The clustering properties of radio-selected AGN and star-forming galaxies up to redshifts z ∼ 3

Abstract

We present the clustering properties of a complete sample of 968 radio sources detected at 1.4 GHz by the Very Large Array (VLA)-COSMOS survey with radio fluxes brighter than 0.15 mJy. 92 per cent have redshift determinations from the Laigle et al. catalogue. Based on their radio luminosity, these objects have been divided into 644 AGN and 247 star-forming galaxies. By fixing the slope of the autocorrelation function to γ = 2, we find r_0=11.7^{+1.0}_{-1.1} Mpc for the clustering length of the whole sample, while r_0=11.2^{+2.5}_{-3.3} Mpc and r_0=7.8^{+1.6}_{-2.1} Mpc (r_0=6.8^{+1.4}_{-1.8} Mpc for z ≤ 0.9) are, respectively, obtained for AGN and star-forming galaxies. These values correspond to minimum masses for dark matter haloes of M_min=10^{13.6^{+0.3}_{-0.6}} M<SUB>☉</SUB> for radio-selected AGN and M_min=10^{13.1^{+0.4}_{-1.6}} M<SUB>☉</SUB> for radio-emitting star-forming galaxies (M_min=10^{12.7^{+0.7}_{-2.2}} M<SUB>☉</SUB> for z ≤ 0.9). Comparisons with previous works imply an independence of the clustering properties of the AGN population with respect to both radio luminosity and redshift. We also investigate the relationship between dark and luminous matter in both populations. We obtain <M<SUB>*</SUB>>/M<SUB>halo</SUB> ≲ 10<SUP>- 2.7</SUP> for AGN, and <M<SUB>*</SUB>>/M<SUB>halo</SUB> ≲ 10<SUP>- 2.4</SUP> in the case of star-forming galaxies. Furthermore, if we restrict to z ≲ 0.9 star-forming galaxies, we derive <M<SUB>*</SUB>>/M<SUB>halo</SUB> ≲ 10<SUP>- 2.1</SUP>, result that clearly shows the cosmic process of stellar build-up as one moves towards the more local universe. Comparisons between the observed space density of radio-selected AGN and that of dark matter haloes show that about one in two haloes is associated with a black hole in its radio-active phase. This suggests that the radio-active phase is a recurrent phenomenon.