The angular clustering of infrared-selected obscured and unobscured quasars

Abstract

Recent studies of luminous infrared-selected active galactic nuclei (AGN) suggest that the reddest, most obscured objects display a higher angular clustering amplitude, and thus reside in higher-mass dark matter halos. This is a direct contradiction to the prediction of the simplest unification-by-orientation models of AGN and quasars. However, clustering measurements depend strongly on the "mask" that removes low-quality data and describes the sky and selection function. We find that applying a robust, conservative mask to WISE-selected quasars yields a weaker but still significant difference in the bias between obscured and unobscured quasars. These findings are consistent with results from previous Spitzer surveys, and removes any scale dependence of the bias. For obscured quasars with z = 0.99 we measure a bias of b q = 2.67 ± 0.16, corresponding to a halo mass of log(M h /M ⊙ h −1 ) = 13.3 ± 0.1, while for unobscured sources with z = 1.04 we find b q = 2.04 ± 0.17 with a halo mass log(M h /M ⊙ h −1 ) = 12.8 ± 0.1. This improved measurement indicates that WISE-selected obscured quasars reside in halos only a few times more massive than the halos of their unobscured counterparts, a reduction in the factor of ∼10 larger halo mass as has been previously reported using WISE-selected samples. Additionally, an abundance matching analysis yields lifetimes for both obscured and unobscured quasar phases on the order of a few 100 Myr (∼ 1% of the Hubble time) -however, the obscured phase lasts roughly twice as long, in tension with many model predictions.

Composite Spectral Energy Distributions and Infrared–Optical Colors of Type 1 and Type 2 Quasars

“…In this section we examine the observed colors of the SDSS QSO 1 and 2 populations and explore how the observed colors of the model SEDs in Section 4 vary with redshift. Here we focus on colors from WISE and SDSS, which are among the largest-area MIR and optical surveys with the depth required to detect obscured quasars to z 1 > (e.g., Assef et al 2013;DiPompeo et al 2014DiPompeo et al , 2015.…”

“…To compare to these selection criteria, in Figure 8(a) we show the observed W1 W2 -and W2 W3 -colors for the SDSS QSO 1s and QSO 2s, along with the distribution for WISE sources with W3 detections and W2 < 15.05 (Vega), as selected in recent studies of WISE quasars (DiPompeo et al 2014(DiPompeo et al , 2015. Almost all (98%) of the QSO 1s and roughly half (49%) of QSO 2s have red W1 W2 -colors that would be selected by a cut of W1 W2 0.7 > -(Vega).…”

“…The completion of the Wide-field Infrared Survey Explorer (WISE; Wright et al 2010) survey of the full sky has allowed us to make dramatic progress in statistical studies of AGNs (e.g., Mor & Trakhtenbrot 2011;Donoso et al 2012;Edelson & Malkan 2012;Eisenhardt et al 2012;Ichikawa et al 2012;Mateos et al 2012;Plotkin et al 2012;Sajina et al 2012;Stern et al 2012;Assef et al 2013;Geach et al 2013;DiPompeo et al 2014DiPompeo et al , 2015DiPompeo et al , 2016DiPompeo et al , 2017Assef et al 2015Assef et al , 2017Secrest et al 2015). In particular, WISE enables us to detect and characterize hundreds of thousands of obscured quasars, increasing the sizes of obscured quasar samples by two orders of magnitude and allowing the first large statistical studies of their properties.…”

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

“…We run our growth simulations from 0 < z < 3, but we restrict "observed" samples to the range 0.5 < z < 1.5, where the bulk of objects selected from WISE colors lie (e.g. Stern et al 2012;Assef et al 2013;DiPompeo et al 2014bDiPompeo et al , 2015.…”

“…Lacy et al 2004;Treister et al 2004;Stern et al 2005;Hickox et al 2007Hickox et al , 2009Hickox et al , 2011Stern et al 2012;Hainline et al 2014;DiPompeo et al 2014b;Hickox et al 2014;Lacy et al 2015;DiPompeo et al 2015; that has historically been dominated by optically detected unobscured systems (e.g. Croom et al 2004Croom et al , 2005Richards et al 2006a,b;Myers et al 2007;Croom et al 2009;Ross et al 2009;Shen et al 2009;Bonoli et al 2009;Eftekharzadeh et al 2015).…”