The clustering and bias of radio-selected AGN and star-forming galaxies in the COSMOS field

Abstract

Dark matter haloes in which galaxies reside are likely to have a significant\nimpact on their evolution. We investigate the link between dark matter haloes\nand their constituent galaxies by measuring the angular two-point correlation\nfunction of radio sources, using recently released 3 GHz imaging over $\\sim 2 \\\n\\mathrm{deg}^2$ of the COSMOS field. We split the radio source population into\nStar Forming Galaxies (SFGs) and Active Galactic Nuclei (AGN), and further\nseparate the AGN into radiatively efficient and inefficient accreters.\nRestricting our analysis to $z<1$, we find SFGs have a bias, $b = 1.5\n^{+0.1}_{-0.2}$, at a median redshift of $z=0.62$. On the other hand, AGN are\nsignificantly more strongly clustered with $b = 2.1\\pm 0.2$ at a median\nredshift of 0.7. This supports the idea that AGN are hosted by more massive\nhaloes than SFGs. We also find low-accretion rate AGN are more clustered ($b =\n2.9 \\pm 0.3$) than high-accretion rate AGN ($b = 1.8^{+0.4}_{-0.5}$) at the\nsame redshift ($z \\sim 0.7$), suggesting that low-accretion rate AGN reside in\nhigher mass haloes. This supports previous evidence that the relatively hot gas\nthat inhabits the most massive haloes is unable to be easily accreted by the\ncentral AGN, causing them to be inefficient. We also find evidence that\nlow-accretion rate AGN appear to reside in halo masses of $M_{h} \\sim 3-4\n\\times 10^{13}h^{-1}$M$_{\\odot}$ at all redshifts. On the other hand, the\nefficient accreters reside in haloes of $M_{h} \\sim 1-2 \\times\n10^{13}h^{-1}$M$_{\\odot}$ at low redshift but can reside in relatively lower\nmass haloes at higher redshifts. This could be due to the increased prevalence\nof cold gas in lower mass haloes at $z \\ge 1$ compared to $z<1$.\n