Demystifying the Infrared Emission of Type-1 AGNs from z~0 to z~6

Abstract

The accretion of supermassive black holes (SMBHs) is accompanied by large columns of dusty gas connected to the host galaxy interstellar medium, resulting in significant emission in the infrared (IR) spectral range (λ ∼1–1000 μm). IR observations of these systems provide a wealth of information to reveal the physics of active galactic nuclei (AGN) and its role in galaxy evolution. In this thesis, I present a systematic study to characterize and decipher the IR emission of Type-1 AGNs over very broad ranges of luminosity (L_{AGN,bol} ∼ 10^8 –10^14 L_⊙) and redshift (z ∼0–6) from different perspectives: (1) we have demonstrated that the intrinsic IR SEDs of type-1 quasars at z ∼0–6 have variations from hot-/warm-dust-deficient populations to the normal population and characterized the similar AGN-heated far-IR SEDs among different AGN populations; (2) By adding UV-optical obscuration and IR-reprocessed emission of an extended distribution of large dust grains to the intrinsic AGN templates, we have successfully reconciled the IR behaviors of all major populations of type-1 AGNs, including the strong polar dust emission found in several Seyfert-1 nuclei by mid-IR interferometry observations and the large SED variations among local Seyfert-1 nuclei, normal blue quasars, extremely red quasars at z ∼2–3, AGNs with mid-IR excess emission at z ∼0.7–2, hot-dust-obscured galaxies at z ∼1.5–4, and dust-free quasars at z ∼ 6, which provided critical insights on how the diverse AGN dust environment can be reflected by the different IR SED shapes; (3) With an innovative usage of the time-series data from asteroid/supernova-hunting surveys, we have developed the first mid-IR dust reverberation survey of quasars and put several important constraints on the AGN torus structures and supported the unification model; (4) Based on an accurate knowledge of galaxy and AGN IR emission, we have shown the far-IR properties of quasar host galaxies at z ∼5–6 should be similar to the low-metallicity starbursting galaxy Haro 11 and studied the quasar star formation rates and typical stellar masss when the Universe is only ∼1 Gyr old.