期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 451, 期 1, 页码 196-209出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv948
关键词
ISM: clouds; ISM: molecules; galaxies: ISM
资金
- Deutsche Forschungsgemeinschaft (DFG) [SFB 881]
- SPP (priority program) 1573
- Konrad-Adenauer-Stiftung (KAS) via their 'Promotionsforderung'
- Teragrid [TG-MCA995024]
- DFG via Emmy-Noether grant [BA 3706]
- DFG via Frontier grant of Heidelberg University - German Excellence Initiative
- Baden-Wurttemberg Foundation
- European Research Council under the European Community [339177]
We employ the Delta-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 Delta-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 (CO)-C-12 number density and the integrated intensity of both the (CO)-C-12 and (CO)-C-13 (J = 1 -> 0) lines. The spectral slopes of the Delta-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 H2 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 Delta-variance spectra. Furthermore, we report a critical density threshold of similar to 100 cm(-3) at which the Delta-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.
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