Three‐dimensional Structure of the Milky Way Disk: The Distribution of Stars and Dust beyond 0.35R⊙

We present a three dimensional model for the Milky Way fit to thefar-infrared (FIR) and near-infrared (NIR) data from the COBE/DIRBE instrumentfor Galactic latitudes |b| < 30 degrees and to within 20 degrees of theGalactic center. Because of the low optical depth at 240 microns, the FIRemission traces the distribution of galactic dust in the Galaxy. We model thedust distribution as due to three components: a warped exponential disk withscale length 0.28 R_sun and a flaring scale height, a spiral arm component withfour arms as traced by Galactic HII regions, and the local (Orion) arm whichproduces prominent emission features at galactic longitude l approx. 80 and-100 degrees. A Cosmic Infrared Background of 1.07 MJy/sr is recovered,consistent with previous determinations. The dust distribution is then used tocalculate absorption in J and K, and the stellar emission in these wavebands ismodeled with two components: a warped exponential disk with a scale length of0.28 R_sun and a spiral arm component dominated by two arms. This small scalelength is consistent with a maximal disk model for our Galaxy, which isinconsistent with the cuspy dark matter halos predicted in CDM models. We finddifferent amplitudes for the warp in the stars and dust, which starts withinthe Solar Circle.Comment: 58 pages, 19 figures, final version after review, accepted for publication in Ap