The detections of inflowing gas from narrow absorption lines at the parsec scale

TL;DR

This study reports the detection of nine redshifted narrow absorption lines indicating inflowing gas at parsec scales near supermassive black holes, providing insights into accretion processes and AGN feedback mechanisms.

Contribution

It presents the first systematic identification of inflowing narrow absorption lines at parsec scales, suggesting origins from dusty tori or chaotic cold accretion, and discusses their implications for black hole feeding.

Findings

Nine inflowing Mg II NALs detected at parsec scales.

Inflowing gas speeds range from 1071 to 1979 km/s.

Inflowing NALs are associated with slightly lower Eddington ratios.

Abstract

Inflows at the dusty torus and smaller scales is crucial to investigate the process of supermassive black hole accretion. However, only few cases of inflowing gas at small scales have been reported through redshifted broad absorption lines so far. Here we report 9 redshifted narrow absorption lines (NALs) of $\rm Mg^+$ ions with inflowing speeds of 1071 -- 1979 km/s, 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 when compared to the sources with outflow Mg II NALs. The upper limits of locations of the detected NALs are at parsec scale, around the distances of dusty tori to central SMBHs. The one possible origin of these infalling NALs is from dusty tori. Of course, these infalling NALs can also be naturally explained by chaotic cold accretion resulted from the nonlinear interaction of active galactic nucleus (AGN) jets with the interstellar medium, and these cold gaseous blobs may originally precipitate in metal-rich trailing outflows uplifted by AGN jet ejecta. The infalling NALs may thus provide direct evidence for cold gas precipitation and accretion in AGN feedback processes, and provide the direct evidence of inflowing gas along the directions close to quasar jets and at parsec scale. It does not matter whether these infalling NALs are from the dusty tori or the interaction of AGN jets with the ISM, the infalling NALs cannot provide sufficient fuels to power the quasars.