A subparsec-scale dense plasma torus around an active galactic nucleus is unveiled. We report on very-long-baseline interferometry (VLBI) observations at 2.3, 8.4, and 15.4 GHz towards the active galaxy NGC1052. The convex spectra of the double-sided jets and the nucleus imply that synchrotron emission is obscured through free–free absorption (FFA) by the foreground cold dense plasma. A trichromatic image was produced to illustrate the distribution of the FFA opacity. We found a central condensation of the plasma which covers about 0.1 pc and 0.7 pc of the approaching and receding jets, respectively. A simple explanation for the asymmetric distribution is the existence of a thick plasma torus perpendicular to the jets. We also found an ambient FFA absorber, whose density profile can be ascribed to a spherical distribution of the isothermal King model. The coexistence of torus-like and spherical distributions of the plasma suggests a transition from radial accretion to rotational accretion around the nucleus.

We have mapped the central region of NGC 4945 in the J = 2 → 1 transition of 12 CO, 13 CO, and C 18 O, as well as the continuum at 1.3 mm, at an angular resolution of 5 ′′ × 3 ′′ with the Submillimeter Array. The relative proximity of NGC 4945 (distance of only 3.8 Mpc) permits a detailed study of the circumnuclear molecular gas and dust in a galaxy exhibiting both an AGN (classified as a Seyfert 2) and a circumnuclear starburst in an inclined ring with radius ∼2. ′′ 5 (∼50 pc). We infer the systemic velocity ∼585 km s −1 from channel maps and PV-diagrams. We find that all three molecular lines trace an inclined rotating disk with major axis aligned with that of the starburst ring and large-scale galactic disk, and which exhibits solid-body rotation within a radius of ∼5 ′′ (∼95 pc). The rotation curve flattens beyond this radius, and the isovelocity contours exhibit an S-shaped asymmetry suggestive of a highly inclined bar as has been invoked to produce a similar asymmetry observed on larger scales. We infer an inclination for the nuclear disk of 62 • ±2 • , somewhat smaller than the inclination of the large-scale galactic disk of ∼78 • . The continuum emission at 1.3 mm also extends beyond the starburst ring, and is dominated by thermal emission from dust. If it traces the same dust emitting in the far-infrared, then the bulk of this dust must be heated by star-formation activity rather than the AGN. We discover a kinematically-decoupled component at the center of the disk with a radius smaller than 1. ′′ 4 (27 pc), but which spans approximately the same range of velocities as the surrounding disk. This component has a higher density than its surroundings, and is a promising candidate for the circumnuclear molecular torus invoked by AGN unification models.

We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in 12 CO(J = 2 -1) with the Submillieter Array (SMA). The 12 CO(J = 2 -1) map shows a central concentration and a surrounding ring, which coincide respectively with the Seyfert nucleus and a starburst ring. The line intensity peaks at the nucleus, whereas in a previously published 12 CO(J = 1 -0) map the intensity peaks at the starburst ring. The molecular ring has an azimuthally averaged 12 CO(J = 2 -1)/(J = 1 -0) intensity ratio (R 21 ) of about unity, which is similar to those in nearby active star forming galaxies, suggesting that most of the molecular mass in the ring is involved in fueling the starburst. The moleculargas-to-dynamical mass ratio in the starburst ring shows a somewhat lower value than that found in nearby star forming galaxies, suggesting that the high R 21 of unity may be caused by additional effects, such as shocks induced by gas infall along the bar. The molecular gas can last for only about 1.2 × 10 8 years without further replenishment assuming a constant star formation rate and a perfect conversion of gas to stars. The velocity map shows that the central molecular gas is rotating with the molecular ring in the same direction, while its velocity gradient is much steeper than that of the ring. This velocity gradient of the central gas is similar to what is usually observed in some Seyfert 2 galaxies. To

We present a discussion on high-resolution studies of the nuclear region of NGC 3079 using observations of an H2O maser and continuum emission as well as H I absorption with a global VLBI network including the VLBA, the phased VLA and the Effelsberg 100 m telescope. Multi-frequency observations of the continuum emission reveal the spectra of continuum components and suggest a core-jet morphology. The H2O maser spots lie in a series of clusters distributed along a north-south direction, while we rule out any possibility that the masering disk lies along the north-south direction. H I absorption features towards the continuum components have a velocity gradient opposite to that observed in the galaxy as a whole. We identify the nucleus and rotation axis of the central 10 pc region, and discuss the properties of a postulated rotating torus in the nuclear region.

We report our intensive, high-angular-resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from February 2011 to October 2012, together with contemporaneous high-energy (HE; 100 MeV< E <100 GeV) γ-ray light curves obtained by the Fermi Large Area Telescope (LAT). During this period (specifically from February 2012 to March 2012), an elevated level of the M 87 flux is reported at very-high-energy (VHE; E > 100 GeV) γ-rays by VERITAS. We detected a remarkable (up to ∼70%) increase of the radio flux density from the unresolved jet base (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. Meanwhile, we confirmed with EVN at 5 GHz that the peculiar knot HST-1, which is an alternative favored γ-ray production site located at 120 pc from the nucleus, remained quiescent in terms of its flux density and structure. These results in the radio bands strongly suggest that the VHE γ-ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. We further conducted VERA astrometry for the M 87 core at six epochs during the flaring period, and detected core shifts between 22 and 43 GHz, a mean value of which is similar to that measured in the previous astrometric measurements. We also discovered a clear frequency-dependent evolution of the radio core flare at 43, 22 and 5 GHz; the radio flux density increased more rapidly at higher frequencies with a larger amplitude, and the light curves clearly showed a time-lag between the peaks at 22 and 43 GHz, the value of which is constrained to be within ∼ 35 − 124 days. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity. By combining the obtained core shift and time-lag, we estimated an apparent speed of the newborn component propagating through the opaque region between the cores at 22 and 43 GHz. We derived a sub-luminal speed (less than ∼0.2c) for this component. This value is significantly slower than the super-luminal (∼1.1c) features that appeared from the core during the prominent VHE flaring event in 2008, suggesting that the stronger VHE activity can be associated with the production of the higher Lorentz factor jet in M 87.

We present multifrequency simultaneous VLBA observations at 15, 22, and 43 GHz toward the nucleus of the nearby radio galaxy NGC 1052. These three continuum images reveal a double-sided jet structure whose relative intensity ratios imply that the jet axis is oriented close to the sky plane. The steeply rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest that synchrotron emission is absorbed by foreground thermal plasma. We detected H 2 O maser emission in the velocity range of 1550-1850 km s À1 , which is redshifted by 50-350 km s À1 with respect to the systemic velocity of NGC 1052. The redshifted maser gas appears projected against both sides of the jet, in the same manner as the H i seen in absorption. The H 2 O maser gas is located where the free-free absorption opacity is large. This probably implies that the masers in NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus of NGC 4258. Such circumnuclear structure could be the source of accretion onto the central engine.

We have measured the annual parallax of the H 2 O maser source associated with an infrared dark cloud MSXDC G034.43+00.24 from the observations with VERA (VLBI Exploration of Radio Astrometry). The parallax is 0.643 ± 0.049 mas, corresponding to the distance of 1.56 +0.12 −0.11 kpc. This value is less than the half of the previous kinematic distance of 3.7 kpc. We revise the core mass estimates of MSXDC G034.43+00.24, based on virial masses, LTE masses and dust masses and show that the core masses decrease from the previous estimations of ∼ 1000M ⊙ to hundreds of M ⊙ . The spectral type derived from the luminosity also changes from O9.5 to B1 in the case of MM1. This spectral type is still consistent with that of the massive star. The radial velocity derived from the flat rotation model is smaller than the observed velocity, which corresponds to the peculiar motion of ∼ 40 km s −1 in the line-of-sight direction.

We investigated the jet width profile with distance along the jet in the nearby radio galaxy NGC 1052 at radial distances between ∼ 300 to 4 × 10 7 Schwarzschild Radii(R S ) from the central engine on both their approaching and receding jet sides. The width of jets was measured in images obtained with the VLBI Space Observatory Programme (VSOP), the Very Long Baseline Array (VLBA), and the Very Large Array (VLA). The jet-width profile of receding jets are apparently consistent with that of approaching jets throughout the measuring distance ranges, indicating symmetry at least up to the sphere of gravitational influence of the central black hole. The power-law index a of the jet-width profile (w jet ∝ r a , where w jet is the jet width, r is the distance from the central engine in the unit of R S ) apparently shows a transition from a ∼ 0 to a ∼ 1, i.e., the cylindrical-to-conical jet structures, at a distance of ∼ 1 × 10 4 R S . The cylindrical jet shape at the small distances is reminiscent of the innermost jets in 3C 84. Both the central engines of NGC 1052 and 3C 84 are surrounded by dense material, part of which is ionized and causes heavy free-free absorption.