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Sandqvist, Aage
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Publications (10 of 42) Show all publications
Sandqvist, A., Hjalmarson, Å., Larsson, B., Frisk, U., Lundin, S. & Rydbeck, G. (2021). Herschel and Odin observations of H2O, CO, CH, CH+, and [NII] in the barred spiral galaxy NGC 1365 Bar-induced activity in the outer and inner circumnuclear tori. Astronomy and Astrophysics, 647, Article ID A86.
Open this publication in new window or tab >>Herschel and Odin observations of H2O, CO, CH, CH+, and [NII] in the barred spiral galaxy NGC 1365 Bar-induced activity in the outer and inner circumnuclear tori
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2021 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 647, article id A86Article in journal (Refereed) Published
Abstract [en]

Context. The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major astronomical pursuits was the search for and study of water vapor in diverse regions of the Solar System and the Milky Way galaxy. The Herschel space observatory was needed to detect water vapor in external galaxies.

Aims. Our goal is to study the distribution and excitation of water vapor and other molecules in the barred spiral galaxy NGC 1365.

Methods. Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 mu m infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 mu m images. The Herschel SPIRE observations have been used to produce simultaneously observed maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6-5), 1037 GHz CO(9-8), 537 GHz CH, 835 GHz CH', and the 1461 GHz [N IT] lines (efficiently probing the warm ionized medium) in the inner bar and circumnuclear torus region; - however, these observations have no effective velocity resolution. For this reason Odin has recently observed the 557 GHz ortho-H2O ground state line in the central region with high (5 km s(-1)) spectral resolution.

Results. The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km s(-1), has been marginally detected in NGC 1365 with Odin. The water vapor is predominantly located in a shocked 15 '' (1.3 kpc) region near some central compact radio sources and hot-spot HIT regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3-2) observations, yielding 5 '' resolution, and a study of our Very Large Array HI absorption observations, as well as comparisons with published interferometric CO observations. Additionally, an enticing 20 '' HI ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an O III outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region of NGC 1365 is analyzed with special emphasis on the CO, H2O and CH, CH+ results.

Conclusions. The dominating activity near the northeast (NE) torus component may have been triggered by the rapid bar-driven inflow into the circumnuclear torus causing cloud-cloud collisions and shocks, leading to the formation of stellar superclusters and, hence, also to more efficient PDR chemistry, which, here, may also benefit from cosmic ray focusing caused by the observed aligned magnetic field. The very high activity near the NE torus component may reflect the fact that the eastern bar-driven gas inflow into the NE region is much more massive than the corresponding western gas inflow into the southwest region. The H2O and CH+ emissions peak in the NE torus region, but the CO and CH emissions are more evenly distributed across the whole circumnuclear torus. The higher energy CO spectral line energy distribution (SLED) is nicely modeled by a low velocity (10 km s(-1)) shock, which may as well explain the required CH excitation and its high abundance in denser gas. The higher velocity (40 km s(-1)) shock required to model the H2O SLED in the NE torus region, paired with the intense UV radiation from the observed massive young stellar superclusters, may also explain the high abundance of CH+ in this region. The nuclear H I ridge may have been created by the action of outflow-driving X-ray photons colliding with ice-covered dust grains. A precessing nuclear engine, as is suggested by the tilted massive inner gas torus, may be necessary to explain the various nuclear outflows encountered.

Keywords
galaxies: ISM, galaxies: individual: NGC 1365, galaxies: Seyfert, galaxies: nuclei
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-193217 (URN)10.1051/0004-6361/202038875 (DOI)000629650600001 ()
Available from: 2021-05-18 Created: 2021-05-18 Last updated: 2022-02-25Bibliographically approved
Benmahi, B., Cavali, T., Dobrijevic, M., Biver, N., Bermudez-Diaz, K., Sandqvist, A., . . . Olberg, M. (2020). Monitoring of the evolution of H2O vapor in the stratosphere of Jupiter over an 18-yr period with the Odin space telescope. Astronomy and Astrophysics, 641, Article ID A140.
Open this publication in new window or tab >>Monitoring of the evolution of H2O vapor in the stratosphere of Jupiter over an 18-yr period with the Odin space telescope
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2020 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 641, article id A140Article in journal (Refereed) Published
Abstract [en]

Context. The comet Shoemaker-Levy 9 impacted Jupiter in July 1994, leaving its stratosphere with several new species, with water vapor (H2O) among them.

Aims. With the aid of a photochemical model, H2O can be used as a dynamical tracer in the Jovian stratosphere. In this paper, we aim to constrain the vertical eddy diffusion (Kzz) at levels where H2O is present.

Methods. We monitored the H2O disk-averaged emission at 556.936 GHz with the space telescope between 2002 and 2019, covering nearly two decades. We analyzed the data with a combination of 1D photochemical and radiative transfer models to constrain the vertical eddy diffusion in the stratosphere of Jupiter. Results. Odin observations show us that the emission of H2O has an almost linear decrease of about 40% between 2002 and 2019. We can only reproduce our time series if we increase the magnitude of Kzz in the pressure range where H2O diffuses downward from 2002 to 2019, that is, from ~0.2 mbar to ~5 mbar. However, this modified Kzz is incompatible with hydrocarbon observations. We find that even if an allowance is made for the initially large abundances of H2O and CO at the impact latitudes, the photochemical conversion of H2O to CO2 is not sufficient to explain the progressive decline of the H2O line emission, which is suggestive of additional loss mechanisms.

Conclusions. The Kzz we derived from the Odin observations of H2O can only be viewed as an upper limit in the ~0.2 mbar to ~5 mbar pressure range. The incompatibility between the interpretations made from H2O and hydrocarbon observations probably results from 1D modeling limitations. Meridional variability of H2O, most probably at auroral latitudes, would need to be assessed and compared with that of hydrocarbons to quantify the role of auroral chemistry in the temporal evolution of the H2O abundance since the SL9 impacts. Modeling the temporal evolution of SL9 species with a 2D model would naturally be the next step in this area of study.

Keywords
planets and satellites: individual: Jupiter, planets and satellites: atmospheres, submillimeter: planetary systems
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-187314 (URN)10.1051/0004-6361/202038188 (DOI)000576407600001 ()
Available from: 2020-12-15 Created: 2020-12-15 Last updated: 2022-02-25Bibliographically approved
Sandqvist, A., Hjalmarson, A., Frisk, U., Lundin, S., Nordh, L., Olberg, M. & Olofsson, G. (2017). Odin observations of ammonia in the SgrA+50 km s(-1) cloud and circumnuclear disk. Astronomy and Astrophysics, 599, Article ID A135.
Open this publication in new window or tab >>Odin observations of ammonia in the SgrA+50 km s(-1) cloud and circumnuclear disk
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 599, article id A135Article in journal (Refereed) Published
Abstract [en]

Context. The Odin satellite is now into its sixteenth year of operation, much surpassing its design life of two years. One of the sources which Odin has observed in great detail is the Sgr A complex in the centre of the Milky Way.

Aims. To study the presence of NH3 in the Galactic centre and spiral arms.

Methods. Recently, Odin has made complementary observations of the 572 GHz NH3 line towards the SgrA + 50 km s(-1) cloud and circumnuclear disk (CND).

Results. Significant NH3 emission has been observed in both the + 50 km s(-1) cloud and the CND. Clear NH3 absorption has also been detected in many of the spiral arm features along the line of sight from the Sun to the core of our Galaxy.

Conclusions. The very large velocity width (80 km s 1) of the NH3 emission associated with the shock region in the southwestern part of the CND may suggest a formation / desorption scenario similar to that of gas-phase H2O in shocks / outflows.

Keywords
Galaxy: center, ISM: individual objects: Sgr A, ISM: molecules, ISM: clouds
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-148922 (URN)10.1051/0004-6361/201629954 (DOI)000413691400015 ()
Available from: 2017-11-13 Created: 2017-11-13 Last updated: 2022-02-28Bibliographically approved
Biver, N., Moreno, R., Bockelée-Morvan, D., Sandqvist, A., Colom, P., Crovisier, J., . . . Murtagh, D. (2016). Isotopic ratios of H, C, N, O, and S in comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy). Astronomy and Astrophysics, 589, Article ID A78.
Open this publication in new window or tab >>Isotopic ratios of H, C, N, O, and S in comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy)
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 589, article id A78Article in journal (Refereed) Published
Abstract [en]

The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in March-April 2013 and January 2015, combined with the improved observational capabilities of submillimeter facilities, offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. We observed comet Lovejoy with the IRAM 30 m telescope between 13 and 26 January 2015, and with the Odin submillimeter space observatory on 29 January-3 February 2015. We detected 22 molecules and several isotopologues. The (H2O)-O-16 and (H2O)-O-18 production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of similar to 25%. The inferred isotope ratios in comet Lovejoy are O-16/O-18 = 499 +/- 24 and D/H = 1.4 +/- 0.4 x 10(-4) in water, S-32/S-34 = 24.7 +/- 3.5 in CS, all compatible with terrestrial values. The ratio C-12/C-13 = 109 +/- 14 in HCN is marginally higher than terrestrial and N-14/N-15 = 145 +/- 12 in HCN is half the Earth ratio. Several upper limits for D/H or C-12/C-13 in other molecules are reported. From our observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value. On the other hand, the observation of the same HDO line in the other Oort-cloud comet, C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous measurements of D/H in cometary water, this illustrates that a diversity in the D/H ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system.

Keywords
radio lines: planetary systems, submillimeter: planetary systems, comets: individual: C/2012 F6 (Lemmon), comets: individual: C/2014 Q2 (Lovejoy), comets: general
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-168085 (URN)10.1051/0004-6361/201528041 (DOI)000375318300090 ()
Available from: 2019-04-24 Created: 2019-04-24 Last updated: 2022-02-26Bibliographically approved
Biver, N., Bockelée-Morvan, D., Moreno, R., Crovisier, J., Colom, P., Lis, D. C., . . . Milam, S. N. (2015). Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy). Science Advances, 1(9), Article ID e1500863.
Open this publication in new window or tab >>Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy)
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2015 (English)In: Science Advances, E-ISSN 2375-2548, Vol. 1, no 9, article id e1500863Article in journal (Refereed) Published
Abstract [en]

The presence of numerous complex organic molecules (COMs; defined as those containing six or more atoms) around protostars shows that star formation is accompanied by an increase of molecular complexity. These COMs may be part of the material from which planetesimals and, ultimately, planets formed. Comets represent some of the oldest and most primitive material in the solar system, including ices, and are thus our best window into the volatile composition of the solar protoplanetary disk. Molecules identified to be present in cometary ices include water, simple hydrocarbons, oxygen, sulfur, and nitrogen-bearing species, as well as a few COMs, such as ethylene glycol and glycine. We report the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first identification of ethyl alcohol (ethanol, C2H5OH) and the simplest monosaccharide sugar glycolaldehyde (CH2OHCHO) in a comet. The abundances of ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12 and 0.02% relative to water), are somewhat higher than the values measured in solar-type protostars. Overall, the high abundance of COMs in cometary ices supports the formation through grain-surface reactions in the solar system protoplanetary disk.

National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-122498 (URN)10.1126/sciadv.1500863 (DOI)000216598200036 ()
Available from: 2015-11-03 Created: 2015-11-03 Last updated: 2022-02-23Bibliographically approved
Sandqvist, A., Larsson, B., Hjalmarson, Å., Encrenaz, P., Gerin, M., Goldsmith, P. F., . . . Viti, S. (2015). Herschel HIFI observations of the Sgr A+50 km s(-1) Cloud Deep searches for O-2 in emission and foreground absorption. Astronomy and Astrophysics, 584, Article ID A118.
Open this publication in new window or tab >>Herschel HIFI observations of the Sgr A+50 km s(-1) Cloud Deep searches for O-2 in emission and foreground absorption
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2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 584, article id A118Article in journal (Refereed) Published
Abstract [en]

Context: The Herschel Oxygen Project (HOP) is an open time key program, awarded 140 h of observing time to search for molecular oxygen (O-2) in a number of interstellar sources. To date O-2 has definitely been detected in only two sources, namely rho Oph A and Orion, reflecting the extremely low abundance of O-2 in the interstellar medium.

Aims: One of the sources in the HOP program is the + 50 km s(-1) Cloud in the Sgr A Complex in the centre of the Milky Way. Its environment is unique in the Galaxy and this property is investigated to see if it is conducive to the presence of O-2. Methods. The Herschel Heterodyne Instrument for the Far Infrared (HIFI) is used to search for the 487 and 774 GHz emission lines of O-2.

Results: No O-2 emission is detected towards the Sgr A + 50 km s(-1) Cloud, but a number of strong emission lines of methanol (CH3OH) and absorption lines of chloronium (H2Cl+) are observed.

Conclusions: A 3 sigma upper limit for the fractional abundance ratio of [O-2]/[H-2] in the Sgr A + 50 km s(-1) Cloud is found to be X(O-2) <= 5x 10(-8). However, since we can find no other realistic molecular candidate than O-2 itself, we very tentatively suggest that two weak absorption lines at 487.261 and 487.302 GHz may be caused by the 487 GHz line of O-2 in two foreground spiral arm clouds. By considering that the absorption may only be apparent, the estimated upper limit to the O-2 abundance of <=(10-20) x 10(-6) in these foreground clouds is very high, as opposed to the upper limit in the Sgr A + 50 km s(-1) Cloud itself, but similar to what has been reached in recent chemical shock models for Orion. This abundance limit was determined also using Odin non-detection limits, and assumes that O-2 fills the beam. If the absorption is due to a differential Herschel OFF-ON emission, the O-2 fractional abundance may be of the order of approximate to(5-10) x 10 (6). With the assumption of pure absorption by foreground clouds, the unreasonably high abundance of (1.4-2.8) x 10(-4) was obtained. The rotation temperatures for CH3OH-A and CH3OH-E lines in the + 50 km s(-1) Cloud are found to be approximate to 64 and 79 K, respectively, and the fractional abundance of CH3OH is approximately 5 x 10(-7).

Keywords
Galaxy: center, ISM: individual objects: Sgr A, ISM: molecules, ISM: clouds
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-125784 (URN)10.1051/0004-6361/201526280 (DOI)000366936800118 ()
Available from: 2016-01-27 Created: 2016-01-18 Last updated: 2022-02-23Bibliographically approved
Karlsson, R., Sandqvist, A., Fathi, K. & Martin, S. (2015). The OH-streamer in Sagittarius A revisited: Analysis of hydroxyl absorption within 10 pc from the Galactic centre. Astronomy and Astrophysics, 582, Article ID A118.
Open this publication in new window or tab >>The OH-streamer in Sagittarius A revisited: Analysis of hydroxyl absorption within 10 pc from the Galactic centre
2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, article id 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.

Keywords
Galaxy: center, ISM: individual objects: Sagittarius A, ISM: molecules, ISM: clouds
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-122687 (URN)10.1051/0004-6361/201424426 (DOI)000363538500118 ()
Available from: 2015-11-09 Created: 2015-11-09 Last updated: 2022-03-23Bibliographically approved
Karlsson, R., Sandqvist, A., Fathi, K. & Martin, S. (2015). VizieR Online Data Catalog: OH-streamer in SgrA at 1665 and 1667MHz (Karlsson+, 2015). Smithsonian Astrophysical Observatory (SAO)
Open this publication in new window or tab >>VizieR Online Data Catalog: OH-streamer in SgrA at 1665 and 1667MHz (Karlsson+, 2015)
2015 (English)Other (Other academic)
Abstract [en]

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).

Place, publisher, year, pages
Smithsonian Astrophysical Observatory (SAO), 2015
Keywords
Milky Way, Interstellar medium, Molecular clouds
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-126753 (URN)
Note

Originally published in: Astronomy & Astrophysics, Volume 582, id. A118. 10/2015.

Available from: 2016-02-15 Created: 2016-02-15 Last updated: 2022-02-23Bibliographically approved
Karlsson, R., Sandqvist, A., Hjalmarson, Å., Winnberg, A., Fathi, K., Frisk, U. & Olberg, M. (2014). Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex. Paper presented at 303rd Symposium of the International-Astronomical-Union, Santa Fe, New Mexico, September 30 - October 4, 2013. Proceedings of the International Astronomical Union, 9(303), 97-99
Open this publication in new window or tab >>Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex
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2014 (English)In: Proceedings of the International Astronomical Union, ISSN 1743-9213, E-ISSN 1743-9221, Vol. 9, no 303, p. 97-99Article in journal (Refereed) Published
Abstract [en]

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).

Keywords
Sgr A, +50, +20 km s−1clouds, CND, OH, H2O abundances, gas-phase chemistry
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-122688 (URN)10.1017/S174392131400026X (DOI)000450812600018 ()
Conference
303rd Symposium of the International-Astronomical-Union, Santa Fe, New Mexico, September 30 - October 4, 2013
Available from: 2015-11-09 Created: 2015-11-09 Last updated: 2022-02-23Bibliographically approved
Karlsson, R., Sandqvist, A., Hjalmarson, A., Winnberg, A., Fathi, K., Frisk, U. & Olberg, M. (2013). Hydroxyl, water, ammonia, carbon monoxide, and neutral carbon towards the Sagittarius A complex VLA, Odin, and SEST observations. Astronomy and Astrophysics, 554, Article ID A141.
Open this publication in new window or tab >>Hydroxyl, water, ammonia, carbon monoxide, and neutral carbon towards the Sagittarius A complex VLA, Odin, and SEST observations
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2013 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 554, article id A141Article in journal (Refereed) Published
Abstract [en]

Aims. The Sagittarius A complex in the Galactic centre comprises an ensemble of molecular clouds of different species with a variety of geometrical and kinematic properties. This work aims to study molecular abundances, morphology, and kinematics by comparing hydroxyl, water, carbon monoxide, ammonia, and atomic carbon and some of their isotopologues, in the +50 km s(-1) cloud, the circumnuclear disk (CND), the +20 km s(-1) cloud, the expanding molecular ring and the line-of-sight spiral arm features, including the Local/Sgr arm, the -30 km s(-1) arm, and the 3-kpc arm. Methods. We observed the +50 km s(-1) cloud, the CND and the +20 km s(-1) cloud, and other selected positions at the Galactic centre with the VLA, and the Odin satellite. The VLA was used to map the 1665 and 1667 MHz OH lambda doublet main lines of the (H-2(3/2)) state, and the Odin satellite was used to map the 557 GHz H2O (1(10)-1(01)) line as well as to observe the 548 GHz (H2O)-O-18 (1(10)-1(01)) line, the 572 GHz NH3 (1(0)-0(0)) line, the 576 GHz CO J = 5-4 line and the 492 GHz C-I (P-3(1)-P-3(0)) line. Furthermore, the SEST was used to map a 4'.5 x 6' region of the SgrAcomplex in the 220 GHz (CO)-O-18 J = 2-1 line. Results. Strong OH absorption, H2O emission and absorption lines were seen at all observed positions, and the (H2O)-O-18 line was detected in absorption towards the +50 km s(-1) cloud, the CND, the +20 km s(-1)cloud, the expanding molecular ring, and the 3-kpc arm. Strong CO J = 5-4, (CO)-O-18 J = 2-1, and neutral carbon C-I emissions were seen towards the +50 and +20 km s(-1) clouds. NH3 was only detected in weak absorption originating in the line-of-sight spiral arm features. The abundances of OH and H2O in the +50 and +20 km s(-1) clouds reflect the different physical environments in the clouds, where shocks and star formation prevail in the +50 km s(-1) cloud and giving rise to a higher rate of H2O production there than in the +20 km s(-1) cloud. In the CND, cloud collisions and shocks are frequent, and the CND is also subject to intense UV-radiation emanating from the supermassive black hole and the central star cluster. The CND is rich in (HO)-O-2 and OH, and these abundances are considerably higher than in the +50 and +20 km s(-1) clouds. We compare our estimated abundances of OH, H2O, and NH3 with similar and differing results for some other sources available in the literature. As compared to the quiescent cloud values of a few x 10(-9), or lower, the H2O abundance is markedly enhanced in the front sides of the Sgr A molecular cloud cores, (2-7) x 10(-8), as observed in absorption, and highest in the CND. A similar abundance enhancement is seen in OH. The likely explanation is PDR chemistry including grain surface reactions, and perhaps also the influence of shocks. In the redward high-velocity line wings of the +50 and +20 km s(-1) clouds and the CND, the H2O abundances are estimated to be (1-6) x 10(-6) or higher, i.e., similar to the water abundances in outflows of the Orion KL and DR21 molecular clouds, which are said to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry.

Keywords
Galaxy: center, ISM: clouds, ISM: molecules, Galaxy: abundances
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-92660 (URN)10.1051/0004-6361/201220471 (DOI)000320444200139 ()
Note

AuthorCount:7;

Available from: 2013-08-14 Created: 2013-08-14 Last updated: 2022-02-24Bibliographically approved
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