We used the Atacama Large Millimeter/Submillimeter Array (ALMA) to map the CO(3-2) and [C I](1-0) lines, as well as their underlying continuum emission, from the central ∼ 200 pc region of the Circinus galaxy that hosts the nearest type 2 Seyfert-class active galactic nucleus (AGN), with a spatial resolution of ∼ 6 − 15 pc. The lines and continuum-emitting regions consist of a circumnuclear disk (CND; 74 pc × 34 pc) and spiral arms. The distribution of the continuum emission revealed a temperature-dependent dust geometry and possibly polar dust elongation in the torus region. The molecular mass of the CND is M H2 ∼ 3 × 10 6 M ⊙ with a beam-averaged H 2 column density of ∼ 5 × 10 23 cm −2 toward the AGN position, which contributes significantly to the nuclear obscuration. The [C I](1-0)/CO(3-2) ratio at the AGN position is unusually high, suggesting an X-ray dominated region-type chemistry. We decomposed the observed velocity fields into rotational and dispersion components, and revealed multi-phase dynamic nature in the r 10 pc torus region, i.e., the diffuse atomic gas is more spatially extended along the vertical direction of the disk than the dense molecular gas. Through comparisons with our model predictions based on the radiation-driven fountain scheme, we indicate that atomic outflows are the driver of the geometrical thickness of the atomic disk. This supports the validity of the radiation-driven fountain scheme in the vicinity of this AGN, which would explain the long-lasting mystery, the physical origin of the AGN torus.

In this study, we investigate the line emissions from cold molecular gas based on our previous "radiation-driven fountain model" (Wada et al. 2016), which reliably explains the spectral energy distribution of the nearest type 2 Seyfert galaxy, the Circinus galaxy. Using a snapshot of the best-fit radiation-hydrodynamic model for the central r ≤ 16 pc, in which non-equilibrium X-ray-dominated region chemistry is solved, we conduct post-processed, non-local thermodynamic equilibrium radiation transfer simulations for the CO lines. We obtain a spectral line energy distribution with a peak around J 6, and its distribution suggests that the lines are not thermalized. However, for a given line-ofsight, the optical depth distribution is highly non-uniform between τ ν 1 and τ ν 1. The CO-to-H 2 conversion factor (X CO ), which can be directly obtained from the results, is not a constant and depends strongly on the integrated intensity, and it differs from the fiducial value for local objects. X CO exhibits a large dispersion of more than one order of magnitude, reflecting the non-uniform internal structure of a "torus." We also found that the physical conditions differ between grid cells on a scale of a few parsecs along the observed lines of sight; therefore, a specific observed line ratio does not necessarily represent a single physical state of the ISM.

For an extension of the previous work on gravitational lensing by massless braneworld black holes, we investigate their microlensing phenomena and shadows and discuss how to distinguish them from standard Schwarzschild black holes and Ellis wormholes. Microlensing is known as the phenomenon in which luminosity amplification appears when a bright object passes behind a black hole or another massive object. We find that, for the braneworld black hole as well as for the Ellis wormhole, there appears luminosity reduction just before and after the amplification. This means that observation of such a reduction would indicate the lens object is either a braneworld black hole or a wormhole, though it is difficult to distinguish one from the other by microlensing solely. Therefore, we next analyze the optical images, or shadows of the braneworld black hole surrounded by optically thin dust, and compare them to those of the Ellis wormhole. Because the spacetime around the braneworld black hole possesses unstable circular orbits of photons, a bright ring appears in the image, just as in Schwarzschild spacetime or in the wormhole spacetime. This indicates that the appearance of a bright ring does not solely confirm a braneworld black hole, a Schwarzschild, nor an Ellis wormhole. However, we find that only for the wormhole is the intensity inside the ring larger than that the outsider intensity. Therefore, with future high-resolution observations of microlensing and shadows together, we could identify the braneworld black holes if they exist.