The luminosity history of fading local quasars over 10^4 − 5 years as observed by VLT-MUSE

¹ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
² Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
³ Eureka Scientific, 2452 Delmer Street Suite 100, Oakland, CA 94602-3017, USA
⁴ Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
⁵ Department of Physics and Astronomy, University of Alabama, Box 870324 Tuscaloosa, AL 35487, USA
⁶ NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
⁷ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich, Switzerland
⁸ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
⁹ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁰ Departamento de Astronomía, Universidad de Concepción, Concepción, Chile
¹¹ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile

^⋆ Corresponding author.

Received: 28 September 2024
Accepted: 24 June 2025

Abstract

We present a comprehensive study of five nearby active galaxies featuring large (tens of kiloparsecs) 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. An 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 compared 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 reconstructed 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 to 80 000 years, with a time dependence consistent with previous studies of fading AGNs. These results support the hypothesis that most AGNs 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 on previously unexplored scales and their potential long-term impact on their host galaxies through various feedback mechanisms.