Extreme AGN feedback in the fossil galaxy group SDSSTG 4436

¹ Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
² INAF – IASF Milano, Via Alfonso Corti 12, 20133 Milan, Italy
³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁴ School of Physics and Astronomy, University of Birmingham, Birmingham B152TT, UK
⁵ INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
⁶ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, P.O. Box 94 Makhanda 6140, South Africa
⁷ South African Radio Astronomy Observatory, Black River Park North, 2 Fir St, Cape Town 7925, South Africa
⁸ SRON Netherlands Institute for Space Research, Niels Bohrweg 4, NL-2333 CA Leiden, The Netherlands
⁹ Department of Physics and Astronomy, University of Alabama in Huntsville, Huntsville, AL 35899, USA
¹⁰ Argelander Institute für Astronomie, Auf dem Hügel 71, D-53121 Bonn, Germany
¹¹ Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹² Institute of Astronomy, University of Cambridge, Madingley Road Cambridge CB3 0HA, UK,
¹³ Kavli Institute for Cosmology (KICC), University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁴ Department of Astronomy, Tsinghua University, Beijing 100084, China
¹⁵ Departamento de Física Teórica, M-8, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
¹⁶ Centro de Investigación Avanzada en Física Fundamental, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
¹⁷ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy
¹⁸ Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2, 00560 Helsinki, Finland
¹⁹ Department of Computer Science, Aalto University, PO Box 15400 Espoo FI-00 076, Finland
²⁰ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Savitribai Phule Pune University Campus, Ganeshkhind, Pune 411007, India
²¹ NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
²² Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
²³ CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309, USA
²⁴ Tartu Observatory University of Tartu, Observatooriumi 1, 61602 Tõravere, Estonia
²⁵ Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia

^⋆ Corresponding author: Dominique.Eckert@unige.ch

Received: 18 April 2025
Accepted: 17 July 2025

Abstract

Supermassive black hole feedback is the currently favoured mechanism to regulate the star formation rate of galaxies and prevent the formation of ultra-massive galaxies (M_⋆ > 10¹² M_⊙). However, the mechanism through which the outflowing energy is transferred to the surrounding medium strongly varies from one galaxy evolution model to another, such that a unified model for active galactic nucleus (AGN) feedback does not currently exist. The hot atmospheres of galaxy groups are highly sensitive laboratories of the feedback process, as the injected black hole energy is comparable to the binding energy of halo gas particles. Here we report multi-wavelength observations of the fossil galaxy group SDSSTG 4436. The hot atmosphere of this system exhibits a highly relaxed morphology centred on the giant elliptical galaxy NGC 3298. The X-ray emission from the system features a compact core (< 10 kpc) and a steep increase in the entropy and cooling time of the gas, with the cooling time reaching the age of the Universe ∼15 kpc from the centre of the galaxy. The observed entropy profile implies a total injected energy of ∼1.5 × 10⁶¹ ergs, which given the high level of relaxation could not have been injected by a recent merging event. Star formation in the central galaxy NGC 3298 is strongly quenched and its stellar population is very old (∼10.6 Gyr). The currently detected radio jets have low power and are confined within the central compact core. All the available evidence implies that this system was affected by giant AGN outbursts that raised the entropy of the neighbouring gas to the point that the gas no longer efficiently cools. Our findings imply that AGN outbursts can be energetic enough to unbind gas particles and lead to the disruption of cool cores.