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The OH-streamer in Sagittarius A revisited: Analysis of hydroxyl absorption within 10 pc from the Galactic centre
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, A118Article in journal (Refereed) Published
Abstract [en]

Aims. We study the structure and kinematics of the OH-streamer and the +80 km s(-1) cloud and their interactions with the circumnu-clear disk (CND) and with other molecular clouds in the vicinity of the Galactic centre (GC), and we map OH absorption at about 6 '' resolution at R <= 10 pc from the GC, with about 9 km s(-1) of velocity resolution. Methods. The VLA was used to map OH line absorption at the 1665 and 1667 MHz lambda doublet main lines of the (2)Pi(3/2) state towards the Sagittarius A complex. Results. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80 km s(-1) molecular clouds, the molecular belt, the CND, the expanding molecular ring (EMR), and the high negative velocity gas (HNVG). The OH-streamer was found to comprise three parts, head, mid, and tail, and to interact with the SS/+20, +80 km s(-1) clouds and the CND. Optical depths and column densities divided by excitation temperatures have been calculated for the OH-streamer and the +80 km s(-1) cloud. Conclusions. The OH-streamer, the SS, the +20 and +80 km s(-1) clouds, and the CND are intimately related in position and velocity space. The OH-streamer was found to be a clumpy object stretching in projection from the inner radius of the CND at about 1.8 pc from Sgr A*towards and partly engulfing Sgr A*. As a side result of our data, a possible link between the near side of the EMR and the CND's southwest lobe was found. Additionally, we found OH absorption against all four of the previously known compact H II regions A-D, located east of Sgr A East, indicating their close association with the +50 km s(-1) cloud.

Place, publisher, year, edition, pages
2015. Vol. 582, A118
Keyword [en]
Galaxy: center, ISM: individual objects: Sagittarius A, ISM: molecules, ISM: clouds
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-122687DOI: 10.1051/0004-6361/201424426ISI: 000363538500118OAI: oai:DiVA.org:su-122687DiVA: diva2:868107
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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