Cyanopolyyne chemistry in the L1544 prestellar core: new insights from GBT observations

Abstract

We report a comprehensive study of the cyanopolyyne chemistry in the prototypical prestellar core L1544. Using the 100m Robert C. Byrd Green Bank Telescope (GBT) we observe 3 emission lines of HC${}_3$N, 9 lines of HC${}_5$N, 5 lines of HC${}_7$N, and 9 lines of HC${}_9$N. HC${}_9$N is detected for the first time towards the source. The high spectral resolution ($\sim$ 0.05 km s${}^{-1}$) reveals double-peak spectral line profiles with the redshifted peak a factor 3-5 brighter. Resolved maps of the core in other molecular tracers indicates that the southern region is redshifted. Therefore, the bulk of the cyanopolyyne emission is likely associated with the southern region of the core, where free carbon atoms are available to form long chains, thanks to the more efficient illumination of the interstellar field radiation. We perform a simultaneous modelling of the HC${}_5$N, HC${}_7$N, and HC${}_9$N lines, to investigate the origin of the emission. To enable this analysis, we performed new calculation of the collisional coefficients. The simultaneous fitting indicates a gas kinetic temperature of 5--12 K, a source size of 80$\arcsec$, and a gas density larger than 100 cm${}^{-3}$. The HC${}_5$N:HC${}_7$N:HC${}_9$N abundance ratios measured in L1544 are about 1:6:4. We compare our observations with those towards the the well-studied starless core TMC-1 and with the available measurements in different star-forming regions. The comparison suggests that a complex carbon chain chemistry is active in other sources and it is related to the presence of free gaseous carbon. Finally, we discuss the possible formation and destruction routes in the light of the new observations.

16 pages, 7 figure, 3 tables

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Cited by in corpus (7)

• Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
• H2CN/H2NC abundance ratio: a new potential temperature tracer for the interstellar medium
• Toward Unraveling Cyanopolyyne Surface Chemistry: A Preview on Isolated Systems From HC_{3}N to Ethyl Cyanide and Propylamine
• Isotopomer-Specific Carbon Isotope Ratio of Complex Organic Molecules in Star-Forming Cores
• Chemistry of Dark Molecular Clouds
• Digging into the Massive Protostar S255IR NIRS3: A Study of Nitrogen-Bearing Molecules and Their Prebiotic Chemistry
• Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO