A Milky Way mass model for isolated simulations

TL;DR

This paper critiques the AGORA Milky Way–mass model for producing multi-arm spirals in a strongly submaximal disk and argues that such a configuration is not representative of the majority of spiral galaxies. It presents a heavier, more realistic MW-like model with a thickened disk, a cusped bulge, and a densely compressed halo, designed to sustain $2$–$3$ arm spirals while avoiding a bar; halo compression is computed via adiabatic methods that conserve radial action. The authors provide explicit parameter values, a method to construct the halo DF under disk growth, and three downloadable N-body realizations (0.1M, 1M, and 10M disk particles) with guidance for incorporating gas. This model offers a more realistic isolated galaxy framework for testing star-formation and feedback implementations across simulation codes and resolutions, improving the relevance of code comparisons and physical insights.

Abstract

This paper presents an equilibrium model of a Milky Way-like spiral galaxy that supports open, mostly 2- and 3-arm spiral patterns but does not form a bar. It is suggested as a more realistic alternative model to that employed by the Agora collaboration; their model has a much lower disk mass and therefore forms only multi-arm spiral patterns. This improved model should enable simulations that test star-formation and feedback models in a more realistic isolated galaxy. Three versions of the same model having $2.1\times 10^5$, $2.1\times 10^6$, and $2.1\times 10^7$ particles are available for download.

Figures (4)

• Figure 1: The black curve shows the rotation curve of the agora model. The red line shows the contribution from the disk star and "gas" particles and the green line the contribution from the bulge and halo. It is evident that this model has a strongly submaximal disk.
• Figure 2: The evolution of the disk particle density in the "medium resolution" agora model. The color scale indicates the logarithm of the disk surface density. The top row shows the disk (star) particles, and the bottom the supplied gas particles, although here they are also treated as collisionless particles. The times are in Gyr and the box has a side of 42 kpc. Note the multi-arm nature of the spiral patterns that develop in the stellar disk (top row).
• Figure 3: Upper panel: The black line gives the total rotation curve of this proposed model, after halo compression. The separate contributions of the thickened disk and the combined spherical bulge and halo are indicated by the red and green lines respectively. Lower panel: the initial radial dependence of Toomre's $Q$.
• Figure 4: The first 3 Gyr of evolution of our proposed model having no gas component. The times are in Gyr and the half-widths of the frames are 20.3 kpc. Notice the strong, open spirals and the absence of a large bar.