Detections of inflowing gas from narrow absorption lines at parsec scales

¹ Department of physics, Guangxi University for Nationalities, Nanning 530006, PR China
e-mail: zhichenfu@126.com
² Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, PR China
e-mail: gumf@shao.ac.cn
³ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, PR China
e-mail: zcho@ustc.edu.cn
⁴ School of Astronomy and Space Science, Nanjing University, Nanjing 210093, PR China
⁵ Center for Astrophysics, Guangzhou University, Guangzhou 510006, PR China
⁶ School of Materials Science and Engineering, Baise University, Baise 533000, PR China

Received: 25 September 2021
Accepted: 13 December 2021

Abstract

The detection of inflows at the scale of the dusty torus and smaller is crucial for investigating the process of supermassive black hole (SMBH) accretion. However, only a few cases of inflowing gas at small scales have been reported through redshifted broad absorption lines so far. Here we report nine redshifted narrow absorption lines (NALs) of Mg⁺ ions with inflowing speeds of 1071–1979 km s⁻¹, which are likely along the directions close to the axes of accretion disks. The quasars showing inflowing Mg II NALs have, on average, slightly smaller Eddington ratios than the sources with outflowing Mg II NALs. The upper limits on the locations of the detected NALs are at parsec scale, that is, the distance from dusty tori to their central SMBHs. One possible origin of these infalling NALs is from dusty tori. However, these infalling NALs could also be naturally explained by chaotic cold accretion resulting from the nonlinear interaction of active galactic nucleus (AGN) jets with the interstellar medium (ISM), and these cold gaseous blobs may originally precipitate in metal-rich trailing outflows uplifted by AGN jet ejecta. The infalling NALs may therefore provide direct evidence for cold gas precipitation and accretion in AGN feedback processes, and provide direct evidence of inflowing gas along the directions close to quasar jets and at parsec scale. Regardless of whether these infalling NALs are from the dusty tori or the interaction of AGN jets with the ISM, the infalling NALs cannot provide sufficient fuel to power the quasars.