Evolution in the clustering strength of radio galaxies

Abstract

We cross match the NVSS and FIRST surveys with three large photometric catalogues of luminous red galaxies (LRGs) to define radio-loud samples. These have median redshifts 0.35, 0.55 and 0.68 and, by matching rest-frame optical and radio properties, we construct uniform samples across the three surveys. This paper is concerned with the clustering properties of these samples derived from the angular correlation function. The primary aim is to characterise any evolution in the clustering amplitude of radio galaxies bellow z~0.68. We find no evidence for evolution in the large-scale (~1-50h^{-1}Mpc) clustering amplitude. Our radio galaxy autocorrelations are consistent with previous findings indicating little-to-no evolution in the redshift range 0.68 to 0 (~6Gyr of time). We also cross correlate radio galaxies with the parent LRG samples to increase the precision of our results and again find no evidence for evolution. Our results are inconsistent with a long-lived model for the clustering evolution that assumes radio sources randomly sample the LRG population. A model where the halo mass is constant with redshift is consistent with the data. This is similar to QSOs that have clustering amplitudes consistent with a single halo mass at all redshifts. Given that the brightest radio sources show stronger evolution in space density compared to fainter radio sources we restrict our samples to include only objects with L>10^{26}W/Hz and repeat the analysis. Again we find no evidence for evolution in the comoving correlation amplitude. These radio sources appear to inhabit the same mass halos as fainter radio galaxies (~9x10^{13}h^{-1}M_\odot). These halos are ~twice as massive as those of the general LRG population and ~30 times as massive as optical AGN/QSOs.Comment: 9 pages, 8 figures, accepted MNRA

Probing the radio loud/quiet AGN dichotomy with quasar clustering

“…12, we show our r 0 measurements along with results from previous works for radio galaxies (Peacock & Nicholson 1991;Magliocchetti et al 2004;Wake et al 2008;Fine et al 2011;Lindsay et al 2014b;Allison et al 2015;Nusser & Tiwari 2015), optically-selected quasars Croom et al 2005;Eftekharzadeh et al 2015), and γ − selected blazars (Allevato et al 2014a). In these samples, the typical 1.4 GHz radioluminosities for AGNs is 10 23 -10 26 W Hz −1 which is represen- Fig.…”

“…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.…”

“…Clustering statistics offer an efficient way to explore the connections between AGN types, including radio, X-ray, and infrared selected AGNs (Hickox et al 2009); obscured and unobscured quasars (Hickox et al 2011;Allevato et al 2014b;DiPompeo et al 2015); radio galaxies (Magliocchetti et al 2002;Wake et al 2008;Fine et al 2011); blazars (Allevato et al 2014a); and AGNs and galaxy populations: Seyferts and normal galaxies; and optical quasars and submillimeter galaxies (Hickox et al 2012). These findings open up the possibility to explain the validity and simplicity of unification schemes (e.g.…”

What drives the growth of black holes?

“…The clustering of radio-quiet AGNs is weaker than radio-loud AGNs out to z ≈ 1-2, with implied darkmatter halo masses of ≈ 10 12 -10 13 M and ≈ (0.3-1.0) ×10 14 M , respectively (e.g., Li et al 2006;dâ Angela et al 2008;Coil et al 2009;Gilli et al 2009;Hickox et al 2009Hickox et al , 2011Mandelbaum et al 2009;Krumpe et al 2010;Fine et al 2011; however, also see Bradshaw et al 2011), with some evidence that the clustering strength is dependent on the adopted AGN luminosity thresholds (e.g., Krumpe et al, 2010); see Fig. 5.…”

Counting quasar–radio source pairs to derive the millijansky radio luminosity function and clustering strength toz = 3.5

“…We will use this empirical fit to estimate r 0QQ (z). The clustering of mJy radio sources has been extensively studied at redshifts below ∼0.8 with samples cross-matched to optical spectroscopic or photometric galaxies (Peacock & Nicholson 1991;Brand et al 2005;Wake et al 2008b;Donoso et al 2010;Fine et al 2011;Lindsay et al 2014a). At the radio luminosities sampled in those surveys (L 10 24 W Hz −1 ) the radio population is dominated by AGN typically hosted by LRGs.…”