DETECTION OF HF TOWARD PKS 1830-211, SEARCH FOR INTERSTELLAR H sub(2) F super(+), AND LABORATORY STUDY OF H sub(2) F super(+) AND H sub(2) Cl super(+) DISSOCIATIVE RECOMBINATION

• Published in: The Astrophysical journal 2016-05, Vol.822 (2), p.115-115
• Main Authors: Kawaguchi, K, Muller, S, Black, J H, Amano, T, Matsushima, F, Fujimori, R, Okabayahsi, Y, Nagahiro, H, Miyamoto, Y, Tang, J
• Format: Article
• Language: English
• Subjects: Abundance; Arrays; Blazars; Density; Image detection; Infrared spectroscopy; Interstellar; Recombination reactions
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/822/2/115

We report extragalactic observations of two fluorine-bearing species, hydrogen fluoride (HF) and fluoronium (H sub(2) F super(+)), in the z= 0.89 absorber in front of the lensed blazar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array. HF was detected toward both southwest and northeast images of the blazar, with column densities >3.4 x 10 super(14) cm super(-2) and 0.18 x 10 super(14) cm super(-2), respectively. H sub(2) F super(+) was not detected, down to an upper limit (3[sigma]) of 8.8 x 10 super(11) cm super(-2) and an abundance ratio of [H sub(2) F super(+)]/[HF] [< or =, slant] 1/386. We also searched for H sub(2) F super(+) toward the Galactic sources NGC 6334 I and W51C, and toward Galactic center clouds with the Herschel HIFI spectrometer. super(6) The upper limit on the column density was derived to be 2.5 x 10 super(11) cm super(-2) in NGC 6334 I, which is 1/68 of that for H sub(2) Cl super(+). In constrast, the ortho transition of H sub(2) Cl super(+) is detected toward PKS 1830-211. To understand the small abundance of interstellar H sub(2) F super(+), we carried out laboratory experiments to determine the rate constants for the ion-electron recombination reaction by infrared time-resolved spectroscopy. The constants determined are k sub(e)(209 K) = (1.1 + or - 0.3) x 10 super(-7) cm super(3) s super(-1) and (0.46 + or - 0.05) x 10 super(-7) cm super(3) s super(-1) for H sub(2) F super(+) and H sub(2) Cl super(+), respectively. The difference in the dissociative recombination rates between H sub(2) F super(+) and H sub(2) Cl super(+) by a factor ~2 and the cosmic abundance ratio [F]/[Cl] [approximate] 1/6 are not enough to explain the much smaller abundance of H sub(2) F super(+). The difference in the formation mechanism of H sub(2) F super(+) and H sub(2) Cl super(+) in interstellar space would be a major factor in the small abundance of H sub(2) F super(+).