Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20910510r&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #105.10; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
1
Scientific paper
We use published VLBI results to investigate the statistical properties of the velocity fields traced by H2O masers in eleven galactic regions of star formation. Previous work by Strelnitski et al. (2002) established that H2O masing spots in such regions appear to probe turbulent media and demonstrated that the two-point velocity correlation functions for the line-of-sight components of velocity traced by the masers could be approximated by power laws, with the exponents near the classical Kolmogorov value of 1/3 expected for high-Reynolds number incompressible turbulence. In the present project, we undertook a more in-depth investigation of the two-point velocity correlation functions for both previously studied and new water maser sources with published VLBI maps. We confirm that the velocity correlation functions can be satisfactorily approximated by power laws for all these sources, but we observe that a single power-law fit for the whole observed span of spatial scales describes the data worse than fits applied over constrained ranges of scale. At intermediate scales, we found that the power law exponents were near the Kolmogorov value. At smaller scales, however, there was a pronounced steepening of the slopes, which may be an indication that considerable dissipation of energy in supersonic turbulence starts at spatial scales larger than both the Kolmogorov microscale and the possible dissipation scale due to the formation of random shock waves hypothesized by Strelnitski et al. (2002). At the largest scales, we found a pronounced flattening of the slopes, which we attribute to the increased relative importance of regular components of motion (expansion and/or rotation) at these scales. This project was supported by the NSF/REU grant AST-0354056 and the Nantucket Maria Mitchell Association.
Ripman Benjamin H.
Strelnitski Vladimir
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