Dusting off the diffuse interstellar bands: DIBs and dust in extragalactic SDSS spectra

TL;DR

This study analyzes over 1.5 million extragalactic spectra to investigate the properties and distribution of Diffuse Interstellar Bands (DIBs) in the Milky Way, revealing their complex relationship with dust and their varied presence across the sky.

Contribution

It introduces a novel large-scale analysis of DIBs using SDSS spectra, showing their existence in dust-free regions and their variable correlation with dust across the sky.

Findings

DIBs correlate with dust extinction but can exist without dust.

DIBs show significant variation in correlation with dust across different sky regions.

Different DIBs are likely caused by different carriers, as indicated by their distinct spatial distributions.

Abstract

Using over a million and a half extragalactic spectra we study the properties of the mysterious Diffuse Interstellar Bands (DIBs) in the Milky Way. These data provide us with an unprecedented sampling of the skies at high Galactic-latitude and low dust-column-density. We present our method, study the correlation of the equivalent width of 8 DIBs with dust extinction and with a few atomic species, and the distribution of four DIBs - 5780.6A, 5797.1A, 6204.3A, and 6613.6A - over nearly 15000 squared degrees. As previously found, DIBs strengths correlate with extinction and therefore inevitably with each other. However, we show that DIBs can exist even in dust free areas. Furthermore, we find that the DIBs correlation with dust varies significantly over the sky. DIB under- or over-densities, relative to the expectation from dust, are often spread over hundreds of square degrees. These patches are different for the four DIBs, showing that they are unlikely to originate from the same carrier, as previously suggested.