First interstellar detection of OH

The Atacama Pathfinder Experiment (APEX) 12m 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 as well as absorption from diffuse clouds in intervening spiral arms in a velocity range from -116 to 38.5 km/s is observed. The total OH+ column density of absorbing gas is 2.4 \times 10^15 cm-2. A column density local to Sgr B2(M) of 2.6 \times 10^14 cm-2 is found. On the intervening line-of-sight the column density per unit velocity interval are in the range from 1 to 40 \times 10^12 cm-2/(km/s). 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 to be in the range of 10^1-2 and 10^3-4, respectively. The detected absorption of a continuous velocity range on the line-of-sight shows OH+ to be an abundant component of diffuse clouds.

[1]  Y. Beletsky,et al.  The relation between column densities of interstellar OH and CH molecules , 2009, 0911.4945.

[2]  J. Dickey,et al.  Cold atomic gas in the inner Galaxy , 1989 .

[3]  C. Kasemann,et al.  The APEX digital Fast Fourier Transform Spectrometer , 2006 .

[4]  W. Ip,et al.  Ion composition and dynamics at comet Halley , 1986 .

[5]  A. Benz,et al.  X-ray chemistry in the envelopes around young stellar objects , 2004, astro-ph/0412281.

[6]  Howard A. Smith,et al.  The Far-Infrared Spectrum of Arp 220 , 2004, astro-ph/0406427.

[7]  P. Verhoeve,et al.  Submillimeter spectroscopy on OH(+) - The rotational transition at 1 THz , 1985 .

[8]  F. Motte,et al.  A Molecular Line Survey of Orion KL in the 350 Micron Band , 2005 .

[9]  C. Vastel,et al.  Infrared Space Observatory Long Wavelength Spectrometer Observations of C+ and O0 Lines in Absorption toward Sagittarius B2 , 2002 .

[10]  John H. Black,et al.  Comprehensive models of diffuse interstellar clouds : physical conditions and molecular abundances , 1986 .

[11]  Holger S. P. Müller,et al.  The Cologne Database for Molecular Spectroscopy, CDMS: a useful tool for astronomers and spectroscopists , 2005 .

[12]  J. Goicoechea,et al.  The ISO LWS high-resolution spectral survey towards Sagittarius B2 , 2003, astro-ph/0702725.

[13]  H Germany,et al.  Oxygen isotopic ratios in galactic clouds along the line of sight towards Sagittarius B2 , 2005, astro-ph/0504174.

[14]  Catherine J. Cesarsky,et al.  The Atacama Pathfinder EXperiment (APEX) : a new submillimeter facility for southern skies , 2006 .

[15]  H. Werner,et al.  Molecular properties from MCSCF‐SCEP wave functions. I. Accurate dipole moment functions of OH, OH−, and OH+ , 1983 .

[16]  H. Pickett,et al.  Water in dense molecular clouds , 1991 .

[17]  W. Langer,et al.  Abundances of simple oxygen-bearing molecules and ions in interstellar clouds , 1976 .

[18]  The line-of-sight distribution of water in the SgrB2 complex , 2003, astro-ph/0303004.

[19]  M. Harwit,et al.  Observations of Absorption by Water Vapor toward Sagittarius B2 , 2000 .