Distribution and Motion of Interstellar Hydrogen in the Galactic System With Particular Reference to the Region Within 3 Kiloparsecs of the Center

Rougoor, G. W.; Oort, J. H.

doi:10.1073/pnas.46.1.1

Cited by 95 publications

(38 citation statements)

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“…The most common approach among observers has been to assume simply that the gas moves in circular orbits in the form of a disk and/or several rings, possibly with an additional expansion velocity to account for the 3 kpc arm feature (feature C, e.g., Greaves & Nyman (1996); (e) from H i, Rougoor & Oort (1960); ( f ) from H i, Menon & Ciotti (1970); (g) see text Sect. 3.…”

Section: Resultsmentioning

confidence: 99%

Ground-state ammonia and water in absorption towards Sgr B2

Wirström

Bergman

Black

et al. 2010

A&A

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Context. Observations of transitions to the ground-state of a molecule are essential to obtain a complete picture of its excitation and chemistry in the interstellar medium, especially in diffuse and/or cold environments. For the important interstellar molecules H 2 O and NH 3 , these ground-state transitions are heavily absorbed by the terrestrial atmosphere, hence not observable from the ground. Aims. We attempt to understand the chemistry of nitrogen, oxygen, and their important molecular forms, NH 3 and H 2 O in the interstellar medium of the Galaxy. Methods. We have used the Odin submillimetre-wave satellite telescope to observe the ground state transitions of ortho-ammonia and ortho-water, including their 15 N, 18 O, and 17 O isotopologues, towards Sgr B2. The extensive simultaneous velocity coverage of the observations, >500 km s −1 , ensures that we can probe the conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the Galactic centre, and the more diffuse gas in the Galactic disk clouds along the line-of-sight.Results. We present ground-state NH 3 absorption in seven distinct velocity features along the line-of-sight towards Sgr B2. We find a nearly linear correlation between the column densities of NH 3 and CS, and a square-root relation to N 2 H + . The ammonia abundance in these diffuse Galactic disk clouds is estimated to be about 0.5-1 × 10 −8 , similar to that observed for diffuse clouds in the outer Galaxy. On the basis of the detection of H 18 2 O absorption in the 3 kpc arm, and the absence of such a feature in the H 17 2 O spectrum, we conclude that the water abundance is around 10 −7 , compared to ∼10 −8 for NH 3 . The Sgr B2 molecular cloud itself is seen in absorption in NH 3 , 15 NH 3 , H 2 O, H 18 2 O, and H 17 2 O, with emission superimposed on the absorption in the main isotopologues. The non-LTE excitation of NH 3 in the environment of Sgr B2 can be explained without invoking an unusually hot (500 K) molecular layer. A hot layer is similarly not required to explain the line profiles of the 1 1,0 ←1 0,1 transition from H 2 O and its isotopologues. The relatively weak 15 NH 3 absorption in the Sgr B2 molecular cloud indicates a high [ 14 N/ 15 N] isotopic ratio >600. The abundance ratio of H 18 2 O and H 17 2 O is found to be relatively low, 2.5-3. These results together indicate that the dominant nucleosynthesis process in the Galactic centre is CNO hydrogen burning.

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Section: Resultsmentioning

confidence: 99%

Ground-state ammonia and water in absorption towards Sgr B2

Wirström

Bergman

Black

et al. 2010

A&A

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“…• , two high velocity HI emission features known as the "Nuclear disk" (Rougoor & Oort 1960) and the "Molecular ring" (Scoville 1972) have been found. The "Nuclear disk" shows high negative velocity ranging from ≈−160 to −200 km s −1 , whereas the "Molecular ring" has a velocity of ≈−135 km s −1 .…”

Section: Introductionmentioning

confidence: 97%

Constraints on distances to Galactic Centre non-thermal filaments from HI absorption

Roy

2003

A&A

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Abstract. We have studied HI absorption towards three non-thermal filaments (NTFs) Sgr C, G359.54+0.18 and G359.79+0.17 using the Giant Metrewave Radio Telescope (GMRT). Our study, for the first time, constrains the distance of the Sgr C NTF and the HII region seen associated with the NTF in the sky plane, to within a few hundred parsecs from the Galactic Centre (GC). A molecular cloud with a velocity of −100 km s −1 appears to be associated with the central part of the Sgr C NTF. Our study also indicates that the Sgr C HII region is relatively farther away than the NTF along our line of sight, and thereby provides evidence against any possible interaction between the two objects. The NTF G359.54+0.18 shows weak HI absorption (4 σ detection) at a velocity of −140 km s −1 , which is the velocity of a known dense molecular cloud seen towards the NTF. This cloud is expected to be located within ∼200 pc of the GC and thereby provides a lower limit to the distance. The upper limit to the distance of this NTF from the Sun is 10.5 kpc. The distance to the NTF G359.79+0.17 is between 5.1 and 10.5 kpc from the Sun.

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“…Observations of the atomic and molecular interstellar medium in the inner Milky Way exhibit large noncircular motion of the gas (Rougoor & Oort 1960;Scoville 1972;Liszt & Burton 1978;Bally et al 1987;Oka et al 1998;Tsuboi, Handa & Ukita 1999;Sawada et al 2004;Oka et al 2005;Takeuchi et al 2010). Among various possible explanations for the noncircular motion, de Vaucouleurs (1964) raised a possibility that the gas responds to a stellar bar potential of the Milky Way.…”

Section: Introductionmentioning

confidence: 99%

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

Suzuki

Fukui

Torii

et al. 2015

Mon. Not. R. Astron. Soc.

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By performing a global magneto-hydrodynamical simulation for the Milky Way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the Galactic center region. The radial distribution of the rotation frequency in the bulge region is not monotonic in general. The amplification of the magnetic field is enhanced in regions with stronger differential rotation, because magnetorotational instability and field-line stretching are more effective. The strength of the amplified magnetic field reaches > ∼ 0.5 mG, and radial flows of the gas are excited by the inhomogeneous transport of angular momentum through turbulent magnetic field that is amplified in a spatially dependent manner. In addition, the magnetic pressuregradient force also drives radial flows in a similar manner. As a result, the simulated position-velocity diagram exhibits a time-dependent asymmetric parallelogram-shape owing to the intermittency of the magnetic turbulence; the present model provides a viable alternative to the bar-potential-driven model for the parallelogram-shape of the central molecular zone. This is a natural extension into the central few 100 pc of the magnetic activity, which is observed as molecular loops at radii from a few 100 pc to 1 kpc. Furthermore, the time-averaged net gas flow is directed outward, whereas the flows are highly time-dependent, which we discuss from a viewpoint of the outflow from the bulge.

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Distribution and Motion of Interstellar Hydrogen in the Galactic System With Particular Reference to the Region Within 3 Kiloparsecs of the Center

Cited by 95 publications

References 0 publications

Ground-state ammonia and water in absorption towards Sgr B2

Ground-state ammonia and water in absorption towards Sgr B2

Constraints on distances to Galactic Centre non-thermal filaments from HI absorption

Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

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