2017/08/11 by Joanna Corby, Brett A. McGuire, Brett McGuire +3 · 23 citations
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Absorption (acoustics) #Analytical Chemistry (journal) #Astrochemistry #Astrophysics #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Chemistry #Environmental chemistry #Galactic Center #Galaxy #Interstellar medium #Isotope #Isotopologue #Line (geometry) #Molecular Spectroscopy and Structure #Molecular cloud #Molecule #Optics #Physics #Stars #astro-ph.GA
paper · pdf · doi:10.1051/0004-6361/201730988
published in Astronomy and Astrophysics 610, A10 (EDP Sciences)
arxiv created 2017/08/11 · openalex publication_date 2018/01/12 · arxiv updated 2018/02/14 · openalex created_date 2020/11/23 · openalex updated_date 2026/07/13
The 1–50 GHz PRebiotic Interstellar MOlecular Survey (PRIMOS) contains ~50 molecular absorption lines observed in clouds located in the line-of-sight to Sgr B2(N). The line-of-sight material is associated with diffuse and translucent clouds located in the Galactic center, bar, and spiral arms in the disk. We measured the column densities and estimate abundances, relative to H 2 , of 11 molecules and additional isotopologues observed in this material. We used absorption by optically thin transitions of c- C 3 H 2 to estimate the molecular hydrogen columns, and argue that this method is preferable to more commonly used methods. We discuss the kinematic structure and abundance patterns of small molecules including the sulfur-bearing species CS, SO, CCS, H 2 CS, and HCS + ; oxygen-bearing molecules OH, SiO, and H 2 CO; and simple hydrocarbon molecules c- C 3 H 2 , l- C 3 H, and l- C 3 H + . Finally, we discuss the implications of the observed chemistry for the structure of the gas and dust in the ISM. Highlighted results include the following. First, whereas gas in the disk has a molecular hydrogen fraction of 0.65, clouds on the outer edge of the Galactic bar and in or near the Galactic center have molecular fractions of 0.85 and >0.9, respectively. Second, we observe trends in isotope ratios with Galactocentric distance; while carbon and silicon show enhancement of the rare isotopes at low Galactocentric distances, sulfur exhibits no trend with Galactocentric distance. We also determine that the ratio of c- C 3 H 2 / c- H 13 CCCH provides a good estimate of the 12 C/ 13 C ratio, whereas H 2 CO/H 2 13 CO exhibits fractionation. Third, we report the presence of l- C 3 H + in diffuse clouds for the first time. Finally, we suggest that CS has an enhanced abundance within higher density clumps of material in the disk, and therefore may be diagnostic of cloud conditions. If this holds, the diffuse clouds in the Galactic disk contain multiple embedded hyperdensities in a clumpy structure, and the density profile is not a simple function of A V .