First spiral arm detection using dynamical mass measurements of the Milky Way disk

Open Access

Table 1.

Fitted parameters of the simple spiral arm over-density model, as described in Eqs. (11) and (12), for each of the four data samples.

	$\tilde{α}$ $\tilde{\alpha}$ (deg)	${\tilde{R}}_{0}$ $\tilde{R}_0$ (kpc)	$\tilde{L}$ $\tilde{L}$ (kpc)	$\tilde{a}$ $\tilde{a}$	$\tilde{b}$ $\tilde{b}$	$\tilde{b} / (1 + \tilde{a})$ $\tilde{b}/(1+\tilde{a})$
0 < M_G ≤ 1	48.2	9.77	0.26	–0.057	0.224	0.24
1 < M_G ≤ 2	57.0	9.81	0.44	–0.059	0.206	0.22
2 < M_G ≤ 3	59.1	9.52	0.43	–0.075	0.224	0.24
3 < M_G ≤ 4	52.5	9.24	0.30	–0.017	0.173	0.18
Joint fit	57.0	9.58	0.38	–0.053	0.190	0.20

Notes. The final row is a combination of the $\tilde{a}$ $\tilde{a}$ and $\tilde{b}$ $\tilde{b}$ parameters and corresponds to the peak relative over-density as compared to the disk areas far from the spiral arm.

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