270 pc Expanding Ring at the Galactic Centre

Kaifu, Norio; Kato, T.; Iguchi, Tetsuo

doi:10.1038/physci238105a0

Cited by 74 publications

(81 citation statements)

References 8 publications

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“…Approximately half of the latter (1.6 ϫ 10 15 cm Ϫ2 ) is in clouds with velocities near Ϫ100 km s Ϫ1 ; their average temperature is (270 Ϯ 70) K, and the density is lower than 50 cm Ϫ3 , although uncertainty of the latter may be high because of uncertainty of the collision cross section (a factor of 2). The large negative velocity suggests strongly that these clouds are associated with the large-scale structure moving away from the Galactic center at high speed initially proposed as the Expanding Molecular Ring (EMR) (58,59). It exists at Ϸ180 pc from the center, at about the border of the CMZ.…”

Section: Warm and Diffuse Clouds In The Cmzmentioning

confidence: 99%

Interstellar H ₃ ⁺

Oka¹

2006

Proc. Natl. Acad. Sci. U.S.A.

157

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Protonated molecular hydrogen, H 3؉ , is the simplest polyatomic molecule. It is the most abundantly produced interstellar molecule, next only to H2, although its steady state concentration is low because of its extremely high chemical reactivity. H 3 ؉ is a strong acid (proton donor) and initiates chains of ion-molecule reactions in interstellar space thus leading to formation of complex molecules. Here, I summarize the understandings on this fundamental species in interstellar space obtained from our infrared observations since its discovery in 1996 and discuss the recent observations and analyses of H 3 ؉ in the Central Molecular Zone near the Galatic center that led to a revelation of a vast amount of warm and diffuse gas existing in the region.

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Section: Warm and Diffuse Clouds In The Cmzmentioning

confidence: 99%

Interstellar H ₃ ⁺

Oka¹

2006

Proc. Natl. Acad. Sci. U.S.A.

157

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“…3.1.2 THE EMR VERSUS THE BAR Perceived in early molecular data as an ellipse in the l-v plane, the 180-pc molecular ring was originally interpreted as a radially expanding molecular ring surrounding the Galactic center (Scoville 1972, Kaifu et al 1972 and was subsequently referred to as the EMR. It was hypothesized to be the result of an explosive event at the center ∼ 10 6 years ago, which gave a radial momentum impulse to ∼ 10 7 M of nearby gas (Bania 1977).…”

Section: Response Of Interstellar Gas To a Bar Potentialmentioning

confidence: 99%

The Galactic Center Environment

Morris

Serabyn

1996

Annu. Rev. Astron. Astrophys.

899

905

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The central half kiloparsec region of our Galaxy harbors a variety of phenomena unique to the central environment. This review discusses the observed structure and activity of the interstellar medium in this region in terms of its inevitable inflow toward the center of the Galactic gravitational potential well. A number of dissipative processes lead to a strong concentration of gas into a "Central Molecular Zone" of about 200-pc radius, in which the molecular medium is characterized by large densities, large velocity dispersions, high temperatures, and apparently strong magnetic fields. The physical state of the gas and the resultant star formation processes occurring in this environment are therefore quite unlike those occurring in the large-scale disk. Gas not consumed by star formation either enters a hot X ray-emitting halo and is lost as a thermally driven galactic wind or continues moving inward, probably discontinuously, through the domain of the few parsec-sized circumnuclear disks and eventually into the central parsec. There, the central radio source SgrA * currently accepts only a tiny fraction of the inflowing material, likely as a result of a limit cycle wherein the continual inflow of matter provokes star formation, which in turn can temporarily halt the inflow via mass-outflow winds.

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“…Molecular gas at velocities < −100 km s −1 and > 120 km s −1 is usually attributed to the expanding molecular ring (EMR; Kaifu et al 1972Kaifu et al , 1974Scoville 1972) around the Galactic center. Given its position, G1.6−0.025 is at the high longitude end of that ring.…”

Section: Molecular Line Datamentioning

confidence: 99%

Molecules in G1.6–0.025—“HOT” Chemistry in the Absence of Star Formation at the Periphery of the Galactic Center Region

Menten

Wilson

Leurini

et al. 2009

ApJ

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We present molecular line mapping of the Giant Molecular Cloud G1.6−0.025, which is located at the highlongitude end of the Central Molecular Zone (CMZ) of our Galaxy. We assess the degree of star formation activity in that region using several tracers, and find very little. We made a large-scale, medium (2 ) resolution map in the J = 2 − 1 transition of SiO for which we find clumpy emission over a ∼ 0.• 8 × 0.• 3 sized region stretching along the Galactic plane. Toward selected positions we also took spectra in the easy-to-excite J k = 2 k − 1 k quartet of CH 3 OH and the carbon monosulfide (CS) 2 − 1 line. Throughout the cloud these CH 3 OH lines are, remarkably, several times stronger than both the CS and the SiO lines. The large widths of all the observed lines, similar to values generally found in the Galactic center, indicate a high degree of turbulence. Several high LSR velocity clumps that have 50-80 km s −1 higher velocities than the bulk of the molecular cloud appear at the same projected position as "normal" velocity material; this may indicate cloud-cloud collisions. Statistical equilibrium modeling of the CH 3 OH lines observed by us and others yields relatively high densities and moderate temperatures for a representative dual velocity position. We find 8×10 4 cm −3 /30 K for material in the G1.6−0.025 cloud and a higher temperature (190 K), but a 50% lower density in a high-velocity clump projected on the same location. Several scenarios are discussed in which shock chemistry might enhance the CH 3 OH and SiO abundances in G1.6−0.025 and elsewhere in the CMZ.

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270 pc Expanding Ring at the Galactic Centre

Cited by 74 publications

References 8 publications

Interstellar H ₃ ⁺

Interstellar H ₃ ⁺

The Galactic Center Environment

Molecules in G1.6–0.025—“HOT” Chemistry in the Absence of Star Formation at the Periphery of the Galactic Center Region

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270 pc Expanding Ring at the Galactic Centre

Cited by 74 publications

References 8 publications

Interstellar H 3 +

Interstellar H 3 +

The Galactic Center Environment

Molecules in G1.6–0.025—“HOT” Chemistry in the Absence of Star Formation at the Periphery of the Galactic Center Region

Contact Info

Product

Resources

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Interstellar H ₃ ⁺

Interstellar H ₃ ⁺