Extreme line profile variations in the repeating changing-look active galactic nucleus IRAS 23226-3843

¹ Institut für Astrophysik und Geophysik, Universität Göttingen Friedrich-Hund-Platz 1 37077 Göttingen, Germany
² Department of Physics, Geology, and Engineering Technology, Northern Kentucky University Highland Heights KY 41076, USA
³ Department of Physics, University of Johannesburg PO Box 524 2006 Auckland Park Johannesburg, South Africa
⁴ ESA, European Space Astronomy Centre (ESAC) 28692 Villanueva de la Cañada Madrid, Spain
⁵ Max-Planck-Insitut für Radioastronomie Auf dem Hügel 69 D-53121 Bonn, Germany
⁶ South African Astronomical Observatory, Observatory Road Observatory 7925 Cape Town, RSA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 13 November 2025
Accepted: 18 January 2026

Abstract

Aims. IRAS 23226-3843 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.

Methods. We carried out Swift observations of IRAS 23226-3843 together with new optical spectra taken in 2023 and 2024. In parallel we investigate ASAS-SN photometric data from 2014 till 2025.

Results. IRAS 23226-3843 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. IRAS 23226-3843 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. IRAS 23226-3843 exhibits extreme high Balmer decrements Hα/Hβ based on their broad line components. The Balmer decrement values are on the order of 10. IRAS 23226-3843 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.