A radiation transfer model for the Milky Way. II The global properties and large scale structure

TL;DR

This paper develops an axi-symmetric radiative transfer model of the Milky Way, revealing its large-scale structure, star formation rate, stellar and dust distributions, and deriving the galaxy's attenuation curve.

Contribution

It presents a novel, comprehensive radiative transfer model of the Milky Way's global properties and large-scale structure, including detailed stellar and dust distributions.

Findings

Milky Way's star formation rate is 1.25 M_sun/yr.

Identified an inner stellar disk associated with the MW's long bar.

Derived the first MW attenuation curve as a functional fit.

Abstract

We obtained an axi-symmetric model for the large-scale distribution of stars and dust in the Milky Way (MW) using a radiative transfer code that can account for the existing near-infrared (NIR)/mid-infrared/submm all-sky emission maps of our Galaxy. We find that the MW has a star-formation rate of ${ SFR}=1.25\pm0.2\,{ M}_{\odot}$/yr, a stellar mass $M_{*}=(4.9\pm 0.3)\times10^{10}\,{ M}_{\odot}$, and a specific SFR that is relatively constant with radius (except for the inner 1 kpc). We identified an inner radius $R_{ in}= 4.5$\,kpc beyond which the stellar emissivity and dust distribution fall exponentially. For $R<R_{ in}$ the emissivities fall linearly towards the centre. The old stellar populations in the disk have an exponential scalelength that increases monotonically from $h_{ s}^{ disk}(K)=2.2\pm 0.6$\,kpc in the NIR, to $h_{ s}^{ disk}(B)=3.2\pm 0.9$\,kpc at the shorter optical bands, and a scaleheight that varies with radial distance, from $z_{ s}^{ disk}(0)=140\pm 20$\,pc in the centre to $z_{ s}^{ disk}(R_{\odot})=300\pm 20$\,pc at the solar radius. The young stellar populations have a scalelength of $h_{ s}^{ tdisk}=3.2\pm 0.9$\,kpc and a scaleheight that varies from $z_{ s}^{ tdisk}(0)=50\pm 10$\,pc in the centre to $z_{ s}^{ tdisk}(R_{\odot})=90\pm 10$\,pc at the solar radius. We discovered an inner stellar disk within the central 4.5 kpc, which we associate with the extended long bar of the MW. Most of the obscured star formation happens within this inner thin disk. The diffuse dust is mainly distributed in a disk with scalelength $h_{ d}^{ disk}=5.2\pm 0.8$\,kpc and scaleheight $z_{ d}^{ disk}=0.14\pm 0.02$\,kpc. We give the first derivation of the MW attenuation curve and present it as a functional fit to the model data. We find the MW to lie in the Green Valley of the main sequence relation for spiral galaxies.