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Multiwavelength observations of active galactic nuclei (AGNs) often reveal various time-scales of variability. Among these phenomena, 'changing-look AGNs' are extreme cases where broad emission lines become faint/bright or even disappear/emerge between multi-epoch observations, providing crucial information about AGN internal structures. We here focus on 'changing-state' AGNs, specifically investigating the transition of optical spectra over years to tens of years. Based on the axisymmetric radiation-hydrodynamic simulations (Paper I) for the gas dynamics within the dust sublimation radius, we investigate the spectral properties of ionized gas exposed to the radiation from an AGN with a 107 M⊙ supermassive black hole. We find significant time-dependent variations in the Balmer emission lines by utilizing post-process pseudo-three-dimensional calculations and the spectral synthesis code cloudy. The equivalent width of H α and H β changes by a factor of 3, or the emission lines even disappear during 30 yr for the same viewing angle. The time-dependent behaviour arises primarily from gas dynamics, particularly the formation of non-steady, radiation-driven outflows within the innermost region of the disc (r ≲ 10−3 pc). The intricate interplay between non-spherical radiation sources at the core of AGNs and the dynamic behaviour of gas within the dust sublimation radius gives rise to radiation-driven outflows. This non-steady outflow potentially contributes to the observed variability in Balmer line emissions over multiyear time-scales in certain AGNs. [ABSTRACT FROM AUTHOR]

We investigated dusty and dust-free gas dynamics for a radiation-driven sub-parsec-scale outflow in an active galactic nucleus (AGN) associated with a supermassive black hole 107 M ⊙ and bolometric luminosity 1044 erg s−1 based on the two-dimensional radiation-hydrodynamic simulations. A radiation-driven "lotus-like" multi-shell outflow is launched from the inner part (r ≲ 0.04 pc) of the geometrically thin disk, and it repeatedly and steadily produces shocks as mass accretion continues through the disk to the center. The shape of the dust sublimation radius is not spherical and depends on the angle (θ) from the disk plane, reflecting the nonspherical radiation field and nonuniform dust-free gas. Moreover, we found that the sublimation radius of θ ∼ 20°–60° varies on a timescale of several years. The "inflow-induced outflow" contributes to the obscuration of the nucleus in the sub-parsec region. The column density of the dust-free gas is N H ≳ 1022 cm−2 for r ≲ 0.04 pc. Gases near the disk plane (θ ≲ 30°) can be the origin of the Compton-thick component, which was suggested by the recent X-ray observations of AGNs. The dusty outflow from the sub-parsec region can be also a source of material for the radiation-driven fountain for a larger scale. [ABSTRACT FROM AUTHOR]

Dust-obscured galaxies (DOGs), which are observationally characterized as faint in the optical and bright in the infrared, are the final stage of galaxy mergers and are essential objects in the evolution of galaxies and active galactic nuclei (AGNs). However, the relationship between the torus-scale gas dynamics around AGNs and the DOGs’ lifetime remains unclear. We obtained the evolution of the spectral energy distributions (SEDs) of a galaxy merger system with AGN feedback from postprocessed pseudo-observations based on an N -body/smoothed particle hydrodynamics (SPH) simulation. We focused on a late-stage merger of two identical galaxies with a supermassive black hole (SMBH) of 108 M ⊙. We found that the infrared luminosity of the system reaches ultra- and hyperluminous infrared galaxy classes (1012 and 1013 L ⊙, respectively). The DOG phase corresponds to a state in which the AGNs are buried in dense gas and dust, with the infrared luminosity exceeding 3.3 × 1012 L ⊙. We also identified subcategories of DOGs, namely bump and power-law DOGs, from the SEDs and their evolution. The bump DOGs tend to evolve to power-law DOGs over several Myrs. We found that contribution from the hot dust around the nucleus in the infrared radiation is essential for identifying the system as a power-law DOG; the gas and dust are distributed nonspherically around the nucleus, therefore, the observed properties of DOGs depend on the viewing angle. In our model, the lifetime of merger-driven DOGs is less than 4 Myr, suggesting that the observed DOG phase is a brief aspect of galaxy mergers. [ABSTRACT FROM AUTHOR]

To investigate the origins of the warm absorbers in active galactic nuclei (AGNs), we study the ionization-state structure of the radiation-driven fountain model in a low-mass AGN and calculate the predicted X-ray spectra utilizing the spectral synthesis code Cloudy. The spectra show many absorption and emission line features originating in the outflowing ionized gas. The O viii 0.654 keV lines are produced mainly in the polar region much closer to the supermassive black hole than the optical narrow-line regions. The absorption measure distribution of the ionization parameter (Îľ) at a low inclination spreads over 4 orders of magnitude in Îľ, indicating the multiphase ionization structure of the outflow, as actually observed in many type 1 AGNs. We compare our simulated spectra with the high energy resolution spectrum of the narrow-line Seyfert 1 galaxy NGC 4051. The model reproduces slowly outflowing (a few hundred kilometers per second) warm absorbers. However, the faster components with a few thousand kilometers per second observed in NGC 4051 are not reproduced. The simulation also underproduces the intensity and width of the O viii 0.654 keV line. These results suggest that the ionized gas launched from subparsec or smaller regions inside the torus, which is not included in the current fountain model, must be an important ingredient of the warm absorbers with a few thousand kilometers per second. The model also consistently explains the Chandra/HETG spectrum of the Seyfert 2 galaxy Circinus. [ABSTRACT FROM AUTHOR]

In Wada et al. (2019), we proposed for the first time that a new class of planets, blanets, can be formed around supermassive black holes in the galactic center. Here, we investigate the dust coagulation processes and physical conditions of the blanet formation outside the snowline (rsnow ∼ several parsecs) in more detail, especially considering the effect of the radial drift of the dust aggregates. We found that a dimensionless parameter , where vt is the turbulent velocity and cs is the sound velocity, describing the turbulent viscosity should be smaller than 0.04 in the circumnuclear disk to prevent the destruction of the aggregates due to collision. The formation timescale of blanets τGI at rsnow is, τGI ≃ 70–80 Myr for α = 0.01 − 0.04 and MBH = 106M⊙. The mass of the blanets ranges from ∼20ME to 3000ME in r < 4 pc for α = 0.02 (ME is the Earth mass), which is in contrast with 4ME–6ME for the case without the radial drift. Our results suggest that blanets could be formed around relatively low-luminosity active galactic nuclei (Lbol ∼ 1042 erg s−1) during their lifetime (≲108 yr). [ABSTRACT FROM AUTHOR]

We studied the magnetic field structures and dynamics of magnetized multiphase gas on parsec scales around supermassive black holes by using global 3D magnetohydrodynamics (MHD) simulations. We considered the effect of radiative cooling and X-ray heating due to active galactic nuclei (AGNs). The gas disk consists of a multiphase gas with (1) cold (≤103 K) and thin, and (2) warm (∼104 K) and thick components with a wide range of number densities. The turbulent magnetic energy at maximum is comparable to the thermal and turbulent kinetic energies in the turbulent motion. We confirmed that the turbulent velocity of the warm gas in the ambient cold gas is caused by magnetoconvective instability. The turbulent magnetic field due to magnetorotational instability (MRI) is developed in the disk, but the mean toroidal magnetic field dominates and supports in a quasi-steady state, where the plasma-β, the ratio between gas pressure and magnetic pressure, is low (β < 1). As often seen in adiabatic MHD simulations of rotating disks, the direction of the mean toroidal field periodically reverses with time even in multiphase gas structures. The direction reversal is caused by magnetic flux vertically escaping from the disk and by the combination of the MRI and the Parker instability. [ABSTRACT FROM AUTHOR]

We present ALMA ∼0.″02 resolution observations of the nucleus of the nearby (∼14 Mpc) type 2 active galactic nucleus NGC 1068 at HCN/HCO+/HNC J = 3–2 lines, as well as at their 13C isotopologue and vibrationally excited lines, to scrutinize the morphological, dynamical, chemical, and physical properties of dense molecular gas in the putative dusty molecular torus around a mass-accreting supermassive black hole. We confirm almost east–west-oriented dense molecular gas emission both morphologically and dynamically, which we regard as coming from the torus. Bright emission is compact (≲3 pc), and low-surface-brightness emission extends out to 5–7 pc. These dense molecular gas properties are not symmetric between the eastern and western torus. The HCN J = 3–2 emission is stronger than the HCO+J = 3–2 emission within the ∼7 pc torus region, with an estimated dense molecular mass of (0.4–1.0) × 106 M⊙. We interpret that HCN abundance is enhanced in the torus. We detect signatures of outflowing dense molecular gas and a vibrationally excited HCN J = 3–2 line. Finally, we find that in the innermost (≲1 pc) part of the torus, the dense molecular line rotation velocity, relative to the systemic velocity, is the opposite of that in the outer (≳2 pc) part, in both the eastern and western torus. We prefer a scenario of counter-rotating dense molecular gas with innermost almost Keplerian rotation and outer slowly rotating (far below Keplerian) components. Our high-spatial-resolution dense molecular line data reveal that torus properties of NGC 1068 are much more complicated than the simple axisymmetrically rotating torus picture in the classical active galactic nucleus unification paradigm. [ABSTRACT FROM AUTHOR]

It is widely believed that, in active galactic nuclei (AGNs), a supermassive black hole with an accretion disk is surrounded by an optically and geometrically thick torus at sub-parsec scale. However, it is not clear how the mass supply is toward the central engine caused and how it is related with the internal structures of the tori. The magnetic field in the tori may contribute to the accretion process via the magneto-rotational instability (MRI). Using global three-dimensional magnetohydrodynamic (MHD) simulations taking the effects of X-ray heating and radiative cooling into account studied the numerical resolution for azimuthal direction for MRI driving. We found that a strongly magnetized disk consisted of a cold (< 10 3 K) and warm ( 10 4 K) gas is developed in about 30 rotational periods. We also found in a high resolution model that the mean azimuthal magnetic fields reverse their direction quasi-periodically. We confirmed that the typical wave length of the MRI should be resolved with a least 20 azimuthal grid cells. [ABSTRACT FROM AUTHOR]