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18-cm VLA observations of OH towards the Galactic Centre: Absorption and emission in the four ground-state OH lines
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
2003 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 403, 1011-1021 p.Article in journal (Refereed) Published
Abstract [en]

The OH distribution in the Sgr A Complex has been observed in the 1612-, 1665-, 1667- and 1720-MHz OH transitions with the Very Large Array (VLA) in BnA configuration. Maps are presented with a channel velocity resolution of about 9 km s -1 and with angular resolutions of  . Some clear results are highlighted here, such as absorption from the Circumnuclear Disk (CND) and the OH-Streamer inside the CND near Sgr , strong absorption towards most of the eastern and western parts of the Sgr A East shell, lack of absorption towards both Sgr A West and the compact H II-regions to the east of Sgr A East, and double-lobed structure of the High Negative Velocity Gas (HNVG) oriented northeast and southwest of Sgr , and finally compact, point-like maser emission in all four transitions, in particular a 1720-MHz maser at -132 km s -1 in the CND as counterpart to a 1720-MHz maser at +132 km s -1 in the CND.

Place, publisher, year, edition, pages
2003. Vol. 403, 1011-1021 p.
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-122685DOI: 10.1051/0004-6361:20030309OAI: oai:DiVA.org:su-122685DiVA: diva2:868097
Available from: 2015-11-09 Created: 2015-11-09 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Studies of molecular clouds at the Galactic centre
Open this publication in new window or tab >>Studies of molecular clouds at the Galactic centre
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Interstellar molecular clouds play an essential role in the Universe. Such clouds are invoked for the production and destruction of stars, galaxies and gas and also for energy transport in galaxies. The Galaxy, or the Milky Way, is a large spiral galaxy, with a central bar structure, that harbours a few hundred billion stars and large amounts of gas and dust. At the centre of the Galaxy, a 4 million solar mass supermassive black hole resides, surrounded by a dense core of millions of stars, as well as molecular and dust clouds. The Galactic centre (GC) is hidden by gas and dust, such that only astronomical observations of radio-, infrared-, X-rays and gamma-rays are available for a gathering of information at the centre. In this work, I have studied neutral molecular clouds in absorption at the innermost 50 light years from the centre with the Karl Jansky Very Large Array Observatory in New Mexico in the USA, and with data from observations with the Swedish-ESO Submillimetre Telescope in Chile, and also from the orbital observatory Odin. I have detected a new stream-like feature of gas that seems to link a previously known ring of gas clouds (the CND) and the GC. Moreover, the hypothesis of feeding the CND from an outside cloud is supported by this work. Contemporary discussions in the literature that the central bar structure would act as a pump of material inwards from the spiral arms towards the GC via molecular clouds are also suggested by the data. A number of maser sources have been observed and some of those are shown to reside at shock fronts or anticipated regions of collisions between molecular clouds or at star forming regions. Unusually high water abundance was detected at the south-west part of the CND, indicative of shocks and strong turbulence. Moreover, I have produced high-resolution spectral line maps of hydroxyl (OH) absorption intensity in the four main transition lines of OH at 1612, 1720, 1665 and 1667 MHz, as well as apparent opacity and position-velocity maps of the GC region.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2016
Keyword
Galactic centre
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-126752 (URN)978-91-7649-356-4 (ISBN)
Public defence
2016-04-29, The Svedbergsalen (FD5), AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2016-04-06 Created: 2016-02-15 Last updated: 2017-02-20Bibliographically approved

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