An Empirical Relation between Sodium Absorption and Dust Extinction

TL;DR

This study establishes a precise empirical relation between sodium absorption and dust extinction in the Milky Way, aiding more accurate extinction estimates in astronomical observations.

Contribution

It provides the first high-precision empirical correlation between NaI D absorption and dust extinction, including a practical guide for extragalactic extinction estimation.

Findings

Correlation constrained with 0.15 mag dispersion in E(B-V)

Typical sight line crosses about three dust clouds

Provides a method to estimate extinction using NaI D absorption

Abstract

Dust extinction and reddening are ubiquitous in astronomical observations and are often a major source of systematic uncertainty. We present here a study of the correlation between extinction in the Milky Way and the equivalent width of the NaI D absorption doublet. Our sample includes more than 100 high resolution spectra from the KECK telescopes and nearly a million low resolution spectra from the Sloan Digital Sky Survey (SDSS). We measure the correlation to unprecedented precision, constrain its shape, and derive an empirical relation between these quantities with a dispersion of order 0.15 magnitude in E(B-V). From the shape of the curve of growth we further show that a typical sight line through the Galaxy, as seen within the SDSS footprint, crosses about three dust clouds. We provide a brief guide on how to best estimate extinction to extragalactic sources such as supernovae, using the NaI D absorption feature, under a variety of circumstances.