The luminosity history of fading local quasars over 10$^{4-5}$ years as observed by VLT/MUSE

TL;DR

This study reconstructs the luminosity history of five nearby fading quasars over 40,000 to 80,000 years using VLT/MUSE observations, revealing significant fluctuations in AGN activity consistent with theoretical models.

Contribution

It introduces a method to infer AGN luminosity changes over tens of thousands of years by analyzing extended emission-line regions with integral field spectroscopy.

Findings

All sources show a fading trend in AGN luminosity by 0.2-3 dex.

AGN activity fluctuates significantly over 10,000 to 100,000-year timescales.

Results support models of long-term AGN variability and feedback effects.

Abstract

We present a comprehensive study of five nearby active galaxies featuring large (tens of kpc) extended emission-line regions (EELRs). The study is based on large-format integral field spectroscopic observations conducted with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). The spatially resolved kinematics of the ionized gas and stellar components show signs of rotation, bi-conical outflows, and complex behavior likely associated with past interactions. Analysis of the physical conditions of the EELRs indicates that in these systems, the active galactic nucleus (AGN) is the primary ionization source. Using radiative transfer simulations, we compare the ionization state across the EELRs to estimate the required AGN bolometric luminosities at different radial distances. Then, considering the projected light travel time, we reconstruct the inferred AGN luminosity curves. We find that all sources are consistent with a fading trend in intrinsic AGN luminosity by 0.2--3 dex over timescales of 40,000--80,000 years, with a time dependence consistent with previous studies of fading AGNs. These results support the hypothesis that most AGN undergo significant fluctuations in their accretion rates over multiple timescales ranging from 10,000 to 1,000,000 years, as proposed by existing theoretical models. These results provide new insights into the transient phases of AGN activity at previously unexplored scales and their potential long-term impact on their host galaxies through various feedback mechanisms.