Discovery of Dying Active Galactic Nucleus in Arp 187: Experience of Drastic Luminosity Decline within 104 yr
Discovery of Dying Active Galactic Nucleus in Arp 187: Experience of Drastic Luminosity Decline within 104 yr
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DOI：
10.3847/1538-4357/aaf233
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发表时间：
2018-11
期刊：
影响因子：
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通讯作者：
K. Ichikawa;J. Ueda;Hyun-Jin Bae;T. Kawamuro;K. Matsuoka;Y. Toba;M. Shidatsu
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作者：
K. Ichikawa;J. Ueda;Hyun-Jin Bae;T. Kawamuro;K. Matsuoka;Y. Toba;M. Shidatsu
阿普187是一个衰落的活动星系核，其活动星系核的亮度目前正在下降。我们研究了活动星系核在阿普187的观测特征，追踪了从小于0.1秒差距到近10千秒差距的各种物理尺度，估计了104年的长期光度变化。甚大阵5 GHz和8 GHz的图像和阿尔马133 GHz的图像揭示了双峰喷流瓣的大小为1.5 kpc和缺乏中央无线电核心。6dF光谱显示阿普187有一个窄的谱线区域，其大小估计为1.01 kpc，谱线强度给出活动星系核的亮度为Lbol = 1.5 × 1046 erg s−1。另一方面，根据活动星系核环的发射估算出的活动星系核活动的上限为Lbol < 2.2 × 1043 erg s−1。射电核心的缺失给出了目前活动星系核光度的更严格上限Lbol < 8.0 × 1040 erg s−1，表明中心引擎已经熄灭。这些多波长特征表明，阿普187拥有一个“垂死”的活动星系核：中心引擎已经死亡，但大规模的活动星系核指标仍然是可观测到的，作为过去活动星系核活动的残余。中心发动机在1004年内经历了亮度衰减1003 -5倍的剧烈变化，这与吸积盘内部的粘性时标在1500年内大致一致。
Arp 187 is one of the fading active galactic nuclei (AGNs), whose AGN activity is currently decreasing in luminosity. We investigate the observational signatures of AGN in Arp 187, which trace various physical scales from less than 0.1 pc to the nearly 10 kpc, to estimate the long-term luminosity change over 104 yr. The Very Large Array 5 GHz and 8 GHz images and the ALMA 133 GHz images reveal bimodal jet lobes with ∼5 kpc size and the absence of the central radio core. The 6dF optical spectrum shows that Arp 187 hosts a narrow line region with the estimated size of ∼1 kpc, and the line strengths give the AGN luminosity of Lbol = 1.5 × 1046 erg s−1. On the other hand, the current AGN activity estimated from the AGN torus emission gives the upper bound of Lbol < 2.2 × 1043 erg s−1. The absence of the radio core gives the more strict upper bound of the current AGN luminosity of Lbol < 8.0 × 1040 erg s−1, suggesting that the central engine is already quenched. These multiwavelength signatures indicate that Arp 187 hosts a “dying” AGN: the central engine is already dead, but the large-scale AGN indicators are still observable as the remnant of the past AGN activity. The central engine has experienced the drastic luminosity decline by a factor of ∼103–5 fainter within ∼104 yr, which is roughly consistent with the viscous timescale of the inner part of the accretion disk within ∼500 yr.