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-.
line
stars: formation
tmc-1
dark clouds
star-formation
astrochemistry
cores
ISM: clouds
observations
carbon-chain molecules
ISM: molecules
chemistry
c6h
millimeter
negative-ions
ISM: abundances
Author
M. A. Cordiner
J. V. Buckle
Eva Wirström
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
Henrik Olofsson
Chalmers, Earth and Space Sciences, Onsala Space Observatory
S. B. Charnley
V. P. Nada
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 770 1 48Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1088/0004-637x/770/1/48