Linear proportional relationship between N(OH) and N(CH) in the diffuse interstellar medium

Abstract

It has been known that there is a linearly proportional relationship between the column densities of CH and OH measured toward bright UV-emitting stars, although there are four outliers in this relationship among the total 24 measured targets. By using the Simbad database, we investigate reasonable configurations of diffuse interstellar medium (ISM) which could explain the observed relationship. We first identify the locations of 24 targets on the celestial sphere getting the distances to them and then count the number of molecular clouds, nebulae, and peculiar stars toward the targets which could contribute to the production of OH and CH. We present the results of our search by testing three hypothetical configurations of diffuse ISM which may explain the observed relationship.