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Seeds of Life in Space (SOLIS) III. Formamide in protostellar shocks: evidence for gas-phase formation

2017; Cornell University; Linguagem: Inglês

C. Codella, C. Ceccarelli, P. Caselli, Nadia Balucani, V. Baroneınst, F. Fontani, B. Leflóch, L. Podio, S. Viti, Siyi Feng, R. Bachiller, E. Bianchi, F. Dulieu, I. Jiménez-Serra, Jonathan Holdship, R. Neri, J. E. Pineda, Andy Pon, Ian Sims, S. Spezzano, A. I. Vasyunin, F. O. Alves, L. Bizzocchi, S. Bottinelli, E. Caux, A. Chacón-Tanarro, R. Choudhury, A. Coutens, Cécile Favre, P. Hily-Blant, C. Kahane, A. Jaber Al-Edhari, J. Laas, A. López-Sepulcre, J. Ospina, Yoko Oya, A. Punanova, Cristina Puzzarini, D. Quenard, Albert Rimola, Nami Sakai, Dimitrios Skouteris, V. Taquet, L. Testi, P. Theulé, Piero Ugliengo, C. Vastel, Fanny Vazart, L. Wiesenfeld, Satoshi Yamamoto,

Advanced Chemical Physics Studies

Context: Modern versions of the Miller-Urey experiment claim that formamide (NH$_2$CHO) could be the starting point for the formation of metabolic and genetic macromolecules. Intriguingly, formamide is indeed observed in regions forming Solar-type stars as well as in external galaxies. Aims: How NH$_2$CHO is formed has been a puzzle for decades: our goal is to contribute to the hotly debated question of whether formamide is mostly formed via gas-phase or grain surface chemistry. Methods: We used the NOEMA interferometer to image NH$_2$CHO towards the L1157-B1 blue-shifted shock, a well known interstellar laboratory, to study how the components of dust mantles and cores released into the gas phase triggers the formation of formamide. Results: We report the first spatially resolved image (size $\sim$ 9, $\sim$ 2300 AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM $\simeq$ 5 km s$^{-1}$. A column density of $N_{\rm NH_2CHO}$ = 8 $\times$ 10$^{12}$ cm$^{-1}$, and an abundance (with respect to H-nuclei) of 4 $\times$ 10$^{-9}$ are derived. We show a spatial segregation of formamide with respect to other organic species. Our observations, coupled with a chemical modelling analysis, indicate that the formamide observed in L1157-B1 is formed by gas-phase chemical process, and not on grain surfaces as previously suggested. Conclusions: The SOLIS interferometric observations of formamide provide direct evidence that this potentially crucial brick of life is efficiently formed in the gas-phase around Sun-like protostars.