The relation between optical extinction and hydrogen column density in the Galaxy

Abstract

A linear relation between the hydrogen column density (NH) and optical extinction (AV) in the Galaxy has long been observed. A number of studies found differing results in the slope of this relation. Here, we utilize the data on 22 supernova remnants that have been observed with the latest generation X-ray observatories and for which optical extinction andor reddening measurements have been performed and find NH (cm -2) = (2.21 ± 0.09) × 1021 AV (mag). We compare our result with the previous studies and assess any systematic uncertainties that may affect these results. © 2009 RAS.