2020/03/16 by E. R. Willis, R. T. Garrod, A. Belloche +4
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.1051/0004-6361/201936489
published as A&A 636, A29 (2020) · 29 pages, 24 figures, accepted for publication in Astronomy & Astrophysics
arxiv created 2020/03/16 · arxiv updated 2020/04/15
We used the EMoCA survey data to search for isocyanides in Sgr B2(N2) and their corresponding cyanide analogs. We then used the coupled three-phase chemical kinetics code MAGICKAL to simulate their chemistry. Several new species, and over 100 new reactions have been added to the network. In addition, a new single-stage simultaneous collapse/warm-up model has been implemented, thus eliminating the need for the previous two-stage models. A variable, visual extinction-dependent ζ was also incorporated into the model and tested. We report the tentative detection of CH3NC and HCCNC in Sgr B2(N2), which represents the first detection of both species in a hot core of Sgr B2. Our updated chemical models can reproduce most observed NC:CN ratios reasonably well depending on the physical parameters chosen. The model that performs best has an extinction-dependent cosmic-ray ionization rate that varies from ~2 × 10-15 s-1 at the edge of the cloud to ~1 × 10-16 s-1 in the center. Models with higher extinction-dependent ζ than this model generally do not agree as well, nor do models with a constant ζ greater than the canonical value of 1.3 × 10-17 s-1 throughout the source. Radiative transfer models are run using results of the best-fit chemical model. Column densities produced by the radiative transfer models are significantly lower than those determined observationally. Inaccuracy in the observationally determined density and temperature profiles is a possible explanation. Excitation temperatures are well reproduced for the true ``hot core'' molecules, but are more variable for other molecules such as HC3N, for which fewer lines exist in ALMA Band 3.