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Probing active galactic nuclei with H2O megamasers.
J Moran1, L Greenhill, J Herrnstein
1Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA.
Summary
The study reveals a thin, warped molecular disk in galaxy NGC4258, rotating in near-Keplerian motion. This disk
Area of Science:
- Astronomy
- Astrophysics
- Galactic Dynamics
Background:
- Mildly active galaxies can host central molecular disks.
- Water masers are powerful probes of galactic nuclei.
Purpose of the Study:
- To characterize the structure and kinematics of the molecular disk in NGC4258.
- To investigate the central mass and physical conditions of the disk.
Main Methods:
- High angular and spectral resolution observations using the Very-Long-Baseline Array.
- Analysis of water vapor maser emission at 1.35-cm wavelength.
Main Results:
- The NGC4258 disk is thin, warped, and nearly edge-on, exhibiting near-Keplerian rotation.
- The central mass is estimated to be <4 x 10^6 solar masses, suggesting a black hole.
- Disk temperature is <1000 K with a toroidal magnetic field <250 mG.
Conclusions:
- The data strongly support a supermassive black hole at the center of NGC4258.
- The molecular disk is stable and accretes material, potentially powering the nuclear X-ray source.
- NGC4258 provides a unique laboratory for studying nuclear disks and black hole accretion.