Quantification of molecular cloud structure using the Δ -variance

Details Quantification of molecular cloud structure using the Δ -variance Quantification of molecular cloud structure using the Δ -variance

Oct 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...196.6303b&link_type=abstract

American Astronomical Society, 196th AAS Meeting, #63.03; Bulletin of the American Astronomical Society, Vol. 32, p.1285

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Scientific paper

We present a quantitative study of the spatial structure in observed molecular cloud images using the Δ -variance. Introduced by Stutzki et al. (1998), the Δ -variance allows to study the spatial drift behaviour of scalar functions, such as the intensity distribution of molecular cloud tracers. For images with a power law power spectrum and random phases, known as fractional Brownian motion (fBm) structures, the Δ -variance analysis allows to determine the spectral index β of the power spectrum. Compared to the power spectrum itself, the Δ -variance is more robust with respect to edge-effects. We apply the Δ -variance to spectral line maps observed in the rotational transitions of 12CO and 13CO. For the velocity integrated maps, the spatial structure of the emission is well characterized by a power law power spectrum. We find that the spectral index is remarkably uniform for different molecular clouds and linear scales larger than ~0.5 pc (2.5<=β <=2.8). Significantly larger indices (β ⪆3 ) are found for observations made at higher spatial resolution toward the Polaris Flare, a translucent cloud at high galactic latitudes, suggesting that the structure is soother at smaller scales. Preliminary results of a Δ -variance study for individual channel maps suggest a systematic variation of the power spectral index across the line profile, with steeper indices found for the channel maps at velocities close to the line center. This work is supported by the Deutsche Forschungsgemeinschaft through grant SFB301 and SFB494. F.B. is supported by the Deutsche Argentur für Luft- und Raumfahrt, DLR (grant No. 5000 99011)

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