SpiralMap: A Python library of the Milky Way's spiral arms

TL;DR

The package allows the user to both extract the 2D trace and overplot the spiral arms in Cartesian/Polar coordinates in both Heliocentric (HC) and Galactocentric (GC) frames.

Abstract

We present a library of the major spiral arm models (and maps) of the Galaxy. The package is written in Python, and allows the user to both extract the 2D trace and overplot the spiral arms in Cartesian/Polar coordinates in both Heliocentric (HC) and Galactocentric (GC) frames. The current version is a compilation of 9 models (and maps) covering a range of tracers (stars, gas). Other models can also be added upon request.

Figures (4)

• Figure 1: Cartesian projection of the Drimmel_Ceph_2024 model shown for a particular arm (Sag-Car). We show this arm in HC (a), HC with a polar grid in the background (b), and in GC frame with a polar grid in the background (c).
• Figure 2: Cartesian projections of multiple models plotted together with a polar grid in the background. We show the Taylor_Cordes_1992 & Poggio_2021 models in HC (a) and GC (b) frames, and similarly, the Drimmel_NIR_2000 & Poggio_2021 models in HC (c) and GC (d) frames.
• Figure 3: Polar projections of multiple models plotted together. We show the Taylor_Cordes_1992 & Poggio_2021 models in HC (a) and GC (b) frames, and similarly the Drimmel_NIR_2000 & Poggio_2021 models in HC (c) and GC (d) frames.
• Figure 4: An example science case where SpiralMap can be useful. Here we show two figures reproduced from K24 (with permission), comparing the residuals between a best-fit model and data, and the locations of spiral arm models in the Milky Way. Panel(a) shows the Drimmel_NIR_2000, Drimmel_Ceph_2024, & Reid_2019 overplotted together, while panel(b) shows only the Drimmel_NIR_2000 model. Both cases are shown in polar projection.