Diagnostic diagram with the NIR molecular hydrogen line ratios H2(2–1)S(1)λ2.248 μm/H2(1–0)S(1)λ2.122 μm and H2(1–0)S(2)λ2.034 μm/H2(1–0)S(0)λ2.223 μm (Mouri 1994). Apertures in the circumnuclear ring are shown in blue circles and apertures from the region within the rings in green triangles. The thermal emission from 1000 to 3000 K (solid gray curve), models for thermal UV excitation (gray circle right; Sternberg & Dalgarno 1989), nonthermal excitation (gray ellipse left; Black & van Dishoeck 1987), X-ray heating (yellow triangles; Draine & Woods 1990), and shock heating (green circle; Brand et al. 1989) are indicated for comparison.
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