Abstract
We present observational results of water vapor maser emission with our high-sensitivity 22 GHz very long baseline interferometry (VLBI) imaging of the Seyfert galaxy NGC 1068. In this ...galaxy, there are the following four nuclear radio sources; NE, C, S1, and S2. Among them, the S1 component has been identified as the nucleus while the C component has been considered as attributed to the radio jet. In our VLBI observation, we find the following two types of water maser emission at the S1 component. One is a linearly aligned component that is considered as an edge-on disk with an inner radius of 0.62 pc. The dynamical mass enclosed within the inner radius was estimated to be 1.5 × 107 M⊙ by assuming the circular Keplerian motion. Note, however, that the best-fitting rotation curve shows a sub-Keplerian rotation (v ∝ r−0.24±0.10). The other is water maser emission distributed around the rotating disk component up to 1.5 pc from the S1 component, suggesting a bipolar outflow from the S1 component. Further, we detected water maser emission in the C component for the first time with VLBI, and discovered a ring-like distribution of water maser emission. It is known that a molecular cloud is associated with the C component (both HCN and HCO+ emission lines are detected by ALMA). Therefore, the ring-like maser emission can be explained by the jet collision to the molecular cloud. However, if these ring-like water masing clouds constitute a rotating ring around the C component, it is likely that the C component also has a supermassive black hole with a mass of ∼106 M⊙ that could be supplied from a past minor merger of a nucleated satellite galaxy.
We consider accretion flows from circumbinary disks onto supermassive binary black holes on a subparsec scale of the galactic center based on a smoothed particles hydrodynamics (SPH) code. Simulation ...models are presented for four cases; that is, a circular binary and an eccentric one, each with equal and unequal masses. We find that the circumblack-hole disks are formed around each black hole regardless of the simulation parameters. There are two-step mechanisms that cause accretion flow. First, tidally induced elongation of the circumbinary disk triggers mass inflow toward two closest points on the circumbinary disk. Then, the gas is increasingly accumulated on these two points owing to the gravitational attraction of black holes. Second, when the gas can pass across the maximum loci of the effective binary potential, it starts to overflow via their two points, and freely infalls to each black hole. In circular binaries, the gas continues to be supplied from the circumbinary disk, (i.e., the gap between the circumbinary disk and the binary black hole is always closed). In eccentric cases, the mass supply undergoes periodic on/off transitions during one orbital period because of the variation of the periodic potential. The gap starts to close after the apoastron, and to open again after the next periastron passage. Due to the gap closing/opening cycles, the mass-capture rates are eventually strongly phase dependent. This could provide observable diagnosis for the presence of supermassive binary black holes in merged galactic nuclei.
We present the proper motion of the sub-parsec-scale jet in a nearby elliptical galaxy 3C 66B. Observations were made at 2.3 GHz and 8.4 GHz at 10 epochs over four years, using the Very Long Baseline ...Array for all epochs and the Effelsberg 100 m telescope for the last epoch. The 8.4 GHz images showed that the proper motion increases from 0.21 to 0.70 mas yr--1, corresponding to an apparent speed of 0.30-0.96c, with a distance from the core on a sub-parsec scale. Our investigation suggests that the apparent increase in the proper motion can be explained by changes in the viewing angle, according to a relativistic beaming model. However, we still cannot eliminate the possibility that acceleration of the jet outflow speed or changes in the emissivity profile in the two-zone jet might be found in 3C 66B.
Supermassive black hole binaries may exist in the centers of active galactic nuclei such as quasars and radio galaxies, and mergers between galaxies may result in the formation of supermassive ...binaries during the course of galactic evolution. Using the very-long-baseline interferometer, we imaged the radio galaxy 3C 66B at radio frequencies and found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 ± 0.03 years, which provides a direct detection of a supermassive black hole binary.
H$_2$O maser emission {at 22 GHz} in the circumstellar envelope is one of the good tracers of detailed physics and inematics in the mass loss process of asymptotic giant branch stars. Long-term ...monitoring of an H$_2$O maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the H$_2$O maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a 0.1 km s$^{-1}$ scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of H$_2$O masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation.However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days. KCI Citation Count: 2
We performed phase-reference very long baseline interferometry (VLBI) observations on five radio-loud narrow-line Seyfert 1 galaxies (NLS1s) at 8.4 GHz with the Japanese VLBI Network. Each of the ...five targets (RXS J08066
$+$
7248, RXS J16290
$+$
4007, RXS J16333
$+$
4718, RXS J16446
$+$
2619, and B3 1702
$+$
457) in milli-Jansky levels were detected and unresolved in milli-arcsecond resolutions, i.e., with brightness temperatures higher than
$10^7$
K. The nonthermal processes of active galactic nucleus activity, rather than starbursts, are predominantly responsible for the radio emissions from these NLS1s. Out of the nine known radio-loud NLS1s, including those chosen for this study, we found that the four most radio-loud objects exclusively have inverted spectra. This suggests a possibility that these NLS1s are radio-loud due to Doppler beaming, which can apparently enhance both the radio power and the spectral frequency.
We present measurements of the proper motion of the sub-parsec scale jet at 22 GHz in the nearby FR I galaxy 3C 66B. Observations were made using Very Long Baseline Array (VLBA) at six epochs over ...four years. A phase-referencing technique was used to improve the image quality of the weak and diffuse jet components. We find that the inner knots are almost stationary, although one of them was expected to be detected with an apparent speed of 0.2 mas yr−1, according to 8 GHz monitoring at the same observation epochs. Clear flux variations are not observed in the core at 22 GHz; in contrast, clear flux enhancement is observed in the core at 8 GHz. We discuss a possible explanation: if the jet has helical structure, the viewing angles of the jet at 8 and 22 GHz differ by a few degrees, if the jet direction is almost along our line of sight. Although these results may imply the existence of a two-zone jet, which has been suggested in certain radio galaxies, it cannot explain the fact that the jet at the higher frequency is slower than that at the lower frequency.
A radio core represents the peak of intensity in VLBI images and is located at the base of jets. It appears at different positions depending on frequencies. This is known as "core shift", caused by ...absorption of the core emission. The position of the central engine in an AGN can be estimated accurately by measuring the core shift with multifrequency and phase-referencing observations. We observed NGC 4261 using the VLBA at seven frequencies. This source is a nearby FR-I type radio galaxy at the distance of 30 Mpc and has prominent two-sided jets. We measured the core shifts in not only approaching side but also counter side of the jets. The positions of core at infinity of frequency in both side indicated to come close asymptotically to the same position, which was separated by 82+ or -6 mu as from 43 GHz core position, corresponding to 310+ or -60R sub(s)(Schwarzschild radius). This source also has another feature that there is a region affected by free-free absorption (FFA) in the vicinity of the core and toward the counter jet. Moreover, we also found the same feature in other three sources, 3C 84, Cen A and Cyg A, which are also nearby galaxies with two-sided jets and with an indication of the FFA regions. We will measure the core shifts in these sources by using same technique as NGC 4261 in order to study the structure of circumnuclear plasma, to determine the position of the central engine and to test core shifts due to FFA.
We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey Third Data Release, by a very-long-baseline ...interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network. We aimed to select BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of the quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10
$^{5}$
K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources, or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.
We present measurements of the proper motion of the sub-parsec scale jet at 22 GHz in the nearby FR I galaxy 3C 66B. Observations were made using Very Long Baseline Array (VLBA) at six epochs over ...four years. A phase-referencing technique was used to improve the image quality of the weak and diffuse jet components. We find that the inner knots are almost stationary, although one of them was expected to be detected with an apparent speed of 0.2 mas yr−1, according to 8 GHz monitoring at the same observation epochs. Clear flux variations are not observed in the core at 22 GHz; in contrast, clear flux enhancement is observed in the core at 8 GHz. We discuss a possible explanation: if the jet has helical structure, the viewing angles of the jet at 8 and 22 GHz differ by a few degrees, if the jet direction is almost along our line of sight. Although these results may imply the existence of a two-zone jet, which has been suggested in certain radio galaxies, it cannot explain the fact that the jet at the higher frequency is slower than that at the lower frequency.
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