Line Derived Infrared Extinction toward the Galactic Center

We derive the extinction curve toward the Galactic center (GC) from 1 to 19 μm. We use hydrogen emission lines of the minispiral observed by ISO-SWS and SINFONI. The extinction-free flux reference is the 2 cm continuum emission observed by the Very Large Array. Toward the inner 14'' × 20'', we find an extinction of A _{2.166 μm} = 2.62 ± 0.11, with a power-law slope of α = -2.11 ± 0.06 shortward of 2.8 μm, consistent with the average near-infrared slope from the recent literature. At longer wavelengths, however, we find that the extinction is grayer than shortward of 2.8 μm. We find that it is not possible to fit the observed extinction curve with a dust model consisting of pure carbonaceous and silicate grains only, and the addition of composite particles, including ices, is needed to explain the observations. Combining a distance-dependent extinction with our distance-independent extinction, we derive the distance to the GC to be R ₀ = 7.94 ± 0.65 kpc. Toward Sgr A* (r < 0farcs5), we obtain A_H = 4.21 ± 0.10, A_Ks = 2.42 ± 0.10, and A _L' = 1.09 ± 0.13.