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

Abstract

Understanding the relationship between galaxies hosting active galactic nuclei (AGN) and the dark matter halos in which they reside is key to constraining how black-hole fueling is triggered and regulated. Previous efforts have relied on simple halo mass estimates inferred from clustering, weak gravitational lensing, or halo occupation distribution modeling. 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 halos with M 200b ∼ 10 12.5 M ⊙ . The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization-the fraction of halos with AGN in our sample is a few percent. 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 halos, our results suggest that the environmental signature of distinct fueling modes for luminous QSOs compared to moderate luminosity X-ray AGN is less obvious than previously claimed.

Evolution of the luminosity-to-halo mass relation of LRGs from a combined analysis of SDSS-DR10+RCS2

“…Fig. 7 in Leauthaud et al 2015). At small scales one expects the baryonic mass of LRGs to contribute to the lensing signal.…”

Exploring the halo occupation of AGN using dark-matter cosmological simulations

“…It is shown that very different HOD models are consistent with the two-point correlation function measurements. This suggests that independent observations must supplement the two-point correlation function statistic to constrain the halo-mass distribution of AGN (Leauthaud et al 2015) and/or new modelling approaches need to be developed to aid the interpretation of the data. This paper presents a new semi-empirical model for the large-scale distribution of AGN, which can be used to compare against observational results, make realistic predictions for the clustering signal expected in future experiments and test observational selection effects and biases.…”

hybrid-lenstool: a self-consistent algorithm to model galaxy clusters with strong- and weak-lensing simultaneously

“…Moreover, lensing can give us hints on galaxy evolution (e.g. Natarajan et al 1998;Limousin et al 2007;Natarajan et al 2009;Leauthaud et al 2012Leauthaud et al , 2015Li et al 2016;Sifón et al 2015;Niemiec et al 2017), and on the distant Universe as lenses behave as cosmic telescopes and thus allow us to observe high-redshift galaxies (e.g. Atek et al 2015Atek et al , 2018Alavi et al 2016;Bouwens et al 2017;D'Aloisio, Natarajan & Shapiro 2014;Ishigaki et al 2018;Kawamata et al 2018), study highly magnified galaxies at intermediate redshifts (e.g.…”