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

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 ± 0.2 M⊙/yr, a stellar mass M* = (4.9 ± 0.3) × 1010 M⊙, and a specific SFR that is relatively constant with radius (except for the inner 1 kpc). We identified an inner radius Rin = 4.5 kpc beyond which the stellar emissivity and dust distribution fall exponentially. For R < Rin the emissivities fall linearly towards the centre. The old stellar populations in the disk have an exponential scalelength that increases monotonically from hdisks(K)=2.2±0.6 kpc in the NIR, to hdisks(B)=3.2±0.9 kpc at the shorter optical bands, and a scaleheight that varies with radial distance, from zdisks(0)=140±20 pc in the centre to zdisks(R⊙)=300±20 pc at the solar radius. The young stellar populations have a scalelength of htdisks=3.2±0.9 kpc and a scaleheight that varies from ztdisks(0)=50±10 pc in the centre to ztdisks(R⊙)=90±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 hdiskd=5.2±0.8 kpc and scaleheight zdiskd=0.14±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.