New Detections of Galactic Molecular Absorption Systems toward ALMA Calibrator Sources

Abstract

We report on Atacama Large Millimeter/submillimeter Array (ALMA) detections of molecular absorption lines in Bands 3, 6 and 7 toward four radio-loud quasars, which were observed as the bandpass and complex gain calibrators. The absorption systems, three of which are newly detected, are found to be Galactic origin. Moreover, HCO absorption lines toward two objects are detected, which almost doubles the number of HCO absorption samples in the Galactic diffuse medium. In addition, high HCO to H13CO+ column density ratios are found, suggesting that the interstellar media (ISM) observed toward the two calibrators are in photodissociation regions, which observationally illustrates the chemistry of diffuse ISM driven by ultraviolet (UV) radiation. These results demonstrate that calibrators in the ALMA Archive are potential sources for the quest for new absorption systems and for detailed investigation of the nature of the ISM.

10 pages, 5 figures, accepted for publication in PASJ

References in corpus (6)

• [CII] absorption and emission in the diffuse interstellar medium across the Galactic Plane
• HCO mapping of the Horsehead : Tracing the illuminated dense molecular cloud surfaces
• An ALMA Early Science survey of molecular absorption lines toward PKS1830-211 -- Analysis of the absorption profiles
• HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds
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• Molecular absorptions in high-z objects

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• Molecular Gas and Dark Neutral Medium in the Outskirts of Chamaeleon
• The diffuse molecular component in the nuclear bulge of the Milky Way
• The peculiar chemistry of the inner ejecta of Eta Carina
• ALMA observations of molecular absorption in four directions toward the Galactic bulge
• Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance