1995A&A...298..473U

The 7 nonthermal filamentary structures located in the Galactic center region (l<|1deg|) are believed to manifest strong (few mG) vertical magnetic field lines coherent over the tens of parsec scale. We investigate the nature of this large-scale component with measurements of Zeeman splitting, in the 1665 and 1667 MHz absorption lines of OH, toward 13 selected positions: Clump 2, SgrD, SgrB2 and B1, the "l=1.5deg complex", the linear and arched filaments of the Galactic center radio arc (GCRA), 1E1740.7-2942 (The Great Annihilator), the nonthermal filaments G359.54+0.18 and G359.1-0.2, and portions of the expanding molecular ring (or the innermost X₁ bar orbit). The results are surprising indeed - we detect no line-of-sight large scale magnetic field, above an average 3σ upper limit of ∼0.3mG, toward the observed positions. We conclude that the strong vertical magnetic field lines are contained in _localized bundles which are, (1) aligned nearly within the plane of the sky (±5deg), thus showing no line-of-sight B component and/or, (2) are not strongly coupled to the relatively dense (10³cm^–3) molecular gas sampled by this study.