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Register a new userClustering of obscured and unobscured quasars in the Bootes field: Placing rapidly growing black holes in the cosmic web
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We present the first measurement of the spatial clustering of mid-infrared selected obscured and unobscured quasars, using a sample in the redshift range 0.7 < z < 1.8 selected from the 9 deg^2 Bootes multiwavelength survey. Recently the Spitzer Space Telescope and X-ray observations have revealed large populations of obscured quasars that have been inferred from models of the X-ray background and supermassive black hole evolution. To date, little is known about obscured quasar clustering, which allows us to measure the masses of their host dark matter halos and explore their role in the cosmic evolution of black holes and galaxies. In this study we use a sample of 806 mid-infrared selected quasars and ~250,000 galaxies to calculate the projected quasar-galaxy cross-correlation function w_p(R). The observed clustering yields characteristic dark matter halo masses of log (M_halo [h^-1 M_sun]) = 12.7^+0.4_-0.6 and 13.3^+0.3_-0.4 for unobscured quasars (QSO-1s) and obscured quasars (Obs-QSOs), respectively. The results for QSO-1s are in excellent agreement with previous measurements for optically-selected quasars, while we conclude that the Obs-QSOs are at least as strongly clustered as the QSO-1s. We test for the effects of photometric redshift errors on the optically-faint Obs-QSOs, and find that our method yields a robust lower limit on the clustering; photo-z errors may cause us to underestimate the clustering amplitude of the Obs-QSOs by at most ~20%. We compare our results to previous studies, and speculate on physical implications of stronger clustering for obscured quasars.
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Clustering measurements of obscured and unobscured quasars show that obscured quasars reside in more massive dark matter halos than their unobscured counterparts. These results are inconsistent with simple unified (torus) scenarios, but might be explained by models in which the distribution of obscuring material depends on Eddington ratio or galaxy stellar mass. We test these possibilities by constructing simple physical models to compare to observed AGN populations. We find that previously observed relationships between obscuration and Eddington ratio or stellar mass are not sufficient reproduce the observed quasar clustering results ($langle log M_{text{halo}}/M_{odot} rangle = 12.94 ^{+ 0.10}_{- 0.11}$ and $langle log M_{text{halo}}/M_{odot} rangle = 12.49 ^{+ 0.08}_{- 0.08}$ for obscured and unobscured populations, respectively) while maintaining the observed fraction of obscured quasars (30-65$%$). This work suggests that evolutionary models, in which obscuration evolves on the typical timescale for black hole growth, are necessary to understand the observed clustering of mid-IR selected quasars.
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 $langle z rangle = 0.99$ we measure a bias of $b_q = 2.67 pm 0.16$, corresponding to a halo mass of $log (M_h / M_{odot} h^{-1}) = 13.3 pm 0.1$, while for unobscured sources with $langle z rangle = 1.04$ we find $b_q = 2.04 pm 0.17$ with a halo mass $log (M_h / M_{odot} h^{-1} )= 12.8 pm 0.1$. 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 $sim$10 larger halo mass as has been previously reported using WISE-selected samples. Additionally, an abundance matching analysis yields lifetimes for both obscured and unobscured quasar phases on the order of a few 100 Myr ($sim$ 1% of the Hubble time) --- however, the obscured phase lasts roughly twice as long, in tension with many model predictions.
We present a spectroscopically complete sample of 147 infrared-color-selected AGN down to a 22 $mu$m flux limit of 20 mJy over the $sim$270 deg$^2$ of the SDSS Stripe 82 region. Most of these sources are in the QSO luminosity regime ($L_{rm bol} gtrsim 10^{12} L_odot$) and are found out to $zsimeq3$. We classify the AGN into three types, finding: 57 blue, unobscured Type-1 (broad-lined) sources; 69 obscured, Type-2 (narrow-lined) sources; and 21 moderately-reddened Type-1 sources (broad-lined and $E(B-V) > 0.25$). We study a subset of this sample in X-rays and analyze their obscuration to find that our spectroscopic classifications are in broad agreement with low, moderate, and large amounts of absorption for Type-1, red Type-1 and Type-2 AGN, respectively. We also investigate how their X-ray luminosities correlate with other known bolometric luminosity indicators such as [O III] line luminosity ($L_{rm [OIII]}$) and infrared luminosity ($L_{6 mu{rm m}}$). While the X-ray correlation with $L_{rm [OIII]}$ is consistent with previous findings, the most infrared-luminous sources appear to deviate from established relations such that they are either under-luminous in X-rays or over-luminous in the infrared. Finally, we examine the luminosity function (LF) evolution of our sample, and by AGN type, in combination with the complementary, infrared-selected, AGN sample of Lacy et al. (2013), spanning over two orders of magnitude in luminosity. We find that the two obscured populations evolve differently, with reddened Type-1 AGN dominating the obscured AGN fraction ($sim$30%) for $L_{5 mu{rm m}} > 10^{45}$ erg s$^{-1}$, while the fraction of Type-2 AGN with $L_{5 mu{rm m}} < 10^{45}$ erg s$^{-1}$ rises sharply from 40% to 80% of the overall AGN population.
The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained. Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct collapse black holes. However, their very existence and formation environment in the early Universe are still under debate, with their supposed rarity further exacerbating the problem of modeling their ab-initio formation. SMS models have shown that rapid collapse, with an infall rate above a critical value, in metal-free haloes is a requirement for the formation of a proto-stellar core which will then form an SMS. Using a radiation hydrodynamics simulation of early galaxy formation, we show the natural emergence of metal-free haloes both massive enough, and with sufficiently high infall rates, to form an SMS. We find that haloes that are exposed to both a Lyman-Werner intensity of J_LW ~ 3 J_21 and that undergo at least one period of rapid growth early in their evolution are ideal cradles for SMS formation. This rapid growth induces substantial dynamical heating, amplifying the existing Lyman-Werner suppression originating from a group of young galaxies 20 kiloparsecs away. Our results strongly indicate that structure formation dynamics, rather than a critical Lyman-Werner (LW) flux, may be the main driver of massive black hole formation in the early Universe. We find that massive black hole seeds may be much more common in overdense regions of the early Universe than previously considered with a comoving number density up to 10^-3 Mpc^-3.
We cross-correlate a cosmic microwave background (CMB) lensing map with the projected space densities of quasars to measure the bias and halo masses of a quasar sample split into obscured and unobscured populations, the first application of this method to distinct quasar subclasses. Several recent studies of the angular clustering of obscured quasars have shown that these objects likely reside in higher-mass halos compared to their unobscured counterparts. This has important implications for models of the structure and geometry of quasars, their role in growing supermassive black holes, and mutual quasar/host galaxy evolution. However, the magnitude and significance of this difference has varied from study to study. Using data from planck, wise, and SDSS, we follow up on these results using the independent method of CMB lensing cross-correlations. The region and sample are identical to that used for recent angular clustering measurements, allowing for a direct comparison of the CMB-lensing and angular clustering methods. At $z sim 1$, we find that the bias of obscured quasars is $b_q = 2.57 pm 0.24$, while that of unobscured quasars is $b_q = 1.89 pm 0.19$. This corresponds to halo masses of $log (M_h / M_{odot} h^{-1}) = 13.24_{-0.15}^{+0.14}$ (obscured) and $log (M_h / M_{odot} h^{-1}) = 12.71_{-0.13}^{+0.15}$ (unobscured). These results agree well with with those from angular clustering (well within $1sigma$), and confirm that obscured quasars reside in host halos $sim$3 times as massive as halos hosting unobscured quasars. This implies that quasars spend a significant portion of their lifetime in an obscured state, possibly more than one half of the entire active phase.
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