Correlations between Dust Extinction Features across All Wavelength Scales: From Diffuse Interstellar Bands to R ( V )

Abstract Understanding variations in the dust extinction curve is imperative for using dust as a tracer of local structure in the interstellar medium, understanding dust chemistry, and performing extinction corrections. However, the extinction curve is complicated and exhibits features across a wide range of wavelength scales, from narrow atomic lines and diffuse interstellar bands (DIBs), to intermediate-scale and very broad structures (ISSs and VBSs), and the overall slope of the optical extinction curve, parameterized by R ( V ). Robust, population-level studies of variations in these features are only now possible with large, all-sky, spectroscopic surveys. However, these features are often studied independently because they require drastically different spectral resolution. In this work, we couple features with disparate wavelength scales by cross-matching precision catalogs of DIB measurements from APOGEE (7 DIBs) and Gaia RVS (1 DIB) with low-resolution extinction-curve measurements from Gaia XP. Using this combination, we demonstrate meaningful correlations between the strengths of extinction-curve features across all wavelength scales. We present a model that partially explains the excess scatter in DIB strength versus extinction and we show variation in line shapes of two DIBs as a function of R ( V ). We find that most DIBs studied in this work increase in strength with increasing R ( V ) and/or increasing ISS strength, though we found one DIB that anomalously decreases in strength with increasing R ( V ). Using the behavior of the ensemble of APOGEE DIBs, we present this as the first evidence of systematic chemical composition variation accompanying R ( V ) variation.