The relation between the diffuse X-ray luminosity and the radio power of the central AGN in galaxy groups

Abstract

Our understanding of how AGN feedback operates in galaxy clusters has improved in recent years owing to large efforts in multi-wavelength observations and hydrodynamical simulations. However, it is much less clear how feedback operates in galaxy groups, which have shallower gravitational potentials. In this work, using very deep VLA and new MeerKAT observations from the MIGHTEE survey, we compiled a sample of 247 X-ray selected galaxy groups detected in the COSMOS field. We have studied the relation between the X-ray emission of the intra-group medium and the 1.4 GHz radio emission of the central radio galaxy. For comparison, we have also built a control sample of 142 galaxy clusters using ROSAT and NVSS data. We find that clusters and groups follow the same correlation between X-ray and radio emission. Large radio galaxies hosted in the centres of groups and merging clusters increase the scatter of the distribution. Using statistical tests and Monte-Carlo simulations, we show that the correlation is not dominated by biases or selection effects. We also find that galaxy groups are more likely than clusters to host large radio galaxies, perhaps owing to the lower ambient gas density or a more efficient accretion mode. In these groups, radiative cooling of the ICM could be less suppressed by AGN heating. We conclude that the feedback processes that operate in galaxy clusters are also effective in groups.

Feedback from Active Galactic Nuclei in Galaxy Groups

“…The properties of group-central radio galaxies are closely linked to the IGrM. Both groups and clusters show a correlation between X-ray luminosity and the radio luminosity of the central source [189,196,197]. In clusters, central radio source luminosity is observed to be higher in systems with cooling times <10 9 yr [198] and, in groups, it appears that radio jets are more common in the central galaxies of groups with short central cooling times, low t cool /t ff ratios, and declining central temperature profiles [106].…”

“…However, the population of group-central radio galaxies includes much larger objects, some of which extend to very large radii, well beyond the cool core, and even into the outskirts of their groups. Pasini et al [197] show that radio galaxies larger than 200 kpc are more common in groups than clusters, and the largest radio galaxies are located in groups, probably because the IGrM is less able to confine their growth than the ICM. There is also evidence from new radio surveys, with greater sensitivity to extended diffuse emission, that giant radio galaxies may be more common, in general, than previously believed [201].…”

“…While its spatial resolution is modest (∼100 ), its high sensitivity at low frequency and provision of fluxes in multiple bands makes it a powerful tool for studying radio galaxies, particularly old, fading sources. Higher frequency (∼1 GHz), higher spatial resolution (8-30 ) surveys of continuum emission and HI are becoming available from ASKAP (e.g., RACS, WALLABY, [357,358]) and MeerKAT (e.g., MIGHTEE, [359]), and these observatories are beginning to produce interesting findings on, e.g., group dynamics and evolution [360,361] and the population of giant radio galaxies [197,201].…”

The eROSITA Final Equatorial-Depth Survey (eFEDS)

“…Because of the large number of upper limits, we relied on statistical tests, such as the partial correlation Kendall's τ test and the scrambling test, to show that the correlation is not produced by selection effects in the radio band. -Converting the 144 MHz power of radio galaxies to 1.4 GHz, we compared our results with the correlation between the Xray luminosity and the 1.4 GHz power of a COSMOS galaxy groups sample first investigated by Pasini et al (2020). We found that the two samples are in good agreement based on a Kolmogorov-Smirnov test that, under the null-hypothesis that the samples are drawn from the same parent distribution, gives p = 0.41.…”

“…To ascertain if the correlation is genuinely detected, we performed the partial correlation Kendall's τ (Akritas & Siebert 1996) test. This tool has already been used in a number of papers (e.g., Ineson et al 2015;Pasini et al 2020) to test correlations in the presence of upper limits and redshift-dependence. The algorithm estimates the null-hypothesis probability that selection effects are producing the correlation.…”