The Interstellar Line of Sight to the Interacting Galaxy NGC 5195
Adam M. Ritchey, George Wallerstein

TL;DR
This study analyzes the interstellar medium along the line of sight to NGC 5195, revealing high molecular content, significant depletion, and environmental conditions influenced by galaxy interactions through high-resolution spectral observations.
Contribution
It provides detailed spectroscopic analysis of interstellar gas in M51's outer arm toward NGC 5195, highlighting molecular fractions, depletion patterns, and environmental effects due to galaxy interactions.
Findings
High molecular fraction (~0.65) in the gas toward NGC 5195.
DIBs are weaker than expected based on K I, indicating high molecular content.
Enhanced turbulence possibly caused by M51 and companion galaxy interactions.
Abstract
We present moderately-high resolution echelle observations of the nucleus of NGC 5195, the line of sight to which samples intervening interstellar material associated with the outer spiral arm of M51. Our spectra reveal absorption from interstellar Na I, K I, Ca II, and CH+, and from a number of diffuse interstellar bands (DIBs), at a velocity close to that exhibited by H I 21 cm emission from M51 at the position of NGC 5195. The H I column density implied by the equivalent width of the 5780.5 DIB, based on the relationship between W(5780.5) and N(H I) derived for sight lines in the local Galactic interstellar medium, is consistent with the column density obtained from the integrated H I emission. The H2 column density predicted from the observed column density of K I, using the Galactic relationship between N(K I) and N(H2), is comparable to N(H I), suggesting a high molecular fraction…
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