The clustering of radio galaxies atz≃ 0.55 from the 2SLAQ LRG survey

Abstract

We examine the clustering properties of low-power radio galaxies at redshift 0.4 < z < 0.8, using data from the 2SLAQ Luminous Red Galaxy (LRG) survey, and find that radio-detected LRGs (with typical optical luminosities of 3-5L * and 1.4 GHz radio powers in the range 10 24 -10 26 W Hz −1 ) are significantly more clustered than a matched population of radio-quiet ( 10 24 W Hz −1 ) LRGs with the same distribution in optical luminosity and colour.The measured scalelength of the two-point cross-correlation function between the full LRG sample and the radio-detected LRGs is 9.57 ± 0.50 h −1 Mpc, compared to 8.47 ± 0.27 h −1 Mpc for the matched sample of radio-quiet LRGs; while the implied scalelength of the auto-correlation function, r 0 , is 12.3 ± 1.2 h −1 Mpc and 9.02 ± 0.52 h −1 Mpc for the radio-detected and radio-quiet samples, respectively. We further interpret our clustering measurements in the halo model framework and demonstrate that the radio-detected LRGs have typical halo masses of 10.1 ± 1.4 × 10 13 h −1 M and bias of 2.96 ± 0.17, compared to 6.44 ± 0.32 × 10 13 h −1 M and 2.49 ± 0.02 for the radio-quiet sample. A model in which the radio-detected LRGs are almost all central galaxies within haloes provides the best fit to the measured clustering, and we estimate that at least 30 per cent of all 2SLAQ LRGs with the same clustering amplitude as the radio-detected LRGs are currently radio loud.Our results imply that radio-detected galaxies in the 2SLAQ LRG sample typically occupy more massive haloes than other LRGS of the same optical luminosity, so the probability of finding a radio-loud active galactic nucleus (AGN) in a massive galaxy at z ∼ 0.55 is influenced by the halo mass and/or cluster environment in addition to the well-known dependence on optical luminosity. If we model the radio-detected fraction of LRGs, F rad , as a function of halo mass M, then the data are well-fitted by a power law of the form F rad ∝ M 0.65±0.23 . The observed relationship between radio emission and clustering strength could plausibly arise either through a higher fuelling rate of gas on to the central black holes of galaxies in the most massive haloes (producing more powerful radio jets) or through the presence of a denser IGM (which would provide a more efficient working surface for the jets, thus boosting their observed radio luminosity). Further work is needed to determine which of these effects is dominant.

Galaxy And Mass Assembly (GAMA): the environments of high- and low-excitation radio galaxies

“…Wake et al 2008;Mandelbaum et al 2009;Donoso et al 2010) have shown that radio-loud LRGs (analogous to LERGs) are in more massive haloes than non-radio galaxies of similar stellar mass, which is in agreement with our results on Σ5 and group fraction. Also in agreement with our work, Gendre et al (2013) use a sample of z < 0.3 radio galaxies to show that LERGs have denser average environments than HERGs, although there is no direct control for stellar mass in their work.…”

“…In contrast, the environments of the HERGs and lower luminosity LERGs are indistinguishable from that of a matched control sample. Our results imply that high-luminosity LERGs lie in more massive haloes than non-radio galaxies of similar stellar mass and colour, in agreement with earlier studies (Wake et al 2008;Donoso et al 2010). When we control for the preference of LERGs to be found in groups, both high-and low-luminosity LERGs are found in higher-mass haloes (∼ 0.2 dex; at least 97 percent significant) than the non-radio control sample.…”

“…Best 2004;Wake et al 2008;Mandelbaum et al 2009;Donoso et al 2010). We do not see this difference in halo mass for low-luminosity LERGs, except when we only compare those in groups, in which case, low-luminosity LERGs are also in higher mass haloes than their control sample.…”

Probing the radio loud/quiet AGN dichotomy with quasar clustering

“…In these samples, the typical 1.4 GHz radioluminosities for AGNs is 10 23 -10 26 W Hz −1 which is represen- Fig. 12: Different values for the real-space correlation length r 0 against redshift for RLQs and RQQs from SDSS DR5 (purple and gray downward triangles, Shen et al 2009), optical quasars (gray circles, Croom et al 2005;Ross et al 2009;Eftekharzadeh et al 2015), radio galaxies (dark green squares, Peacock & Nicholson 1991;Magliocchetti et al 2004;Wake et al 2008;Fine et al 2011;Lindsay et al 2014b), and FSRQs (orange star, Allevato et al 2014a) tative of FRI sources, whilst for our sample the average radioluminosity is ∼ 8 × 10 26 W Hz −1 , which is near the boundary between FRI and FRII sources.…”

Radio Continuum Surveys with Square Kilometre Array Pathfinders

“…Studies of galaxies in groups and clusters by Best et al (2007) and Wake et al (2008) have shown that the environment of a radio galaxy has a significant effect on the radio emission. Sabater et al (2008Sabater et al ( , 2012 built on this result by comparing (a) the radio AGN activity in a sample of isolated galaxies (AMIGA sample; Verdes-Montenegro et al 2005) with that of a matched sample of galaxies in clusters (Miller & Owen 2001;Reddy & Yun 2004) The dependence of the redshift of the peak in space density (z peak ) on radio power for the best-fitting steep spectrum grid, showing that the numbers of the most powerful radio sources peak at the highest redshifts (Rigby et al 2011).…”