The structure of the Milky Way based on unWISE 3.4$\mu$m integrated photometry

TL;DR

This paper provides a detailed 3D photometric decomposition of the Milky Way using unWISE 3.4μm data, modeling its complex structure including discs, bulge, and features like warping and dust extinction.

Contribution

It introduces a comprehensive 3D photometric model of the Milky Way that accounts for various observed features and compares favorably with external galaxy analyses.

Findings

Estimated thick disc mass is 0.4-1.3 times the thin disc mass.

Model includes disc flaring, warping, and over-densities.

Bulge modeled with N-body simulations showing X-shape structure.

Abstract

We present a detailed analysis of the Galaxy structure using an unWISE wide-field image at $3.4\mu$m. We perform a 3D photometric decomposition of the Milky Way taking into account i) the projection of the Galaxy on the celestial sphere and ii) that the observer is located within the Galaxy at the solar radius. We consider a large set of photometric models starting with a pure disc model and ending with a complex model which consists of thin and thick discs plus a boxy-peanut-shaped bulge. In our final model, we incorporate many observed features of the Milky Way, such as the disc flaring and warping, several over-densities in the plane, and the dust extinction. The model of the bulge with the corresponding X-shape structure is obtained from N-body simulations of a Milky Way-like galaxy. This allows us to retrieve the parameters of the aforementioned stellar components, estimate their contribution to the total Galaxy luminosity, and constrain the position angle of the bar. The mass of the thick disc in our models is estimated to be 0.4-1.3 of that for the thin disc. The results of our decomposition can be directly compared to those obtained for external galaxies via multicomponent photometric decomposition.