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, ${\rho }_0(r)={\rho }_{\mathrm{c}}(1+r^2/8H^2{)}^{-2}$, where ${\rho }_{\mathrm{c}}$ 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 ($\phi$-) components with a strength of $B_0(r)\propto \sqrt{{\rho }_0(r)}$. The rotation velocity was assumed to be $v_{0\phi }={\Omega }_{\mathrm{c}}r(1+r^2/8H^2{)}^{-1/2}$. 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 ${\lambda }_{\max }\le 11.14H$ for a non-rotating cloud without a magnetic field, and is shorter

Submitted to PASJ, Latex file, 18 page + 13 figures available on request, DPNU-94-12