**AAS 206th Meeting, 29 May - 2 June 2005**

*Session 38 Interstellar Medium, H II Regions and Molecular Clouds*

Poster, Wednesday, 10:00am-7:00pm, Thursday, 9:20am-2:00pm, June 1, 2005, Ballroom A
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## [38.14] Statistics of Velocity Centroids: Effects of Correlations of Density and Velocity.

*S. Horibe, A. Esquivel, A. Lazarian (University of Wisconsin-Madison)*

Centroids of velocity from spectroscopic observations have
been widely used to study the properties of the underlying
turbulent field, however, it was not clear until recently
how density fluctuations affect the results. In a previous
work, Lazarian and Esquivel provided an analytical
description of velocity centroids. In that work the
structure function of centroids was decomposed into four
contributions: column density, integrated velocity,
``cross-terms'', and density-velocity
``cross-correlations''. From the second term (integrated
velocity) we can retrieve the spectral index of velocity. At
the same time, the contribution of column density, entirely
attainable from observations, can in principle be removed.
In this poster, we present an in-depth analysis of the
remaining terms. It is found that the ratio of the standard
deviation to the mean of density correlates with the
``cross-term''. We also introduce artificial
density-velocity ``cross-correlations''. And, for a
reasonable level of those, it is found that when velocity
centroid fails to trace velocity the ``cross-term''
contaminates the velocity statistics well before the
``cross-correlation'' term. Our results suggest that
limitations of the use of centroids to study the scaling
properties of velocity will arise primarily from the
``cross-terms''.

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

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Bulletin of the American Astronomical Society, **37** #2

© 2005. The American Astronomical Soceity.