Investigating AGN feedback in Hα-luminous galaxy clusters: First Chandra X-ray analysis of Abell 2009

¹ Scuola Universitaria Superiore IUSS Pavia, Palazzo del Broletto, Piazza della Vittoria 15, I-27100 Pavia, Italy
² Department of Physics, University of Trento, Via Sommarive 14, I-38123 Povo, (TN), Italy
³ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁴ Istituto Nazionale di Astrofisica (INAF) – Istituto di Radioastronomia (IRA), Via Gobetti 101, I-40129 Bologna, Italy

^⋆ Corresponding author; ilaria.fornasiero@iusspavia.it

Received: 5 December 2024
Accepted: 22 February 2025

Abstract

Aims. We analyze the X-ray and radio properties of the galaxy cluster Abell 2009 (z ∼ 0.152) to complete the in-depth individual study of a subsample of objects from the ROSAT Brightest Cluster Sample (BCS) with a relatively high X-ray flux and Hα line luminosity, which is a promising diagnostic of the presence of cool gas in the cluster cores. Our aim is to investigate the feedback from the active galactic nucleus (AGN) in the central galaxy and the intracluster medium (ICM) of relaxed clusters.

Methods. In this work, we analyze archival data from JVLA and Chandra observations. We performed a morphological analysis of both the X-ray emission from the ICM of Abell 2009 and of the radio emission from the AGN in the central galaxy. We also performed a spectral analysis of the X-ray emission, to derive the global properties and radial profiles of the thermal gas.

Results. Our X-ray analysis confirms the expectations, based on the selection criteria, that Abell 2009 is a cool-core system. We estimate a cooling radius of ∼88 kpc within which the ICM is radiating away its energy at rates of L_cool ∼ 4.4 × 10⁴⁴ erg s⁻¹. Radio observations of the central galaxy reveal a bright core surrounded by radio lobes on 30 kpc scales, with a symmetric butterfly-shaped morphology. We also present the detection of an extended radio galaxy to the northwest of the central one that is also a cluster member of Abell 2009. Although we did not detect any clear X-ray cavity at the position of the central radio lobes by assuming that their size is comparable, we combined the volume of the lobes with the pressure of the surrounding ICM to derive the work done by the AGN on the gas to inflate them. By estimating a cavity age of about 20 Myr, this corresponds to a mechanical power of ≈10⁴⁵ erg s⁻¹, which is sufficient to counterbalance the radiative cooling losses in Abell 2009. We finally discuss possible correlations between the global properties of the 18 objects from the BCS selection, finding in particular that the number of outbursts required to counterbalance the radiative ICM losses is linearly anticorrelated with the energetics and power of the outburst.