Ph D Thesis: Studies of molecular clouds at the Galactic centre
by
Roland Karlsson(Stockholm University, Dept. of Astronomy)
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Europe/Stockholm
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Description
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.
