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R. Sunyaev (MPI fuer Astrophysik, Germany & Space Research Institute, Russian Academy of Sciences, Moscow)
Large-scale bulk motions and hydrodynamic turbulence in the intergalactic gas inside clusters of galaxies significantly broaden intense X-ray emission lines. For lines of heavy ions (primarily helium-like and hydrogen-like iron ions), the hydrodynamic broadening is appreciably larger than the thermal broadening. These lines are very intense, which allows deviations from the Gaussian shape in the line profile to be investigated. The line shape proves to be an important indicator of bulk hydrodynamic processes because the cryogenic detectors of new generation X-ray observatories will have a high energy resolution (from 5eV for ASTRO-E2 to 1-2 eV for Constellation-X and XEUS).
The permitted line of helium-like iron has peculiar profile in the case of weak turbulence due to high optical depth for resonant scattering.
Another way to investigate internal motions is connected with CMB observations using SUZIE, APEX, ACT, South Pole telescopes, PLANCK spacecraft and other planned experiments. The kinematic SZ effect and the X-ray line profile carry different information about the hydrodynamic velocity distribution in clusters of galaxies and complement each other, allowing the redshift, the peculiar velocity of the cluster, and the turbulent velocity dispersion to be separated.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.