Fragmentation of a Magnetized Filamentary Molecular Cloud Rotating around its Axis

Abstract

The dynamical instability of a self-gravitating magnetized filamentary cloud was investigated while taking account of rotation around its axis. The filamentary cloud of our model is supported against self-gravity in part by both a magnetic field and rotation. The density distribution in equilibrium was assumed to be a function of the radial distance from the axis, $ ρ_0 (r) \, = \, ρ_{\rm c} \, ( 1 \, + \, r ^2 / 8 H ^2 ) ^{-2} $, where $ ρ_{\rm c} $ and $ H $ are model parameters specifying the density on the axis and the length scale, respectively; the magnetic filed was assumed to have both longitudinal ($z$-) and azimuthal ($φ$-) components with a strength of $ B _0 (r) \, \propto \, \sqrt{ ρ_0 (r) } $. The rotation velocity was assumed to be $ v _{0φ} \, = \, Ω_{\rm c} \, r \, (1 \, + \, r ^2 / 8 H ^2 ) ^{-1/2} $. We obtained the growth rate and eigenfunction numerically for (1) axisymmetric $ ( m \, = \, 0 ) $ perturbations imposed on a rotating cloud with a longitudinal magnetic field, (2) non-axisymmetric $ ( m \, = \, 1 ) $ perturbations imposed on a rotating cloud with a longitudinal magnetic filed, and (3) axisymmetric perturbations imposed on a rotating cloud with a helical magnetic field. The fastest growing perturbation is an axisymmetric one for all of the model clouds studied. Its wavelength is $ λ_{\rm max} \, \le \, 11.14 \, H $ for a non-rotating cloud without a magnetic field, and is shorter