Green Bean galaxies and the fading echoes of AGN activity

TL;DR

This study investigates fading AGN activity in Green Bean galaxies by presenting spatially resolved optical spectroscopy of SDSS J095100.54+051026.7 using long-slit and scanning Fabry–Perot interferometry with the 6‑m SAO telescope. Through stellar population subtraction, emission-line fitting, and diagnostic diagrams (BPT and He II), it maps ionisation and kinematics out to ~40 kpc, finding LINER-like excitation in the nucleus and elevated ionisation in extended clouds. The results support a radiative fading scenario for the central AGN and demonstrate GP as a nearby laboratory for AGN duty cycles and radiative–kinetic transitions, with future work planned to combine optical data with radio observations.

Abstract

Green Bean is a rare type of galaxy which represents a short-lived phase in the life cycle of active galactic nuclei (AGN), characterised by large-scale, powerful ionised clouds in the circumgalactic medium. Recent studies demonstrate that these extended ionised structures may reflect fading signatures of past AGN activity, often manifested in the form of large-scale ionisation cones. The analysis of their observational properties provides unique constraints on AGN lifetimes, feedback mechanisms, and transitions between radiative and kinetic modes of activity. In this paper we announce the first results of the project dedicated to the long-slit spectroscopic and scanning Fabry-Perot interferometric observations of Green Bean galaxies at the Russian 6-m telescope with SCORPIO-2 multi-mode instrument. We describe the data reduction and spectral fitting procedures that allow one to characterise ionisation conditions in extended gaseous regions of the galaxy SDSSJ095100.54+051026.7.

Figures (2)

• Figure 1: (Top left:) Optical image from the DESI Legacy Survey. The white line indicates the position of the LS at PA = 72°, used for the spectroscopic observations. (Top right:) Line-of-sight velocity distribution derived from the long-slit spectroscopic data. Velocity distribution corrected for the systemic velocity $v_{sys}=71567\, km\,s^{-1}$. The green symbols represent the stellar-population-subtracted gas component in the central galactic region, while the red and blue symbols trace the velocity and its measurement errors in the extended clouds on either side of the galaxy. (Bottom:) Maps obtained from Voigt fitting of FPI spectra: flux map in the [O iii]$\lambda$5007 emission line (left) and corresponding line-of-sight velocity field (right).
• Figure 2: (Top): Nuclear spectrum of GP. The observed SCORPIO-2 spectrum is shown in light gray, the stellar population model — in orange. The dark gray line corresponds to the residual spectrum after subtracting the stellar continuum. The green dashed and red dashed lines represent Gaussian fits to the [O iii]+H$\beta$ and [N ii]+H$\alpha$ emission lines, respectively. Telluric absorption lines are marked with the $\oplus$ symbol at the corresponding wavelengths. (Bottom left): Standard [O iii]$\lambda$5007/H$\beta$ vs. [N ii]$\lambda$6583/H$\alpha$ (BPT) diagram. The solid and dashed curves represent the separation lines between different ionization sources Kewley2001Kauffmann2003Schawinski2007. (Bottom right): He ii/H$\beta$ vs. [N ii]$\lambda$6583/H$\alpha$ diagram Shirazi2012. The green point marks the central galactic region, while the red and blue points show the integrated line ratios for the extended clouds.