Publication Date:
2015-05-29
Description:
We employ the -variance analysis and study the turbulent gas dynamics of simulated molecular clouds (MCs). Our models account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas. We investigate simulations using three different initial mean number densities of n 0 = 30, 100 and 300 cm –3 that span the range of values typical for MCs in the solar neighbourhood. Furthermore, we model the CO line emission in a post-processing step using a radiative transfer code. We evaluate -variance spectra for centroid velocity (CV) maps as well as for integrated intensity and column density maps for various chemical components: the total, H 2 and 12 CO number density and the integrated intensity of both the 12 CO and 13 CO ( J = 1 -〉 0) lines. The spectral slopes of the -variance computed on the CV maps for the total and H 2 number density are significantly steeper compared to the different CO tracers. We find slopes for the linewidth–size relation ranging from 0.4 to 0.7 for the total and H 2 density models, while the slopes for the various CO tracers range from 0.2 to 0.4 and underestimate the values for the total and H 2 density by a factor of 1.5–3.0. We demonstrate that optical depth effects can significantly alter the -variance spectra. Furthermore, we report a critical density threshold of ~100 cm –3 at which the -variance slopes of the various CO tracers change sign. We thus conclude that carbon monoxide traces the total cloud structure well only if the average cloud density lies above this limit.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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