2024/08/20 by David A. Neufeld, Neufeld, David A., D. E. Welty +16 · 3 citations
Mathematics · Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Gravitation Theories #FOS: Physical sciences #Gas Dynamics and Kinetic Theory
paper · pdf · doi:10.48550/arxiv.2408.11108
openalex publication_date 2024/08/20 · openalex created_date 2024/09/29 · openalex updated_date 2026/07/28
Newly-computed collisional rate coefficients for the excitation of C2 in collisions with H2, presented recently by Najar and Kalugina (2020), are significantly larger than the values adopted previously in models for the excitation of the C2 molecule, a widely used probe of the interstellar gas density. With these new rate coefficients, we have modeled the C2 rotational distributions inferred from visible and ultraviolet absorption observations of electronic transitions of C2 towards a collection of 46 nearby background sources. The inferred gas densities in the foreground interstellar clouds responsible for the observed C2 absorption are a factor 4 to 7 smaller than those inferred previously, a direct reflection of the larger collisional rate coefficients computed by Najar and Kalugina (2020). These lower density estimates are generally in good agreement with the peak densities inferred from 3D extinction maps for the relevant sightlines. In cases where H3+ absorption has also been observed and used to estimate the cosmic-ray ionization rate (CRIR), our estimates of the latter will also decrease accordingly because the H3+ abundance is a function of the ratio of the CRIR to the gas density.