Extreme line profile variations in the repeating changing-look active galactic nucleus IRAS23226-3843

TL;DR

IRAS 23226-3843 is analyzed as a repeating changing-look AGN with extreme Balmer decrements and evolving broad-line profiles. The authors combine five years of Swift multiwavelength monitoring, dense ASAS-SN photometry, and new 2023–2024 optical spectra with archival data to trace continuum and BLR variability from 2007 to 2025. They identify a dramatic 2019 outburst followed by a sustained high state, with Balmer decrements around 10 and broad-line widths near 11,000 km s^-1, while line profiles shift from blue-asymmetric to double-peaked to symmetric, largely decoupled from continuum. The inferred low Eddington ratio and accretion-rate-driven variability, along with dynamic BLR geometry, position IRAS 23226-3843 as a key laboratory for studying recurrent changing-look phenomena in AGNs.

Abstract

IRAS23226-3843 has been identified as a highly variable Seyfert galaxy and even as a changing-look active galactic nucleus based on optical spectra. Here we present follow-up observations - taken over the past five years - for examining the ongoing photometric and spectral variations in this remarkable galaxy. We carried out SWIFT observations of IRAS23226-3843 together with new optical spectra taken in 2023 and 2024. In parallel we investigate ASAS-SN photometric data from 2014 till 2025. IRAS23226-3843 stayed on a high continuum flux level in the X-ray as well as in the optical since a historic outburst in 2019. However, it shows strong short-term variations on timescales of a few months. Densely sampled ASAS-SN V-band continuum data from 2014 till 2025 confirm that behavior. IRAS23226-3843 switched from a clear Seyfert 1 type in December 2019 to a Seyfert 1.9/2 type in July 2020 based on its optical spectra. Afterward, it again became a Seyfert 1 type with symmetric broad single-peaked Balmer line profiles in January 2023. These spectra prove the repeating changing-look character of the galaxy.IRAS23226-3843 exhibits extreme high Balmer decrements Ha\Hb based on their broad line components. The Balmer decrement values are on the order of 10. IRAS23226-3843 successively showed all types of broad line Balmer profiles during the past 25 years over periods of many years: asymmetric single-peaked, double-peaked, as well as single-peaked and symmetric profiles in addition to its Seyfert 1.9/2 transition. These variations are not clearly correlated with continuum and line intensity variations.

Figures (8)

• Figure 1: Integrated Swift image (25 ksec) in the UVOT-W2 band of IRAS 23226-3843. North is to the top, east to the left. 20 arcsec correspond to 13.7 kpc at the distance of IRAS 23226-3843.
• Figure 2: DESI legacy image (g,r,i,z-band) of IRAS 23226-3843. North is to the top, east to the left. This image shows the section from Fig. \ref{['Im_SWIFT_iras_23226_w2']}.
• Figure 3: Combined X-ray, UV, and optical light curves taken with the Swift satellite for the years 2007 until 2025. The fluxes are given in units of 10$^{-12}$ ergs s$^{-1}$ cm$^{-2}$. $\Gamma$ is the X-ray photon index.
• Figure 4: Optical light curve of IRAS 23226-3843 based on ASAS-SN data for the years 2014 to 2025. In addition we show the Swift V-band fluxes (red crosses) as well as the continuum fluxes at 5050 Å based on our optical spectra (orange crosses).
• Figure 5: Optical spectra of IRAS 23226-3843 for the years 1997 until 2024. The decreasing spectra from 1997 until 2017 are shown in cyan. The spectra taken during the outburst in 2019 are shown in black. The latest spectra are shown in red (2020), blue (2023), and green (2024).