Table 1

Best-fit parameters for our two-armed spiral emission model with different assumptions about the input parameters.

Input parameters Fitted parameters

Bar angle Pitch angle Bar radius Pitch angle 26Al drop-off 26Al vel. χ 2
α i r0 [kpc] i a vbo [km s-1]

38° 4.4 7.7° 0.35 220 ± 60 1.63
38° 5.56° 4.6 0.40 225 ± 50 1.79
20° 5.56° 4.9 0.65 240 ± 60 2.00
38° 4.1 –0.19° / 10.25° 0.01 180 ± 75 1.01

Notes. We have adopted the model with fixed α = 38° and i = 5.56°. The rightmost column shows reduced χ2 as a measure of fit quality. We also include our best-fit four-arm spiral in the bottom row.

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