An empirical relation between sodium absorption and dust extinction

• Published in: Monthly notices of the Royal Astronomical Society Vol. 426; no. 2; pp. 1465 - 1474
• Main Authors: Poznanski, Dovi, Prochaska, J. Xavier, Bloom, Joshua S.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21-10-2012
• Subjects: Astronomy; Correlation analysis; dust, extinction; ISM: atoms; Milky Way; Spectrum analysis
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2012.21796.x

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 Na i 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 the order of 0.15 mag 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 Na i D absorption feature, under a variety of circumstances.