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

Abstract

Context. Modern versions of the Miller-Urey experiment claim that formamide (NH<SUB>2</SUB>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 and in external galaxies. <BR /> Aims: How NH<SUB>2</SUB>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. <BR /> Methods: We used the NOrthern Extended Millimeter Array (NOEMA) interferometer to image NH<SUB>2</SUB>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. <BR /> Results: We report the first spatially resolved image (size 9″, 2300 AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM ≃ 5 km s<SUP>-1</SUP>. A column density of N<SUB>NH<SUB>2</SUB>CHO</SUB> = 8 × 10<SUP>12</SUP> cm<SUP>-1</SUP> and an abundance, with respect to H-nuclei, of 4 × 10<SUP>-9</SUP> 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 a gas-phase chemical process and not on grain surfaces as previously suggested. <BR /> Conclusions: The Seeds of Life in Space (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. <P />The reduced datacube is only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/L3">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/L3