Linking the dust and chemical evolution: Taurus and Perseus. New collisional rates for HCN, HNC, and their C, N, and H isotopologues
Roueff, E.; Sarazin, C. L.; Kramer, C.; Fuente, A.; Caselli, P.; Lique, F.; Kirk, J. M.; Mroczkowski, T.; Mason, B.; Rivière-Marichalar, P.; Esplugues, G.; Rodríguez-Baras, M.; Navarro-Almaida, D.; Romero, C. E.; Dicker, S.; Sievers, J.; Bop, C. T.; Chacón-Tanarro, A.; Devlin, M.; Bhandarkar, T.; Lowe, I.
France, Spain, United States, Germany, United Kingdom, Canada
Abstract
Context. HCN, HNC, and their isotopologues are ubiquitous molecules that can serve as chemical thermometers and evolutionary tracers to characterize star-forming regions. Despite their importance in carrying information that is vital to studies of the chemistry and evolution of star-forming regions, the collision rates of some of these molecules have not been available for rigorous studies in the past.
Aims: Our goal is to perform an up-to-date gas and dust chemical characterization of two different star-forming regions, TMC 1-C and NGC 1333-C7, using new collisional rates of HCN, HNC, and their isotopologues. We investigated the possible effects of the environment and stellar feedback in their chemistry and their evolution.
Methods: We used updated collisional rates of HCN, HNC, and their isotopologues in our analysis of the chemistry of TMC 1-C (Taurus) and NGC 1333-C7 (Perseus). With millimeter observations, we derived their column densities, the C and N isotopic fractions, the isomeric ratios, and the deuterium fractionation. The continuum data at 3 mm and 850 µm allowed us to compute the emissivity spectral index and look for grain growth as an evolutionary tracer.
Results: The H13CN/HN13C ratio is anticorrelated with the deuterium fraction of HCN, thus it can readily serve as a proxy for the temperature. The spectral index (β ~ 1.34-2.09) shows a tentative anticorrelation with the H13CN/HN13C ratio, suggesting grain growth in the evolved, hotter, and less deuterated sources. Unlike TMC 1-C, the south-to-north gradient in dust temperature and spectral index observed in NGC 1333-C7 suggests feedback from the main NGC 1333 cloud.
Conclusions: With this up-to-date characterization of two star-forming regions, we found that the chemistry and the physical properties are tightly related. The dust temperature, deuterium fraction, and the spectral index are complementary evolutionary tracers. The large-scale environmental factors may dominate the chemistry and evolution in clustered star-forming regions.