Online Material

Appendix A: Tracer data for spiral structure

We collected and calculated the related parameters of HII regions and giant molecular clouds (GMCs) based on the observations in the literature, and present them here in two tables.

Table A.1:   HII regions as tracers of spiral arms. Columns 1 to 3 list the Galactic longitude, Galactic latitude and velocity, taken from the reference given in Col. 4; Cols. 5 to 7 give the radio continuum flux of the HII region, observation frequency and the reference. Columns 8 to 10 give the stellar distance when available, as well as the error and the reference; Col. 11 is a note for the distance ambiguity and Col. 12 is its reference: Knear - the nearer kinematic distance is adopted; Kfar - the farther kinematic distance is adopted; Ktan - the tracer is located at the tangential point and the distance to the tangent is adopted; Kout - the object is in the outer Galaxy and only one kinematic distance is available and adopted; Cols. 13 and 14 give the kinematic distance to the Sun and distance to the Galactic Center estimated with a rotation curve with R₀=8.5 kpc,  km s^-1; Col. 15 contains the excitation parameter rescaled by the distance we adopted; Cols. 16 to 18 are the same as Cols. 13-15 but with constants R₀=8.0 kpc and  km s^-1 for kinematic distances. Columns 19 to 21 are the same as Cols. 13-15 but with constants R₀=8.4 kpc and  km s^-1 for kinematic distances.

Table A.2:   GMCs as tracers of spiral arms. Columns 1 and 2 are the Galactic longitude and latitude; Cols. 3 to 6 list velocity, the luminosity of CO emission line (in unit of 10³ K km s^-1 pc²), distance and mass of molecular cloud, which were all taken from the reference given in Col. 8; Col. 7 is the note for distance ambiguity given in this reference, used as the same convention as in Table A.1; Cols. 9 and 10 list the distances to the Sun and to the Galactic center, which are estimated by the velocity and the rotation curve with R₀=8.5 kpc and  km s^-1 when the stellar distance is unavailable; Col. 11 gives the mass of molecular clouds re-scaled by the newly estimated distance; Cols. 12-14 are the same as Cols. 9-11 but with R₀=8.0 kpc and  km s^-1. Columns 15-17 are the same as Cols. 9-11 but with R₀=8.4 kpc and  km s^-1.