The prevalence of radio-loud active galactic nucleus (AGN) activity in present-day massive haloes is determined using a sample of 625 nearby groups and clusters selected from the Sloan Digital Sky Survey. Brightest group and cluster galaxies (BCGs) are more likely to host a radio-loud AGN than other galaxies of the same stellar mass (by below a factor of 2 at a stellar mass of ∼5 × 10¹¹ M_⊙, but rising to over an order of magnitude below 10¹¹ M_⊙). The distribution of radio luminosities for BCGs does not depend on mass, however, and is similar to that of field galaxies of the same stellar mass. Neither the radio-loud fraction nor the radio luminosity distribution of BCGs depends strongly on the velocity dispersion of the host cluster. The radio-AGN fraction is also studied as a function of distance from the cluster centre. Only within 0.2r₂₀₀ do cluster galaxies exhibit an enhanced likelihood of radio-loud AGN activity, which approaches that of the BCGs. In contrast to the radio properties, the fraction of galaxies with optical emission-line AGN activity is suppressed within r₂₀₀ in groups and clusters, decreasing monotonically towards the cluster centre.

A sample of 2712 radio-luminous galaxies is defined from the second data release of the Sloan Digital Sky Survey (SDSS) by cross-comparing the main sp

A long-standing problem for models of galaxy formation has been the mismatch between the predicted shape of the mass function of dark matter halos and the observed shape of the luminosity function of galaxies. The number of massive haloes is predicted to decrease as a power law (N∝M−2) out to very large masses, while the galaxy luminosity function cuts off exponentially at luminosities above L*. This implies that the efficiency with which gas cools onto massive systems is lower than expected. This letter investigates the role of radio-loud active galactic nuclei (AGN) in continually re-heating the cooling gas. By combining two observational results, the time-averaged energy output associated with recurrent radio source activity is determined, as a function of the black hole mass of the host galaxy: . It is shown that for massive elliptical galaxies this radio-source heating balances the radiative energy losses from the hot gas surrounding the galaxy. The recurrent radio-loud AGN activity may therefore provide a self-regulating feedback mechanism capable of controlling the rate of growth of galaxies.

Source classifications, stellar masses and star formation rates are presented for ≈80,000 radio sources from the first data release of the Low Frequency Array Two-metre Sky Survey (LoTSS) Deep Fields, which represents the widest deep radio survey ever undertaken. Using deep multi-wavelength data spanning from the ultraviolet to the far-infrared, spectral energy distribution (SED) fitting is carried out for all of the LoTSS-Deep host galaxies using four different SED codes, two of which include modelling of the contributions from an active galactic nucleus (AGN). Comparing the results of the four codes, galaxies that host a radiative AGN are identified, and an optimised consensus estimate of the stellar mass and star-formation rate for each galaxy is derived. Those galaxies with an excess of radio emission over that expected from star formation are then identified, and the LoTSS-Deep sources are divided into four classes: star-forming galaxies, radio-quiet AGN, and radio-loud high-excitation and low-excitation AGN. Ninety-five per cent of the sources can be reliably classified, more than two-thirds of which are star-forming galaxies, ranging from normal galaxies in the nearby Universe to highly-starbursting systems at z > 4. Star-forming galaxies become the dominant population below 150-MHz flux densities of ≈1 mJy, accounting for 90 per cent of sources at S_150MHz ∼ 100μJy. Radio-quiet AGN comprise ≈10 per cent of the overall population. Results are compared against the predictions of the SKADS and T-RECS radio sky simulations, and improvements to the simulations are suggested.

Hubble Space Telescope observations are presented of eight 3CR radio galaxies in the redshift interval l≾z≾1.3. The optical morphologies of these galaxies change dramatically as the radio size increases. It is shown that this evolution is entirely consistent with large-scale star formation induced by the radio jet, and it is argued that this mechanism could be the predominant cause of the observed alignment of the optical emission along the radio axis.