The Optical-Infrared Extinction Curve and its Variation in the Milky Way

TL;DR

This study provides extensive new measurements of the Milky Way's dust extinction curve, revealing its relative uniformity, large-scale variations, and a strong link to dust emissivity, enhancing understanding of interstellar dust properties.

Contribution

The paper presents the largest dataset of dust extinction curves, demonstrating their near-uniformity, large-scale variations, and correlation with dust emissivity, which were previously uncharacterized.

Findings

Extinction curve well described by R(V) parameter.

Less than 1% of sight lines have R(V) > 4.

Significant large-scale variations in R(V) across the Galactic plane.

Abstract

The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium. Here we present new measurements of the dust extinction curve and its variation towards tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies. We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, 2MASS, and WISE. We find that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves described by R(V). The extinction curve is more uniform than suggested in past works, with sigma(R(V)) = 0.18, and with less than one percent of sight lines having R(V) > 4. Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in R(V) throughout the Galactic plane. These variations are on scales much larger than individual molecular clouds, indicating that R(V) variations must trace much more than just grain growth in dense molecular environments. Indeed, we find no correlation between R(V) and dust column density up to E(B-V) ~ 2. Second, we discover a strong relationship between R(V) and the far-infrared dust emissivity.