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The dark matter haloes of moderate luminosity X-ray AGN as determined from weak gravitational lensing and host stellar masses.

Leauthaud, A. and Benson, A.J. and Civano, F. and Coil, A.L. and Bundy, K. and Massey, R. and Schramm, M. and Schulze, A. and Capak, P. and Elvis, M. and Kulier, A. and Rhodes, J. (2015) 'The dark matter haloes of moderate luminosity X-ray AGN as determined from weak gravitational lensing and host stellar masses.', Monthly notices of the Royal Astronomical Society., 446 (2). pp. 1874-1888.


Understanding the relationship between galaxies hosting active galactic nuclei (AGN) and the dark matter haloes in which they reside is key to constraining how black hole fuelling is triggered and regulated. Previous efforts have relied on simple halo mass estimates inferred from clustering, weak gravitational lensing, or halo occupation distribution modelling. In practice, these approaches remain uncertain because AGN, no matter how they are identified, potentially live a wide range of halo masses with an occupation function whose general shape and normalization are poorly known. In this work, we show that better constraints can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to the fiducial stellar-to-halo mass relation (SHMR) derived for all galaxies, irrespective of nuclear activity. Our technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z < 1 from the COSMOS field, we report the first measurements of weak gravitational lensing from an X-ray-selected sample. Comparing this signal to predictions from the global SHMR, we find that, contrary to previous results, most X-ray AGN do not live in medium size groups – nearly half reside in relatively low mass haloes with M200b ∼ 1012.5 M⊙. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization – the fraction of haloes with AGN in our sample is a few per cent. The number of AGN satellite galaxies scales as a power law with host halo mass with a power-law index α = 1. By highlighting the relatively ‘normal’ way in which moderate luminosity X-ray AGN hosts occupy haloes, our results suggest that the environmental signature of distinct fuelling modes for luminous quasars compared to moderate luminosity X-ray AGN is less obvious than previously claimed.

Item Type:Article
Keywords:Galaxies: abundances, Galaxies: active, Galaxies: haloes, Galaxies: Seyfert, Galaxies: stellar content.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:No date available
Date deposited:10 December 2014
Date of first online publication:January 2015
Date first made open access:No date available

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