Zeeman measurements of the magnetic fields at the Galactic center

There is mounting evidence that suggests magnetic fields are important in a range of phenomena observed in the Galactic center. We report here Zeeman measurements of the magnetic field in the dense molecular gas in the "circumnuclear disk" (CND; inner radius ∼1.7 pc) using the 1667 MHz OH absorption against the continuum radio source at the Galactic center (Sgr A). These observations with a resolution of 3″ × 4″ (∼0.15 pc at 8 kpc) were made with the Very Large Array. For the absorbing OH gas identifiable with the southern part of the CND, we measure a Zeeman splitting corresponding to B cos θ = -2.0 mG (B pointing toward us) at a 7 σ confidence level. Similarly, in the northern part of the CND, we again measure -2 mG, but at a marginal 4 σ level. In the other OH clouds within the central few hundred pc, 3 σ upper limits to B cos θ are typically ∼1-3 mG. These Zeeman measurements of the magnetic field strength in the neutral gas in the central region provide direct comparison with the magnetic field strengths inferred from polarimetric measurements and place constraints on models of the Galactic center involving magnetic fields.