A genetic algorithm-based exploration of three filament models: A case for the magnetic support of the G11.11-0.12 infrared-dark cloud

The G11.11-0.12 infrared-dark cloud has a filamentary appearance, both in extinction against the diffuse infrared emission of the Galactic plane and in emission at 850 mum. We use a novel computational technique based on an advanced genetic algorithm to explore thoroughly three different models of self-gravitating, pressure-truncated filaments and to constrain their parameters. Specifically, the models tested are the nonmagnetic Ostriker model, a generalized version of the magnetic Stodolkiewicz model, and the magnetic Fiege & Pudritz model. Previous results showed that G11.11-0.12 has a much steeper similar tor(-4) radial density profile than other filaments, where the density varies approximately as r(-2), and that this steep density profile is consistent with the Ostriker model. We present a more complete analysis that shows that the radial structure of G11.11-0.12 is consistent with regimes of each of these models. All of the magnetic models that agree with the data are threaded by a dominant poloidal magnetic field, and most have dynamically significant fields. Thus, G11.11-0.12 is an excellent candidate for radial support by a magnetic field that is predominantly poloidal. We predict the polarization patterns expected for both magnetic models and show that the two magnetic models produce different polarization patterns that should be distinguished by observations.