MAGNETOHYDROSTATIC EQUILIBRIUM STRUCTURE AND MASS OF FILAMENTARY ISOTHERMAL CLOUD THREADED BY LATERAL MAGNETIC FIELD

Herschel observations have recently revealed that interstellar molecular clouds consist of many filaments. Polarization observations in optical and infrared wavelengths indicate that the magnetic field often runs perpendicular to the filament. In this article, we study the magnetohydrostatic configuration of isothermal gas in which the thermal pressure and the Lorentz force are balanced against the self-gravity, and the magnetic field is globally perpendicular to the axis of the filament. The model is controlled by three parameters: center-to-surface density ratio (rho(c)/rho(s)), plasma beta of surrounding interstellar gas (beta(0)), and the radius of the hypothetical parent cloud normalized by the scale-height (R'(0)), although there remains freedom in how the mass is distributed against the magnetic flux (mass loading). In the case where R'(0) is small enough, the magnetic field plays a role in confining the gas. However, the magnetic field generally has the effect of supporting the cloud. There is a maximum line-mass (mass per unit length) above which the cloud is not supported against gravity. Compared with the maximum linemass of a nonmagnetized cloud (2c(s)(2)/G, where c(s) and G represent, respectively, the isothermal sound speed and the gravitational constant), that of the magnetized filament is larger than the nonmagnetized one. The maximum linemass is numerically obtained as lambda(max) similar or equal to 0.24 Phi(c1)/G(1/2) + 1.66c(s)(2) /G, where Phi(c1) represents one half of the magnetic flux threading the filament per unit length. The maximum mass of the filamentary cloud is shown to be significantly affected by the magnetic field when the magnetic flux per unit length exceeds Phi(c1) greater than or similar to 3pc mu G(c(s)/190ms(-1))(2).