Herschel/HIFI Discoveryof a Far-Infrared DIB Analog
Conference contribution, 2014

The Herschel Space Observatory carried out observations at far-infrared wavelengths, which significantly increased our knowledge of the interstellar medium and the star-formation process in the Milky Way and external galaxies, as well as our understanding of astrochemistry. Absorption features, known, e.g., from observations at millimeter wavelengths, are more commonly observed in the far-infrared, in particular toward strong dust continuum sources. The lowest energy transitions are not only observed at LSR-velocities related to the source, but often also at velocities associated with diffuse molecular clouds along the line of sight toward the background source. Unbiased spectral line surveys of the massive and very luminous Galactic Center sources Sagittarius B2(M) and (N) were carried out across the entire frequency range of the high-resolution Heterodyne Instrument for Far-Infrared Astronomy (HIFI). An absorption feature was detected toward both sources at about 617.531 GHz, corresponding to 20.599 cm-1, 485.47 μm, or 2.5539 meV. This feature is unique in its appearance at all velocity components associated with diffuse foreground molecular clouds, together with its conspicuous absence at velocities related to the sources themselves. The carriers of at least a substantial part of the DIBs are thought to reside in the diffuse interstellar medium. Therefore, we consider this absorption feature to be a far-infrared DIB analog. Subsequent dedicated observations confirmed that the line is present only in the foreground clouds on the line of sight toward other massive star-forming regions in the Galactic disk. There is indication that the feature has substructure, possibly of fine or hyperfine nature. Attempts to assign the feature to atomic or molecular species have been unsuccessful so far.

Author

Holger Muller

University of Cologne

P. Schilke

University of Cologne

M. Gerin

Centre national de la recherche scientifique (CNRS)

D. C. Lis

California Institute of Technology (Caltech)

E. A. Bergin

University of Michigan

J. C. Pearson

Jet Propulsion Laboratory, California Institute of Technology

M. de Luca

Centre national de la recherche scientifique (CNRS)

John H Black

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

Proceedings of the International Astronomical Union

1743-9213 (ISSN) 1743-9221 (eISSN)

Vol. 297 S297 197-202

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Roots

Basic sciences

Infrastructure

Onsala Space Observatory

DOI

10.1017/S1743921313015846

More information

Latest update

9/7/2018 1