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| 2. |
- Karlsson, Roland, 1948-, et al.
(författare)
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18-cm VLA observations of OH towards the Galactic Centre : Absorption and emission in the four ground-state OH lines
- 2003
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 403, s. 1011-1021
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Karlsson, Roland, 1948-, et al.
(författare)
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Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex
- 2014
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 9:303, s. 97-99
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Tidskriftsartikel (refereegranskat)abstract
- We observed Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the +50 km s−1 cloud (M−0.02−0.07), the circumnuclear disk (CND) and the +20 km s−1 (M−0.13−0.08) cloud in the Sgr A complex with the VLA, Odin and SEST. Strong OH absorption, H2O emission and absorption lines were seen at all three positions. Strong C18O emissions were seen towards the +50 and +20 km s−1 clouds. The CND is rich in H2O and OH, and these abundances are considerably higher than in the surrounding clouds, indicating that shocks, star formation and clump collisions prevail in those objects. A comparison with the literature reveals that it is likely that PDR chemistry including grain surface reactions, and perhaps also the influences of shocks has led to the observed abundances of the observed molecular species studied here. In the redward high-velocity line wings of both the +50 and +20 km s−1 clouds and the CND, the very high H2O abundances are suggested to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry. Only three of the molecules are briefly discussed here. For OH and H2O three of the nine observed positions are shown, while a map of the C18O emission is provided. An extensive paper was recently published with Open Access (Karlsson et al. 2013, A&A 554, A141).
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| 5. |
- Karlsson, Roland, 1948-
(författare)
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Studies of molecular clouds at the Galactic centre
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Karlsson, Roland, 1948-, et al.
(författare)
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The 18 cm OH distribution in the Galactic Center Torus
- 1987
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Ingår i: AIP Conference Proceedings. - New York : American Institute of Physics (AIP). - 0094-243X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The 18‐cm OH distribution in the Galactic Center region near Sgr A has been studied in all four of the 1612, 1665, 1667 and 1720 MHz OH lines using the VLA with 4 arcsec angular resolution and 9 km s− 1 velocity resolution. Three 1667 MHz OH spectral line absorption maps, at +51, +25 and −1 km s− 1, covering a 4’.3×4’.3 region around Sgr A are presented together with an 18‐cm continuum map. In addition, a complete set of velocity maps from +139 to −159 km s− 1, covering a 3’×3’ region around the Galactic Center nuclear torus, is presented. Absorption by the +50 and +20 km s− 1 molecular cloud belt is seen towards Sgr A East, but not towards Sgr A West. Absorption is also seen towards Sgr A* in the velocity ranges of +43 to −36 km s− 1 and −142 to −151 km s− 1. The Northeast and Southwest torus components can be traced out to velocities of +139 and −151 km s− 1. A ‘‘Northwest’’ feature, starting northwest of the Western continuum arc, appears faintly at a velocity of +51 km s− 1 and then migrates slightly southward until it merges with another feature at a velocity of +78 km s− 1. This other feature ‘‘Sweeps’’ in towards Sgr A* as the velocity decreases from +78 to +16 km s− 1.
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| 7. |
- Karlsson, Roland, 1948-, et al.
(författare)
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The OH-streamer in Sagittarius A revisited : Analysis of hydroxyl absorption within 10 pc from the Galactic centre
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 582
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Karlsson, Roland, 1948-, et al.
(författare)
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VizieR Online Data Catalog : OH-streamer in SgrA at 1665 and 1667MHz (Karlsson+, 2015)
- 2015
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The VLA was used to map OH line absorption at the 1665 and 1667MHz lambda doublet main lines of the 2{Pi}3/2 state towards the Sagittarius A complex. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80km/s molecular clouds, the molecular belt, the CND, the expanding molecular ring (EMR), and the high negative velocity gas (HNVG).Data cubes of VLA observations of the Sgr A complex at 1667- and 1665MHz OH-absorption at 7"x5" angular and 8.8km/s velocity resolution in 63 spectral channels centered at -38km/s (LSR). OH-absorption is defined as "continuum flux minus line flux". The continuum is taken as the average of 1665 and 1667 MHz maps of line free channels. Observations with the VLA in BnA and DnC arrays have been concatenated with AIPS, and data were calibrated and CLEANed with NRAO AIPS standard procedures.(2 data files).
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| 9. |
- Sandqvist, Aage, 1939-, et al.
(författare)
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OH in the environment of Sgr A
- 1989
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Ingår i: The center of the GalaxyThe Center of the Galaxy: Proceedings of the 136th Symposium of the International Astronomical Union, held in Los Angeles, U.S.A. - : Kluwer Academic Publishers. ; , s. 421-422
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 10. |
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