Extinction Maps towards the Milky Way Bulge: 2D and 3D Tests with APOGEE

Abstract

Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily-reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both 2D and 3D extinction maps, using independent extinction measures based on a large spectroscopic sample of stars towards the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution $H$-band APOGEE spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants towards the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, 2D bulge extinction maps and 3D extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the 2D and 3D extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.

10 pages, 12 pages, accepted for publication in AJ

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• A parametric description of the 3D structure of the Galactic Bar/Bulge using the VVV survey
• Revisiting long-standing puzzles of the Milky Way: the Sun and its vicinity as typical outer disk chemical evolution
• Mapping the Extinction Curve in 3D: Structure on Kiloparsec Scales
• An all-sky catalog of solar-type dwarfs for exoplanetary transit surveys
• Chemical trends in the Galactic Halo with APOGEE data
• The Optical -- Mid-infrared Extinction Law of the l=165 Sightline in the Galactic Plane: Diversity of Extinction Law in the Diffuse Interstellar Medium
• The Gaia-ESO Survey: Tracing interstellar extinction
• VVV WIN 1733$-$3349: a low extinction window to probe the far side of the Milky Way bulge
• Radial velocities in the outermost disk toward the anticenter
• Distance and extinction to the Milky Way spiral arms along the Galactic centre line of sight