A unifying evolutionary framework for infrared-selected obscured and unobscured quasar host haloes

Abstract

Recent measurements of the dark matter halo masses of infrared-selected obscured quasars are in tension -some indicate that obscured quasars have higher halo mass compared to their unobscured counterparts, while others find no difference. The former result is inconsistent with the simplest models of quasar unification that rely solely on viewing angle, while the latter may support such models. Here, using empirical relationships between dark matter halo and supermassive black hole masses, we provide a simple evolutionary picture that naturally explains these findings and is motivated by more sophisticated merger-driven quasar fueling models. The model tracks the growth rate of haloes, with the black hole growing in spurts of quasar activity in order to "catch-up" with the M bh -M stellar -M halo relationship. The first part of the quasar phase is obscured and is followed by an unobscured phase. Depending on the luminosity limit of the sample, driven by observational selection effects, a difference in halo masses may or may not be significant. For high luminosity samples, the difference can be large (a few to 10 times higher masses in obscured quasars), while for lower luminosity samples the halo mass difference is very small, much smaller than current observational constraints. Such a simple model provides a qualitative explanation for the higher mass haloes of obscured quasars, as well as rough quantitative agreement with seemingly disparate results.

AGN Luminosity and Stellar Age: Two Missing Ingredients for AGN Unification as Seen with iPTF Supernovae

“…Recent works support the idea that the host galaxy has enough dust (Burtscher et al 2016) to cause obscuration of the broad-line region. DiPompeo et al (2017) estimate the fraction of IR-selected "obscured" AGNs that are obscured by dust outside the torus to be ∼25%, while Buchner & Bauer (2017) estimate that 40% of all AGNs have considerable host galaxy obscuration. But objects with large measured column densities > N 10 H 23.5 cm −2 cannot be explained by host galaxy obscuration and need heavy obscuration around the nucleus.…”

Physical Models for the Clustering of Obscured and Unobscured Quasars

“…Qualitatively, treating the effective obscuring covering fraction as a function of time in a quasar's evolution provides a simple explanation for the fact that obscured and unobscured quasars have different observed properties such as host dark matter halo mass. DiPompeo et al (2017b) quantitatively showed that this evolutionary sequence is able to recreate clustering measurements. The key piece to evolutionary models is understanding the timescales at which the host galaxy and the quasar/black hole evolve.…”

“…One commonly invoked picture of quasar evolution is that quasar activity is triggered by a dramatic event such as a merger or disk instability. The quasar then remains active in an obscured state until it rids itself of obscuring material via radiative and mechanical feedback to become unobscured (e.g., Sanders et al 1988;Di Matteo et al 2005;Hopkins et al 2008;Alexander & Hickox 2012;DiPompeo et al 2017b;Hickox & Alexander 2018). Qualitatively, treating the effective obscuring covering fraction as a function of time in a quasar's evolution provides a simple explanation for the fact that obscured and unobscured quasars have different observed properties such as host dark matter halo mass.…”

“…Many evolutionary models postulate that as dark matter halos grow, black hole growth lags behind (e.g., Alexander et al 2008;Woo et al 2008;Kormendy & Ho 2013;DiPompeo et al 2017b). As these black holes grow in mass, they transition from an obscured phase to an unobscured phase via radiatively-driven blowout (e.g., Hopkins et al 2006Hopkins et al , 2008.…”

“…As these black holes grow in mass, they transition from an obscured phase to an unobscured phase via radiatively-driven blowout (e.g., Hopkins et al 2006Hopkins et al , 2008. DiPompeo et al (2017b) presented a simple evolutionary model in which black hole growth lagged behind galaxy growth. In the DiPompeo et al (2017b) model, the host dark matter halo grows continuously, while the black hole grows in brief episodes.…”