The life of central radio galaxies in clusters: AGN-ICM studies of eRASS1 clusters in the ASKAP fields

TL;DR

This study investigates whether central AGN feedback from BCGs can balance ICM cooling in galaxy clusters by correlating ASKAP radio properties with eRASS1 X-ray properties across three ASKAP fields. Using 151 clusters (134 BCG radio detections) and robust cross-matching, the authors quantify radio power, largest linear size, and BCG–X-ray offsets, and relate them to cluster X-ray luminosity and cooling properties, including a cooling-radius luminosity $L_{X,r<R_ ext{cool}}$. They find a weak but significant $L_R$–$L_X$ relation and a CC-subsample shows a positive but highly scattered $L_ ext{mech}$–$L_{X,r<R_ ext{cool}}$ correlation, implying AGN feedback is not fully sufficient to offset cooling in high-mass clusters (typical efficiency around 13–22\% at $L_{X,r<R_ ext{cool}}\sim5.5\times10^{43}$ erg s$^{-1}$). Bootstrap and flux–flux analyses support the robustness of these trends but reveal substantial intrinsic scatter and sensitivity to outliers, underscoring the need for deeper, more complete multiwavelength data (eRASS5, broader radio catalogs) to refine the heating–cooling balance in cluster cores.

Abstract

The mechanical feedback from the central AGNs can be crucial for balancing the radiative cooling of the intracluster medium at the cluster centre. We aim to understand the relationship between the power of AGN feedback and the cooling of gas in the centres of galaxy clusters by correlating the radio properties of the brightest cluster galaxies (BCGs) with the X-ray properties of their host clusters. We used catalogues from the first SRG/eROSITA All-Sky Survey (eRASS1) along with ASKAP radio data. In total, we identified 134 radio sources associated with BCGs of the 151 eRASS1 clusters located in the PS1, PS2, and SWAG-X ASKAP fields. Non-detections were treated as upper limits. We correlated BCG radio luminosity, largest linear size (LLS), and BCG offset with the integrated X-ray luminosity of their host clusters. To characterise cool cores (CCs) and non-cool cores (NCCs), we used the concentration parameter $c_{R_{500}}$ and combined it with the BCG offset to assess cluster dynamical state. We analysed the correlation between radio mechanical power and X-ray luminosity within the CC subsample. We observe a potential positive trend between LLS and BCG offset, suggesting an environmental effect on radio-source morphology. We find a weak trend where more luminous central radio galaxies are found in clusters with higher X-ray luminosity. Within the CC subsample, there is a positive but highly scattered relationship between the mechanical luminosity of AGN jets and the X-ray cooling luminosity. This finding is supported by bootstrap resampling and flux-flux analyses. The correlation indicates that AGN feedback is ineffective in high-luminosity (high-mass) clusters. At a cooling luminosity of $L_{\mathrm{X},~r<R_\mathrm{cool}}\approx 5.50\times10^{43}$ erg/s, on average, AGN feedback appears to contribute only about 13%-22% of the energy needed to offset the radiative losses in the ICM.

Figures (13)

• Figure 1: Spatial distribution of the eRASS1 clusters with $\mathcal{L}_\mathrm{EXT}$$\ge 6$ is shown for the PS1 (top left), PS2 (right), and SWAG-X (bottom left) ASKAP fields. The data points are colour-coded according to their redshift, and their sizes are equal to their $R_{500}$ in arcminutes (see the $10\,\mathrm{arcmin}$ blue circle at the bottom right corner of each plot for a scale).
• Figure 2: X-ray and radio luminosities of the eRASS1/ASKAP cluster sample. In each plot, PS1, PS2, and SWAG-X subsamples are shown by red circles, green triangles, and blue squared, respectively. Left: Integrated X-ray luminosity in the $0.2-2.3\,\mathrm{keV}$ band within 300 kpc as a function of redshift. Right: Radio luminosity at 944 MHz against redshift. The downward arrows represent the upper limits. The solid/dotted/dashed lines in red/blue/green mark the flux limits in the PS1/SWAG-X/PS2 ASKAP fields.
• Figure 3: Central radio luminosity at 944 MHz versus largest linear size ($P-D$ diagram). The gray diamonds are the group and cluster central radio sources in the eFEDS field measured by LOFAR at 144 MHz Pasini_2022. The rescaling to 944 MHz luminosity is done by adopting $\alpha=1.0$.
• Figure 4: Physical separation of the BCGs from the X-ray centres in units of kpc. Left: Radio luminosity of the BCGs at 944 MHz versus BCG offsets. Right: Largest linear size of the BCGs versus BCG offsets. In both plots, the data points are colour-coded by redshift $z$, and the arrows indicate upper limits.
• Figure 5: Concentration parameter of the eRASS1/ASKAP clusters. Left: Concentration parameter ($c_{R_{500}}$) against the 944 MHz radio luminosity ($L_\mathrm{R}$). Right: Concentration parameter as a function of BCG offset. The green dashed horizontal line in each plot indicates the median $c_{R_{500}}$ value of the sample.