Odin observations of the Galactic centre in the 118-GHz band

Sandqvist, Aa.; Larsson, Bengt; Hjalmarson, Å.; Bergman, P.; Bernath, Peter F.; Frisk, U.; Olberg, M.; Pagani, L.; Ziurys, L. M.

doi:10.1051/0004-6361:200809436

Cited by 17 publications

(29 citation statements)

References 30 publications

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“…3), H 2 (Lee et al 2003(Lee et al , 2008, CH 3 OH (Stankovic et al 2007), HC 3 N (Sandqvist et al 2008), SiO (Amo-Baladrón et al 2009, etc., and also through dust submm continuum emission (e.g., Mezger et al 1989;Zylka et al 1990;Dent et al 1993;Lis & Carlstrom 1994). The early CO emission map of Solomon et al (1972) already revealed two massive molecular clouds peaking ≈3 east and ≈2.…”

Section: The Belt Of Molecular Cloudsmentioning

confidence: 99%

Interstellar gas within ~10 pc of Sagittarius A^∗

Ferrière

2012

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Aims. We seek to obtain a coherent and realistic three-dimensional picture of the interstellar gas out to about 10 pc of the dynamical center of our Galaxy, which is supposed to be at Sgr A * . Methods. We review the existing observational studies on the different gaseous components that have been identified near Sgr A * , and retain all the information relating to their spatial configuration and/or physical state. Based on the collected information, we propose a three-dimensional representation of the interstellar gas, which describes each component in terms of both its precise location and morphology and its thermodynamic properties. Results. The interstellar gas near Sgr A * can be represented by five basic components, which are, by order of increasing size: (1) a central cavity with roughly equal amounts of warm ionized and atomic gases; (2) a ring of mainly molecular gas; (3) a supernova remnant filled with hot ionized gas; (4) a radio halo of warm ionized gas and relativistic particles; and (5) a belt of massive molecular clouds. While the halo gas fills ≈80% of the studied volume, the molecular components enclose ≈98% of the interstellar mass.

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Section: The Belt Of Molecular Cloudsmentioning

confidence: 99%

Interstellar gas within ~10 pc of Sagittarius A^∗

Ferrière

2012

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“…Chemistry in post-shocked gas driven by neutral-neutral reactions has been invoked to reproduce HNCO abundances on the order of 10 −8 , as the high temperatures achieved by shocks could overcome the energy barriers of these reactions (for more details see Turner et al 1999;Tideswell et al 2010;Rodriguez-Fernandez et al 2010). However, this formation pathway presents two main drawbacks: the short times that shocks can maintain the required high temperatures and cannot detect O 2 in the Sgr A complex (X O 2 ≤ 1.2 × 10 −7 ; Sandqvist et al 2008), a key molecule in this formation path of HNCO.…”

Section: Hnco Chemistrymentioning

confidence: 99%

Mapping photodissociation and shocks in the vicinity of Sagittarius A^∗

Amo-Baladrón

Martı́n-Pintado

Martín

2010

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Aims. We study the chemistry in the harsh environments of galactic nuclei using the nearest one, the Galactic center (GC). Methods. We have obtained maps of the molecular emission within the central five arcminutes (12 pc) of the GC in selected molecular tracers: SiO(2-1), HNCO(5 0,5 -4 0,4 ), and the J = 1 → 0 transition of H 13 CO + , HN 13 C, and C 18 O at an angular resolution of 30 (1.2 pc). The mapped region includes the circumnuclear disk (CND) and the two surrounding giant molecular clouds (GMCs) of the Sgr A complex, known as the 20 and 50 km s −1 molecular clouds. Additionally, we simultaneously observed the J = 2 → 1 and J = 3 → 2 transitions of SiO toward selected positions to estimate the physical conditions of the molecular gas using the large velocity gradient approximation. Results. The SiO(2-1) emission shows all the molecular features identified in previous studies, covering the same velocity range as the H 13 CO + (1-0) emission, which also presents a similar distribution. In contrast, HNCO(5-4) emission appears in a narrow velocity range mostly concentrated in the 20 and 50 km s −1 GMCs. A similar trend follows the HN 13 C(1-0) emission. The HNCO column densities and fractional abundances present the highest contrast, with difference factors of ≥60 and 28, respectively. Their highest values are found toward the cores of the GMCs, whereas the lowest ones are measured at the CND. SiO abundances do not follow this trend, with high values found toward the CND, as well as the GMCs. By comparing our abundances with those of prototypical Galactic sources we conclude that HNCO, similar to SiO, is ejected from grain mantles into gas-phase by nondissociative C-shocks. This results in the high abundances measured toward the CND and the GMCs. However, the strong UV radiation from the Central cluster utterly photodissociates HNCO as we get closer to the center, whereas SiO seems to be more resistant against UV-photons or it is produced more efficiently by the strong shocks in the CND. This UV field could be also responsible for the trend found in the HN 13 C abundance. Conclusions. We discuss the possible connections between the molecular gas at the CND and the GMCs using the HNCO/SiO, SiO/CS, and HNCO/CS intensity ratios as probes of distance to the Central cluster. In particular, the HNCO/SiO intensity ratio is proved to be an excellent tool for evaluating the distance to the center of the different gas components.

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“…Quan et al (2008, and references therein) present a recent overview for our understanding of the abundance of interstellar molecular oxygen. In general, the amount of O 2 in molecular clouds has been below detection capability of the dedicated space missions SWAS (e.g., Goldsmith et al 2000;Bergin et al 2000) and Odin (e.g., Pagani et al 2003;Sandqvist et al 2008). In merely one single location, viz.…”

Section: Introductionmentioning

confidence: 99%

Oxygen in dense interstellar gas

Liseau

Justtanont

2009

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Context. Oxygen is the third most abundant element in the universe, but its chemistry in the interstellar medium is still not understood well. Aims. To critically examine the entire oxygen budget, we initially attempt to estimate the abundance of atomic oxygen, O, in the only region where molecular oxygen, O 2 , has been detected to date. Methods. We analysed ISOCAM-CVF spectral image data toward ρ Oph A to derive the temperatures and column densities of H 2 at the locations of ISO-LWS observations of two [O I] 3 P J lines. The intensity ratios of the (J = 1-2) 63 μm to (J = 0-1) 145 μm lines largely exceed ten, attesting to these lines being optically thin. This is confirmed by radiative transfer calculations, making these lines suitable for abundance determinations. For that purpose, we calculated line strengths and compared them to the LWS observations. Results. Excess [O I] emission is observed to be associated with the molecular outflow from VLA 1623. For this region, we determine the physical parameters, T and N(H 2 ), from the CAM observations, and the gas density, n(H 2 ), is determined from the flux ratio of Conclusions. As option (1) disregards valid [O i] 145 μm data, we do not find it very compelling; instead, we favour option (3), as lower abundances are expected as a result of chemical cloud evolution, but we are not able to dismiss option (2) entirely. Observations at higher angular resolution than offered by the LWS are required to decide between these possibilities.

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Odin observations of the Galactic centre in the 118-GHz band

Abstract: Aims. The Odin satellite has been used to search for the 118.75-GHz line of molecular oxygen (O 2 ) in the Galactic centre. Methods. Odin observations were performed towards the Sgr A * circumnuclear disk (CND), and the Sgr A +20 km s −1 and +50 km s

Cited by 17 publications

References 30 publications

Interstellar gas within ~10 pc of Sagittarius A^∗

Interstellar gas within ~10 pc of Sagittarius A^∗

Mapping photodissociation and shocks in the vicinity of Sagittarius A^∗

Oxygen in dense interstellar gas

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Odin observations of the Galactic centre in the 118-GHz band

Abstract: Aims. The Odin satellite has been used to search for the 118.75-GHz line of molecular oxygen (O 2 ) in the Galactic centre. Methods. Odin observations were performed towards the Sgr A * circumnuclear disk (CND), and the Sgr A +20 km s −1 and +50 km s

Cited by 17 publications

References 30 publications

Interstellar gas within ~10 pc of Sagittarius A∗

Interstellar gas within ~10 pc of Sagittarius A∗

Mapping photodissociation and shocks in the vicinity of Sagittarius A∗

Oxygen in dense interstellar gas

Contact Info

Product

Resources

About

Interstellar gas within ~10 pc of Sagittarius A^∗

Interstellar gas within ~10 pc of Sagittarius A^∗

Mapping photodissociation and shocks in the vicinity of Sagittarius A^∗