Tracing differential reddening with Diffuse Interstellar Bands. The globular cluster M 4 as a testbed

TL;DR

This study demonstrates that diffuse interstellar bands, specifically at 6614 Å, can effectively trace small-scale variations in Galactic interstellar reddening, using data from the globular cluster M4 and supporting their utility in ISM structure mapping.

Contribution

It introduces a method to use DIBs at 6614 Å to map differential reddening, validated with archival data and Planck images, advancing ISM structure analysis.

Findings

Positive correlation between DIB strength and Galactic reddening

DIBs can trace small-scale ISM structure

Supports using DIBs for detailed ISM mapping

Abstract

Diffuse interstellar bands (DIBs) are weak absorption features of interstellar origin present in the optical and infrared spectra of stars. Their use as a tool to trace the structure of the Galactic ISM is gaining relevance in the recent years. Here we present an experiment to test our ability to trace differential reddening on the plane of the sky by using the information relative to the DIB at $\lambda$6614 extracted from the spectra of cool stars. For that we made use of archive FLAMES data of the globular cluster M4, as well as WISE and Planck images for reference. We found a global positive trend between the distribution of the strength of the DIB, as traced by its equivalent width, and the amount of Galactic reddening, as traced by Planck. This result supports the use of DIBs to trace the small scale structure of the Galactic ISM.