Interstellar extinction and abundances of simple diatomic molecules

TL;DR

This study investigates the relationships between interstellar extinction and the column densities of diatomic molecules like CN, CH, and CH+ along translucent sightlines, revealing different correlations and implications for molecule formation and dust association.

Contribution

It provides new observational analysis of molecular column densities and their correlation with interstellar extinction across multiple hemispheres, highlighting differences among molecules.

Findings

CH and CH+ correlate well with E(B-V)

CN shows large scatter in correlation with E(B-V)

CH is closely related to H2 and dust

Abstract

We analyze mutual relations between interstellar extinction E(B-V) and column densities of diatomic molecules such as CN, CH and CH cation observed along translucent sightlines. Observational material acquired using five echelle spectrographs, situated in both northern and southern hemispheres, was used in this study. While column densities of CH, CH+ correlate reasonably tightly with E(B-V) the similar relation built for CN shows a large scatter. This result suggests that CH and CH+ molecules are quite well spatially correlated to interstellar dust while CN requires another conditions to be formed. The CH molecule is closely related to H_2 as it was demonstrated already; the fact is interesting since H_2 is believed to be formed on grain surfaces rather than in the gas phase.