2026-03-24 自然科学研究機構
図１：100 億光年（赤方偏移 1.8）の距離にある銀河 J0218-0036（黄色矢印）の可視光画像。（クレジット：SDSS、HSC-SSP/国立天文台）
＜関連情報＞
- https://subarutelescope.org/jp/results/2026/03/24/3687.html
- https://academic.oup.com/pasj/article/77/6/1350/8313806
z ∼ 1.8の活動銀河核における質量降着の停止事象の可能性 A possible shutting-down event of mass accretion in an active galactic nucleus at z ∼ 1.8
Tomoki Morokuma ,Malte Schramm ,Toshihiro Kawaguchi ,Josefa Becerra González ,Jose Antonio Acosta-Pulido ,Nieves Castro-Rodríguez ,Kana Morokuma-Matsui ,Shintaro Koshida ,Junko Furusawa ,Hisanori Furusawa,…
Publications of the Astronomical Society of Japan Published:04 November 2025
DOI:https://doi.org/10.1093/pasj/psaf115
Abstract
We present the discovery of a large gradual apparent fading event in optical and near-infrared wavelengths in a quasar at by a factor of～20-30 (in optical) over a period of ∼20 yr in the observed frame. This pronounced fading trend in brightness was first identified by comparing the magnitudes measured in the Subaru/Hyper Suprime-Cam (HSC) images with those in the Sloan Digital Sky Survey (SDSS) images for ～3×104quasars spectroscopically identified by SDSS. We performed follow-up observations, including optical imaging and spectroscopy as well as near-infrared imaging, with >4 m-class telescopes such as Subaru, GTC, Keck, and SOAR telescopes. We combine these new data with the archival data to examine the variability behavior over ∼20 yr in detail and even the longer-term trend of the variability over ∼70 yr in the observed frame. We find that (i) the active galactic nucleus (AGN) component likely faded by a factor of ∼50 from the early 2000s to 2023 and (ii) the observed brightness decline is best explained by a substantial decrease in accretion rate rather than time-varying line-of-sight dust obscuration. These findings are derived from multi-component (time-varying AGN + constant galaxy) spectral energy distribution fitting over multi-epochs, which is well consistent with the optical spectra. The Eddington ratio decreases by a factor of ∼50, from ∼0.4 to ∼0.008, if we use the black hole mass measured with the SDSS spectrum, which could be highly uncertain because of the very large variability. The total brightness is dominated by the host galaxy in the rest-frame optical wavelength rather than the AGN as of 2023.
