Spectra of Maser Radiation from a Turbulent, Circumnuclear Accretion Disk. II. High-Velocity Features

Details Spectra of Maser Radiation from a Turbulent, Circumnuclear Accretion Disk. II. High-Velocity Features Spectra of Maser Radiation from a Turbulent, Circumnuclear Accretion Disk. II. High-Velocity Features

Jun 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...517..682w&link_type=abstract

The Astrophysical Journal, Volume 517, Issue 2, pp. 682-691.

Physics

10

Accretion, Accretion Disks, Black Hole Physics, Galaxies: Individual (Ngc 4258), Galaxies: Nuclei, Masers, Turbulence

Scientific paper

Calculations for radiative transfer in a turbulent medium are presented that emphasize the high-velocity, spectral line features due to masing at the sides of a Keplerian disk. The focus is on understanding the highly refined observational data about the 22 GHz masers in the thin, subparsec disk around the presumed massive black hole at the nucleus of the galaxy NGC 4258. Only a minimal description of velocity irregularities in the disk-we use turbulent velocities created by statistical sampling with a Kolmogorov-like power spectrum-is necessary to obtain spectra that reflect the basic properties of the observations. A small number of sharp features are produced at the sides of the disk and are dispersed over Doppler velocities of some 200 km s^-1 as in the observations. By treating the radiation as emerging at the observed angle of 7 deg from the average plane of the disk, we demonstrate that the flux of maser radiation from the high-velocity features and from the center of the disk are compatible with the premise that the physical properties of the front and the sides of the disk are statistically equivalent. Spectra computed with rms velocities of turbulence that are equal to the speed of sound are in satisfactory agreement with the observed spectra when the 7 deg angle is included in the calculations. A limited effort is reported to examine the changes in the observed spectra with time that result from the Keplerian rotation.

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