遗迹放射性镓的光谱特性研究
Exploring the spectroscopic properties of relic radiogalaxies
摘要：
通过对z<0.3的3CR射电星系（RGs）的光谱测量，我们发现了三个具有极低气体激发水平和相对于类似射电光度的RGs而言线发射的大缺陷的天体。我们将这些天体解释为遗留的活动星系核（AGN），即，在其核活动大幅下降后观察到的来源。在这里，我们提出了新的光谱观测这三个星系和一组“候选人”的遗物。没有一个候选人能得到令人信服的确认。根据这三个遗迹的新数据，我们估计了线发射气体的密度。这使我们能够探索活动星系核“死亡”后谱线比的时间演化。特征时间尺度是发射线区域的光穿越时间，几千年，太短，无法对应大量的遗迹RG。气体电离的其他机制，如“遗迹冲击”，从他们过去的高功率阶段或恒星源，也应考虑占遗迹RG的光谱特性。遗迹RG似乎是不同演化阶段的混合源，包括最近（约10，000年前）熄灭的AGN，至少100万年不活动的星系，以及从强大的RG到低功率FRI源过渡期间捕获的对象。
英文摘要：
From an optical spectroscopic survey of 3CR radiogalaxies (RGs) with z<0.3, we discovered three objects characterized by an extremely low level of gas excitation and a large deficit of line emission with respect to RGs of similar radio luminosity. We interpreted these objects as relic active galactic nuclei (AGN), i.e., sources observed after a large drop in their nuclear activity. We here present new spectroscopic observations for these three galaxies and for a group of "candidate" relics. None of the candidates can be convincingly confirmed. From the new data for the three relics, we estimate the density of the line-emitting gas. This enables us to explore the temporal evolution of the line ratios after the AGN "death". The characteristic timescale is the light-crossing time of the emission line region, a few thousand years, too short to correspond to a substantial population of relic RGs. Additional mechanisms of gas ionization, such as "relic shocks" from their past high power phase or stellar sources, should also be considered to account for the spectroscopic properties of the relic RGs. Relic RGs appear to be a mixed bag of sources in different phases of evolution, including AGN recently (~10,000 years ago) quenched, galaxies that have been inactive for at least one million years, and objects caught during the transition from a powerful RG to a low power FRI source.
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