AAS 195th Meeting, January 2000
Session 51. ISM: Theory and Modelling
Display, Thursday, January 13, 2000, 9:20am-6:30pm, Grand Hall

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[51.02] Velocity Modification of HI Spectrum and Clouds in Velocity Space

A. Lazarian (Dept. of Astronomy, Univ. of Wisconsin, Madison), D. Pogosyan (CITA, Toronto)

Emission in spectral lines can provide unique information on interstellar turbulence. Doppler shifts due to supersonic motions contain information on turbulent velocity field which is otherwise difficult to measure. However, the problem of separation of velocity and density fluctuations is far from being trivial. We use HI as a test case and calculate the emission spectrum in velocity slices of data. We derive the dependence of the emission spectrum on the statistics of velocity and density fields. We find that random velocity creates a lot of small scale structure that can erroneously be identified as clouds. We show that the shallow spectrum of intensity reported by observers may be a consequence of the velocity fluctuations with Kolmogorov-type spectrum. We calculate how the spectra vary with the change of velocity slice thickness and show that the observational 21~cm data is consistent with the explanation that the observed intensity fluctuations are generated by a turbulent velocity field. Our technique can be applied to studies of other emission lines.

The author(s) of this abstract have provided an email address for comments about the abstract: lazarian@astro.wisc.edu

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