Nonisothermal filaments in equilibrium

Context. The physical properties of the so-called Ostriker isothermal filament have been classically used as a benchmark to interpret the stability of the filaments observed in nearby clouds. However, recent continuum studies have shown that the internal structure of the filaments depart from the isothermality, typically exhibiting radially increasing temperature gradients. Aims. The presence of internal temperature gradients within filaments suggests that the equilibrium configuration of these objects should be therefore revisited. The main goal of this work is to theoretically explore how the equilibrium structure of a filament changes in a nonisothermal configuration. Methods. We solve the hydrostatic equilibrium equation by assuming temperature gradients similar to those derived from observations. Results. We obtain a new set of equilibrium solutions for nonisothermal filaments with both linear and asymptotically constant temperature gradients. For sufficiently large internal temperature gradients, our results show that a nonisothermal filament could present significantly larger masses per unit length and shallower density profiles than the isothermal filament without collapsing by its own gravity. Conclusions. We conclude that filaments can reach an equilibrium configuration under nonisothermal conditions. Detailed studies of both the internal mass distribution and temperature gradients within filaments are then needed to judge the physical state of filaments. © ESO, 2013.