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

TL;DR

This study evaluates the accuracy of various 2D and 3D interstellar extinction maps towards the Milky Way bulge by comparing them with independent spectroscopic extinction estimates derived from APOGEE data.

Contribution

It provides a comprehensive assessment of the reliability of existing extinction maps using high-resolution spectroscopic data and discusses the impact of stellar atmospheric models on extinction estimates.

Findings

Near+mid-IR stellar colors are the most accurate predictors of extinction.

Reliability of extinction maps varies with stellar populations and sightlines.

Stellar atmospheric models significantly influence extinction analysis.

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.