First interstellar detection of OH+
F. Wyrowski, K. M. Menten, R. Güsten and A. Belloche
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [wyrowski;kmenten;rguesten;belloche]@mpifr-bonn.mpg.de
Accepted: 24 May 2010
The Atacama Pathfinder Experiment (APEX) 12 m telescope was used to observe the N = 1–0, J = 0–1 ground-state transitions of OH+ at 909.1588 GHz with the CHAMP+ heterodyne array receiver. Two blended hyperfine structure transitions were detected in absorption against the strong continuum source Sagittarius B2(M) and in several pixels offset by 18´´. Both absorption from Galactic center gas and absorption from diffuse clouds in intervening spiral arms in a velocity range from –116 to 38.5 km s-1 is observed. The total OH+ column density of absorbing gas is 2.4 × 1015 cm-2. A column density local to Sgr B2(M) of 2.6 × 1014 cm-2 is found. On the intervening line-of-sight, the column density per unit velocity interval is in the range of 1 to 40 × 1012 cm-2/(km s-1). OH+ is found to be on average more abundant than other hydrides, such as SH+ and CH+. Abundance ratios of OH and atomic oxygen to OH+ are found in the range of 101-2 and 103-4, respectively. The detected absorption of a continuous velocity range on the line-of-sight shows OH+ to be an abundant component of diffuse clouds.
Key words: astrochemistry / ISM: abundances / ISM: molecules
© ESO, 2010