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We adopt a Bayesian X-ray spectral approach to investigate the accretion properties of unobscured (⁠|$20\lt \log (N_{\rm H}/{\rm cm}^{-2}\lt 22$|⁠) and obscured (⁠|$22\lt \log (N_{\rm H}/{\rm cm}^{-2}\lt 24$|⁠) active galactic nuclei (AGNs) to shed light on the orientation versus evolution scenarios for the origin of the obscuring material. For a sample of 3882 X-ray-selected AGN from the Chandra COSMOS Legacy, AEGIS, and CDFS extragalactic surveys, we constrain their stellar masses, |$M_\star$|⁠ , intrinsic X-ray luminosities, |$L_{\rm X}$|⁠ , obscuring column densities, |$N_{\rm H}$|⁠ , and specific accretion rates |$\lambda \propto L_{\rm X}/M_\star$|⁠. By combining these observables within a Bayesian non-parametric approach, we infer, for the first time, the specific accretion rate distribution (SARD) of obscured and unobscured AGN to |$z\approx 3$|⁠ , i.e. the probability of a galaxy with mass |$M_\star$| at redshift z hosting an AGN with column density |$N_{\rm H}$| and specific accretion rate |$\lambda$|⁠. Our findings indicate that (1) both obscured and unobscured SARDs share similar shapes, shifting towards higher accretion rates with redshift, (2) unobscured SARDs exhibit a systematic offset towards higher |$\lambda$| compared to obscured SARD for all redshift intervals, (3) the obscured AGN fraction declines sharply at |$\log \lambda _{\rm break} \sim -2$| for |$z \lt 0.5$|⁠ , but shifts to higher |$\lambda$| values with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the |$\lambda -N_{\rm H}$| plane increases with redshift. These observations provide compelling evidence for AGN 'downsizing' and radiation-regulated nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts. [ABSTRACT FROM AUTHOR]

We present the results of an optical spectroscopic survey of 46 heavily obscured quasar candidates. Objects are selected using their mid-infrared (mid-IR) colours and magnitudes from the Wide-Field Infrared Survey Explorer (WISE) anzd their optical magnitudes from the Sloan Digital Sky Survey. Candidate Active Galactic Nuclei (AGNs) are selected to have mid-IR colours indicative of quasar activity and lie in a region of mid-IR colour space outside previously published X-ray based selection regions. We obtain optical spectra for our sample using the Robert Stobie Spectrograph on the Southern African Large Telescope. 30 objects (65 per cent) have identifiable emission lines, allowing for the determination of spectroscopic redshifts. Other than one object at ɀ ~ 2.6, candidates have moderate redshifts ranging from ɀ = 0.1 to 0.8 with a median of 0.3. 21 (70 per cent) of our objects with identified redshift (46 per cent of the whole sample) are identified as AGNs through common optical diagnostics. We model the spectral energy distributions of our sample and found that all require a strong AGN component, with an average intrinsic AGN fraction at 8 µm of 0.91. Additionally, the fits require large extinction coefficients with an average E(B -- V)AGN = 17.8 (average A(V)AGN = 53.4). By focusing on the area outside traditional mid-IR photometric cuts, we are able to capture and characterize a population of deeply buried quasars that were previously unattainable through X-ray surveys alone. [ABSTRACT FROM AUTHOR]

Radio emission from radio-quiet quasars may be due to star formation in the quasar host galaxy, to a jet launched by the supermassive black hole, or to relativistic particles accelerated in a wide-angle radiatively driven outflow. In this paper, we examine whether radio emission from radio-quiet quasars is a byproduct of star formation in their hosts. To this end, we use infrared spectroscopy and photometry from Spitzer and Herschel to estimate or place upper limits on star formation rates in hosts of ∼300 obscured and unobscured quasars at z < 1. We find that low-ionization forbidden emission lines such as [Ne II] and [Ne III] are likely dominated by quasar ionization and do not provide reliable star formation diagnostics in quasar hosts, while polycyclic aromatic hydrocarbon (PAH) emission features may be suppressed due to the destruction of PAH molecules by the quasar radiation field. While the bolometric luminosities of our sources are dominated by the quasars, the 160 μm fluxes are likely dominated by star formation, but they too should be used with caution. We estimate median star formation rates to be 6-29 M☉ yr-1, with obscured quasars at the high end of this range. This star formation rate is insufficient to explain the observed radio emission from quasars by an order of magnitude, with log (Lradio, obs/Lradio, SF) = 0.6-1.3 depending on quasar type and star formation estimator. Although radio-quiet quasars in our sample lie close to the 8-1000 μm infrared/radio correlation characteristic of the star-forming galaxies, both their infrared emission and their radio emission are dominated by the quasar activity, not by the host galaxy. [ABSTRACT FROM AUTHOR]