On the ubiquity of molecular anions in the dense interstellar medium
Journal article, 2013

Results are presented from a survey for molecular anions in seven nearby Galactic star-forming cores and molecular clouds. The hydrocarbon anion C6H- is detected in all seven target sources, including four sources where no anions have been previously detected: L1172, L1389, L1495B, and TMC-1C. The C6H-/C6H column density ratio is greater than or similar to 1.0% in every source, with a mean value of 3.0% (and standard deviation 0.92%). Combined with previous detections, our results show that anions are ubiquitous in dense clouds wherever C6H is present. The C6H-/C6H ratio is found to show a positive correlation with molecular hydrogen number density, and with the apparent age of the cloud. We also report the first detection of C4H- in TMC-1 (at 4.8 sigma confidence), and derive an anion-to-neutral ratio C4H-/C4H = (1.2 +/- 0.4) x 10(-5)(= 0.0012% +/- 0.0004%). Such a low value compared with C6H- highlights the need for a revised radiative electron attachment rate for C4H. Chemical model calculations show that the observed C4H- could be produced as a result of reactions of oxygen atoms with C5H- and C6H-.

ISM: clouds

ISM: molecules


stars: formation

ISM: abundances


M. A. Cordiner

NASA Goddard Space Flight Center

Catholic University of America

J. V. Buckle

University of Cambridge

Eva Wirström

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

NASA Goddard Space Flight Center

Henrik Olofsson

Chalmers, Earth and Space Sciences, Onsala Space Observatory

S. B. Charnley

NASA Goddard Space Flight Center

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 770 1 48

Subject Categories

Astronomy, Astrophysics and Cosmology



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