On the equilibrium of rotating filaments

Abstract

The physical properties of the so-called Ostriker isothermal, non-rotating filament have been classically used as benchmark to interpret the stability of the filaments observed in nearby clouds. However, such static picture seems to contrast with the more dynamical state observed in different filaments. In order to explore the physical conditions of filaments under realistic conditions, in this work we theoretically investigate how the equilibrium structure of a filament changes in a rotating configuration. To do so, we solve the hydrostatic equilibrium equation assuming both uniform and differential rotations independently. We obtain a new set of equilibrium solutions for rotating and pressure truncated filaments. These new equilibrium solutions are found to present both radial and projected column density profiles shallower than their Ostriker-like counterparts. Moreover, and for rotational periods similar to those found in the observations, the centrifugal forces present in these filaments are also able to sustain large amounts of mass (larger than the mass attained by the Ostriker filament) without being necessary unstable. Our results indicate that further analysis on the physical state of star-forming filaments should take into account rotational effects as stabilizing agents against gravity

Gravitational fragmentation caught in the act: the filamentary Musca molecular cloud

“…The external pressure is consistent with pressures needed to confine isolated globules modeled as BonnorEbert spheres (∼2-20 × 10 4 K cm −3 , Kandori et al 2005), and a factor of a couple higher than inferred for parsec-scale filaments (∼1-5 × 10 4 K cm −3 , Fischera & Martin 2012a,b). One has to recognize that the above model does not include any contribution to the observed column densities from the surrounding gas, which is required to provide the confining pressure (see the discussion in Recchi et al 2014). Thus, the use of Eq.…”

“…This cylindric envelope has a power-law radial density distribution, ρ e (r) = Cr −2 , where C is a proportionality constant. The column density profile of the envelope results then from integrating ρ e (r) along the line of sight (see, e.g., Recchi et al 2014), yielding…”

“…The details of the fragmentation process in this model depend most crucially on the line mass of the filament at its initial condition, i.e., at the equilibrium configuration. The line mass at equilibrium, and hence the fragmentation process, can be affected by the possible pressure confinement by the surrounding environment (Fischera & Martin 2012a), support provided by magnetic fields (Fiege & Pudritz 2000a,b), accretion of gas onto the filament (Heitsch 2013a,b), temperature profile (Recchi et al 2013), and rotation (Recchi et al 2014). For a more comprehensive review, we refer to André et al (2014).…”

Magnetohydrodynamic Models of Molecular Tornadoes

“…The filament rotates with constant velocity. The density inversions noted by Hansen et al (1976) and Recchi et al (2014) are absent from this special solution. Nagasawa (1987) studied the stability of non-rotating isothermal cylinders threaded by a constant, trivial axial magnetic field.…”

“…The special solution presented in Section 2.1 represents a finely tuned special case, which we now generalize. Rotation plays an important role in the morphology of molecular tornadoes as seen in observations (Matsumura et al 2012;Sofue 2007;Morris et al 2006) and past work on rotating filaments (Hansen et al 1976;Recchi et al 2014). It is useful to examine several possible rotation laws in order to accurately describe and understand the physics of molecular tornadoes.…”