The complete local volume groups sample – III. Characteristics of group central radio galaxies in the Local Universe

Abstract

Using new 610 MHz and 235 MHz observations from the Giant Metrewave Radio Telescope (GMRT) in combination with archival GMRT and Very Large Array (VLA) survey data we present the radio properties of the dominant early-type galaxies in the low-richness sub-sample of the Complete Local-volume Groups Sample (CLoGS; 27 galaxy groups) and provide results for the radio properties of the full CLoGS sample for the first time. We find a high radio detection rate in the dominant galaxies of the low-richness sub-sample of 82% (22/27); for the full CLoGS sample the detection rate is 87% (46/53). The group-dominant galaxies exhibit a wide range of radio power, 10 20 − 10 25 W Hz −1 in the 235 and 610 MHz bands, with the majority (53%) presenting point-like radio emission, 19% hosting currently active radio jets, 6% having remnant jets, 9% being diffuse and 13% having no detected radio emission. The mean spectral index of the detected radio sources in the 235−610 MHz frequency range is found to be α 610 235 ∼0.68, and α 1400 235 ∼0.59 in the 235−1400 MHz one. In agreement with earlier studies, we find that the fraction of ultra-steep spectrum sources (α >1.3) is ∼4%, mostly dependent on the detection limit at 235 MHz. The majority of pointlike systems are found to reside in dynamically young groups, whereas jet systems show no preference between spiral-rich and spiral-poor group environments. The mechanical power of the jet sources in the low-richness sample groups is estimated to be ∼10 42 − 10 44 erg s −1 with their black hole masses ranging between 2×10 8 − 5×10 9 M . We confirm previous findings that, while radio jet sources tend to be associated with more massive black holes, black hole mass is not the decisive factor in determining jet activity or power.

Feedback from Active Galactic Nuclei in Galaxy Groups

“…Radio surveys have made clear that the centers of galaxy groups and clusters are special locations for AGN (e.g., [89,187,188]), with group-central galaxies twice as likely to host radio-mode activity than non-central galaxies of equal mass out to z > 1. Deeper observations show that almost all the central galaxies of X-ray luminous groups host some radio emission [189,190], though in the local universe some of these may be contaminated by emission from low-level star formation [191]. The observations of nearby groups show a wide range of radio morphologies (e.g., [192]), with jet-mode feedback dominated by FR-I radio galaxies, as in clusters.…”

“…The observations of nearby groups show a wide range of radio morphologies (e.g., [192]), with jet-mode feedback dominated by FR-I radio galaxies, as in clusters. Roughly one-third of X-ray luminous groups appear to host currently or recently active jet sources in their central galaxies [106] with typical jet powers in the range 10 41 -10 44 erg s −1 [190].…”

AGN feedback and galaxy evolution in nearby galaxy groups using CLoGS

“…Of the radio detected BGEs, 53% present point-like radio emission, followed by 19% having jets with non-detections at 13%. We find that radio morphology correlates with the dynamical youth of the groups as radio point sources are more common in the dominant galaxies of spiral-rich systems whereas jet sources show no preference of their close environment (Kolokythas et al 2018(Kolokythas et al , 2019.…”

The eROSITA Final Equatorial-Depth Survey (eFEDS)

“…They also argued that radio galaxies showing jets are more common in bright groups, while radio non-detections are mostly found in X-ray faint systems. The same authors report, in the CLoGS low-richness sample (27 objects) studied in Kolokythas et al (2019), a radio detection rate of ∼82% in the luminosity range 10 20 − 10 25 W Hz −1 at 235 MHz. Malarecki et al (2015) proposed that the lower densities in the IGrM, compared to the ICM, allows the lobes of group radio galaxies to expand to large distances.…”

“…As already discussed in Sec. 1, Kolokythas et al (2018Kolokythas et al ( , 2019) report rates at 235 MHz of 92% and 82% for their sample of 26 and 27 galaxy groups, respectively. P20 report a detection rate for COSMOS groups of ∼70%, with rms ∼ 12µJy beam −1 .…”