13CO and C 18O Maps of N-Body Magnetohydrodynamic Simulations of Dark Clouds

Details 13CO and C 18O Maps of N-Body Magnetohydrodynamic Simulations of Dark Clouds 13CO and C 18O Maps of N-Body Magnetohydrodynamic Simulations of Dark Clouds

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...416..218s&link_type=abstract

Astrophysical Journal v.416, p.218

Astronomy and Astrophysics

Astronomy

12

Ism: Clouds, Ism: Kinematics And Dynamics, Ism: Molecules, Line: Profiles

Scientific paper

We present detailed 13CO and C18O J = 1-0 line profiles of N-body, MHD simulations of dark clouds as well as their corresponding integrated intensity and velocity maps. We start from a uniform, magnetically subcritical model of mass 1.3 × 103 Msun that is agitated by a spectrum of Alfvén waves with velocities scaling as υ ∝ λβ. This wave index β is the only tunable parameter in our simulations. We allow the initial state to relax for several dynamical time scales. All of our profiles and maps correspond to models that have scaled radii of 2 pc and mean densities of 103 cm-3, characteristic of dark clouds.
We find our line profiles to be in good agreement with those of observed dark clouds. While generally Gaussian, many profiles have two or three components; broad wings are uncommon since the relative velocity of colliding clumps is subvirial. The CO spectra are the consequences of line-of-sight overlapping and of clump-clump collisions that occur within the cloud, and which are responsible for the formation of the cloud clump-mass spectrum.
We find that dense clumps with peak densities of 104 cm-3 form in all of our models and have the general attributes of dense cores. The most profound effect of the wave spectrum is to control the shape of the cores in our simulated clouds. We find that the cores produced in the flat spectral models (β ≤ 1) had typical axial ratios of 0.7, while axial ratios of 0.5 typify the cores produced in steep spectral models β > 1. The latter result is in excellent agreement with the observations. Elongated filaments also are more prevalent in the steeper spectral models. Typical velocity gradients in these models are 0.5 km s-1 pc-1 and arise as a consequence of the wave field in the cloud. Our steep-spectrum results are consistent with the observed properties of dark clouds and their substructures.

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