The AGN–galaxy–halo connection: the distribution of AGN host halo masses to z = 2.5

Abstract

It is widely reported, based on clustering measurements of observed active galactic nuclei (AGN) samples, that AGN reside in similar mass host dark matter halos across the bulk of cosmic time, with log $\mathcal {M}/\mathcal {M}_{\odot }\sim 12.5-13.0$ to z ∼ 2.5. We show that this is due in part to the AGN fraction in galaxies rising with increasing stellar mass, combined with AGN observational selection effects that exacerbate this trend. Here, we use AGN specific accretion rate distribution functions determined as a function of stellar mass and redshift for star-forming and quiescent galaxies separately, combined with the latest galaxy-halo connection models, to determine the parent and sub-halo mass distribution function of AGN to various observational limits. We find that while the median (sub-)halo mass of AGN, $\approx 10^{12}\mathcal {M}_{\odot }$, is fairly constant with luminosity, specific accretion rate, and redshift, the full halo mass distribution function is broad, spanning several orders of magnitude. We show that widely used methods to infer a typical dark matter halo mass based on an observed AGN clustering amplitude can result in biased, systematically high host halo masses. While the AGN satellite fraction rises with increasing parent halo mass, we find that the central galaxy is often not an AGN. Our results elucidate the physical causes for the apparent uniformity of AGN host halos across cosmic time and underscore the importance of accounting for AGN selection biases when interpreting observational AGN clustering results. We further show that AGN clustering is most easily interpreted in terms of the relative bias to galaxy samples, not from absolute bias measurements alone.

The environments of the radio galaxy population in SIMBA

“…This is our first main finding -while majority of radio galaxies are the central galaxies in their respective halos consistent with previous results, 20% of radio galaxies in S are in satellite galaxies. This fraction is consistent with recent observations suggesting a nontrivial minority of bright AGN are hosted by satellites (Alam et al 2021;Aird & Coil 2021).…”

AGN accretion and black hole growth across compact and extended galaxy evolution phases

“…The luminosities of such sources are likely to be severely underestimated using our methodology and thus their contribution will not be included in our measured AGN fractions. As discussed by Aird & Coil (2021), if it is assumed that the incidence of Compton-thick AGN simply traces the incidence of Compton-thin populations, with little dependence on 𝐿 X or 𝐿 X /M * (e.g. Buchner et al 2015;Ricci et al 2017) or host galaxy properties, then our AGN fractions and accretion rate probability distributions could be corrected simply by applying a scale factor ∼ 1.25−2.0 (allowing for remaining uncertainties in the Compton-thick fraction).…”

The role of scatter and satellites in shaping the large-scale clustering of X-ray AGN as a function of host galaxy stellar mass

“…We also add to the intrinsic scatter in the stellar mass -halo mass relation, a measurement error of 0. In the following, we also compare with the AGN semi-empirical model of Aird & Coil (2021), for which we apply an X-ray luminosity cut at 𝐿 X > 10 42 . Lastly, we compare our predictions with the clustering estimates of SDSS quasars at 𝑧 ∼ 1.4 measured by Richardson et al (2012), and for this test we impose a limit on luminosity of 𝐿 X > 10 44 erg s −1 and on Hydrogen column density of 𝑁 H < 10 22 cm −2 to select only optical, nominally Type I AGN (e.g., Ricci et al 2017).…”

“…Marconi et al 2004;Shankar et al 2004Shankar et al , 2013Aversa et al 2015) and/or semi-empirical mock catalogues tuned to reproduce stellar mass functions, AGN X-ray luminosity functions and/or AGN clustering properties (e.g. Georgakakis et al 2019;Aird & Coil 2021;Allevato et al 2021) Further constraints on the co-evolution scenario are indeed provided by studying the spatial clustering of AGN, especially X-ray selected (e.g. Coil et al 2009;Krumpe et al 2010;Allevato et al 2011;Krumpe et al 2012;Mountrichas & Georgakakis 2012;Mendez et al 2016;Powell et al 2018;Viitanen et al 2019;Allevato et al 2019;Powell et al 2020).…”

“…Other groups have, instead, built the correlation between black hole mass and host halo mass by passing the scaling relation with host galaxy stellar mass or velocity dispersion and the AGN duty cycle (e.g. Georgakakis et al 2019;Aird & Coil 2021). Besides not allowing for any quantitative assessment of the underlying fundamental black hole-galaxy scaling relations, limiting the efficacy of these models in shedding light on the processes controlling the co-evolution of BHs and their hosts, the latter approach is still not immune to degeneracies between e.g.…”