Very Long Baseline Interferometry imaging of H2O maser emission in the nearby radio galaxy NGC 4261

Abstract

We report dual-frequency very long baseline interferometry (VLBI) observations at 22 and 43 GHz toward the nucleus of a nearby radio galaxy NGC 4261. In particular, we present a VLBI image of the 22 GHz H2O maser line and its location in the circumnuclear region of NGC 4261. H2O maser emission is marginally detected above the three times the rms level within a velocity range of approximately 2250-2450 km/s, slightly red-shifted with respect to the systemic velocity. H2O maser emission is located approximately 1 milliarcsecond (mas) east of the brightest continuum component at 22 GHz, where the continuum spectrum is optically thick, that is at the free-free absorbed receding jet by ionized gas. A positional coincidence between H2O maser emission and an ionized gas disk implies that the H2O maser emission arises from the near side of the disk, amplifying continuum emission from the background receding jet. If the disk axis is oriented 64 degree relative to the line of sight, the H2O maser emission is expected to be at a mean radius of 0.3 pc in the disk. The broad line width of the H2O maser emission can be attributed to complex kinematics in the immediate vicinity of the supermassive black hole (SMBH), including ongoing gas infall onto the SMBH, turbulence, and outflow. This is analogous to the multi-phase circumnuclear torus model in the nearest radio-loud H2O megamaser source NGC 1052. An alternative explanation for H2O maser association is the shock region between the jet and the ambient molecular clouds. However, this explanation fails to describe the explicit association of H2O maser emission only with the free-free absorbed receding jet.

arXiv comment10 pages, 5 figures, submitted to PASJ

References in corpus (32)

• The Atlas3D project -- I. A volume-limited sample of 260 nearby early-type galaxies: science goals and selection criteria
• A Warped Accretion Disk and Wide Angle Outflow in the Inner Parsec of the Circinus Galaxy
• The Megamaser Cosmology Project. III. Accurate Masses of Seven Supermassive Black Holes in Active Galaxies with Circumnuclear Megamaser Disks
• The Geometry of and Mass Accretion Rate through the Maser Accretion Disk in NGC 4258
• An X-ray view of 82 LINERs with Chandra and XMM-Newton data
• Radiation-driven Fountain and Origin of Torus around Active Galactic Nuclei
• A Survey for H${}_2$O Megamasers in Active Galactic Nuclei -- II. A Comparison of Detected and Undetected Galaxies
• Evidence for a Geometrically Thick Self-Gravitating Accretion Disk in NGC 3079
• The Megamaser Cosmology Project: I. VLBI observations of UGC 3789
• The Flaring H2O Megamaser and Compact Radio Source in Mrk 348
• Interstellar H${}_2$O Masers from J Shocks
• Black Hole Mass Measurements of Radio Galaxies NGC 315 and NGC 4261 Using ALMA CO Observations
• VLBA Imaging of NGC 4261: Symmetric Parsec-scale Jets and the Inner Accretion Region
• Powerful Water Masers in Active Galactic Nuclei
• Positional Coincidence of H2O Maser and a Plasma Obscuring Torus in Radio Galaxy NGC 1052
• A search for extragalactic H2O maser emission towards IRAS galaxies II - Discovery of an H2O maser in the Seyfert 1 galaxy NGC 4051
• Origins of molecular clouds in early-type galaxies
• A New Hardware Correlator in Korea: Performance Evaluation using KVN observations
• In the Shadow of the Accretion Disk: Higher Resolution Imaging of the Central Parsec in NGC 4261
• Orientation and Speed of the Parsec-Scale Jet in NGC4261 (3C270)
• Gamma-ray observations of low-luminosity active galactic nuclei
• Amplitude Correction Factors of KVN Observations
• Determination of Central Engine Position and Accretion Disk Structure in NGC 4261 by Core Shift Measurements
• Discovery of a luminous water megamaser in the FRII radiogalaxy 3C403
• 22 GHz Water Maser Search in 37 Nearby Galaxies - Four New Water Megamasers in Seyfert 2 and OH Maser/Absorber Galaxies
• Water masers in Compton-thick AGN II. The high detection rate and EVN observations of IRAS 15480-0344
• Spatially Resolved HCN Absorption Features in the Circumnuclear Region of NGC 1052
• The innermost region of the water megamaser radio galaxy 3C403
• 183 GHz water megamasers in active galactic nuclei: a new accretion disk tracer
• VLBI observations of the H2O gigamaser in TXS2226-184
• A broad HCO+ absorption line associated with the circumnuclear torus of NGC 1052
• Circumnuclear dense gas disk fuelling the active galactic nucleus in the nearby radio galaxy NGC 4261