红外诊断指标，以探测康普顿厚吸收及隐藏活动星系核。
• 利用VLBI与大尺度射电形态分析，评估喷流特性及其与喷流主导反馈的一致性。

实验结果

研究问题

• RQ1 所有射电星系是否如统一模型所暗示的那样，均拥有隐藏类星体？
• RQ2 低光度射电星系中，有多少比例表现出热辐射（吸积驱动）发射，又有多少比例表现出非热辐射（喷流主导）发射？
• RQ3 射电星系的谱和形态特性如何与它们的射电光度及吸积状态相关联？
• RQ4 非热型射电星系在多大程度上缺乏可检测的吸积盘和宽发射线？
• RQ5 热态与非热态之间的转变是否可与爱丁顿比或吸积模式相关联？

主要发现

• 仅最亮的FRII、GPS和CSS射电星系（接近射电光度函数顶端）拥有隐藏类星体。
• 在低射电光度下，大多数射电星系为非热型，既无明显‘蓝峰’也无宽发射线。
• FR I源主要为非热型，仅有少数例外表现出热特性。
• 大多数低电离、窄线射电星系为非热型，既缺乏热吸积盘，也缺乏宽线区。
• 从热型向非热型转变发生在光度低于~0.01 L_Edd时，与ADAF吸积模型一致。
• 耀变体并非FR I源的母体种群，且部分BL Lacs中存在FR II型射电瓣并非与统一模型矛盾。