Search

In the standard quasar model, the accretion disc obscuration is due to the canonical dusty torus. Here, we argue that a substantial part of the quasar obscuration can come from the interstellar medium (ISM) when the quasars are embedded in compact starbursts. We use an obscuration-unbiased sample of 578 infrared (IR) quasars at z ≈ 1–3 and archival Atacama Large Millimetre/submillimetre Array submillimetre host galaxy sizes to investigate the ISM contribution to the quasar obscuration. We calculate star formation rates (SFR) and ISM column densities for the IR quasars and a control sample of submillimetre galaxies (SMGs) not hosting quasar activity and show that: (1) the quasar obscured fraction is constant up to |$\rm SFR\approx 300 \: {\rm M}_{\odot } \: yr^{-1}$|⁠ , and then increases towards higher SFR, suggesting that the ISM obscuration plays a significant role in starburst host galaxies, and (2) at |$\rm SFR\gtrsim 300 \: {\rm M}_{\odot } \: yr^{-1}$|⁠ , the SMGs and IR quasars have similarly compact submillimetre sizes (⁠|$R_{\rm e}\approx 0.5{\!-\!}3\,\mathrm{ kpc}$|⁠) and consequently, the ISM can heavily obscure the quasar, even reaching Compton-thick (⁠|$N_{\rm H}\gt 10^{24} \rm \: cm^{-2}$|⁠) levels in extreme cases. Based on our results, we infer that |${\approx} 10{\!-\!}30~{{ \rm per\ cent}}$| of the IR quasars with |$\rm SFR\gtrsim 300 \: {\rm M}_{\odot } \: yr^{-1}$| are obscured solely by the ISM. [ABSTRACT FROM AUTHOR]

The observed optical colors of quasars are generally interpreted in one of two frameworks: unified models that attribute the color to the random orientation of the accretion disk along the line of sight, and evolutionary models that invoke connections between quasar systems and their environments. We test these schemas by probing the dark matter halo environments of optically selected quasars as a function of g âˆ' i optical color by measuring the two-point correlation functions of ∼0.34 million eBOSS quasars as well as the gravitational deflection of cosmic microwave background photons around ∼0.66 million XDQSO photometric quasar candidates. We do not detect a trend of halo bias with optical color through either analysis, finding that optically selected quasars at 0.8 < z < 2.2 occupy halos of characteristic mass M h ∼ 3 Ă— 1012 h âˆ'1 M ⊙ regardless of their color. This result implies that a quasar’s large-scale halo environment is not strongly connected to its observed optical color. We also confirm the findings of fundamental differences in the radio properties of red and blue quasars by stacking 1.4 GHz FIRST images at their positions, suggesting the observed differences cannot be attributed to orientation. Instead, the differences between red and blue quasars likely arise on nuclear-galactic scales, perhaps owing to reddening by a nuclear dusty wind. Finally, we show that optically selected quasars’ halo environments are also independent of their r âˆ' W2 opticalâ€"infrared colors, while previous work has suggested that mid-infrared-selected obscured quasars occupy more massive halos. We discuss the implications of this result for models of quasar and galaxy coevolution. [ABSTRACT FROM AUTHOR]