0 O ct 2 00 4 A Genetic Algorithm-Based Exploration of Three Filament Models : A Case for the Magnetic Support of the G 11 . 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 850μm. We use a novel computational technique based on an advanced genetic algorithm to explore thoroughly 3 different models of self-gravitating, pressure truncated filaments and to constrain their parameters. Specifically, the models tested are the non-magnetic Ostriker (1964) model, a generalized version of the magnetic Stodólkiewicz (1963) model, and the magnetic Fiege & Pudritz (2000a) model. Previous results showed that G11.11-0.12 has a much steeper ∼ r radial density profile than other filaments, where the density varies approximately as r, and that this steep density profile is consistent with the Ostriker (1964) 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 distingished by observations. Subject headings: ISM: clouds — magnetic fields — MHD