A Large‐Scale CO Survey of the Galactic Center

Oka, Tomoharu; Hasegawa, Tetsuo; Sato, Fumio; Tsuboi, Masamichi; Miyazaki, Akira

doi:10.1086/313138

Cited by 232 publications

(267 citation statements)

References 29 publications

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“…An area empty of SiO sources is seen at the middle-velocity range in the central part of Figure 6a (l \ [0¡ .4È1¡ .0, V lsr \ 20È150 km s~1). This artifact is possibly caused by undersampling of sources in the central nuclear disk by IRAS PSC, because Figure 6a reveals the strongest CO and CS emission at this location Oka et al 1998 ;Tsuboi et al 1999). In fact, Shiki, Ohishi, & Deguchi (1997) found six new SiO sources toward Sgr B2 (l \ four of them fall at this missing velocity range of 0¡ .25È1¡ .0) ; 20È150 km s~1.…”

Section: Elocity Distributionmentioning

confidence: 96%

SiO Maser Survey of the Galactic Disk IRAS Sources. II. | l | ≤ 3o and | b | ≤ 3o, the Galactic Center Area

Deguchi

Fujii

Izumiura

et al. 2000

ASTROPHYS J SUPPL S

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A survey has been made in the SiO J \ 1È0, v \ 1 and 2 transitions (D43 GHz) for color-selected IRAS sources in the Galactic-center region of o l o ¹ 3¡ and o b o ¹ 3¡ using the Nobeyama 45 m telescope. We have detected 86 of 176 observed sources in the SiO masers. Distances to the sources are deduced from IRAS 12 and 25 km Ñux densities and range approximately from 5 to 12 kpc. Radial velocities of the detected sources spread between [300 and 310 km s~1. The longitude-velocity (l-v) diagram exhibits an empty region of sources at and km s~1, which is interpreted as an underl \ [0¡ .4È1¡ .0 V lsr \ 20È150 sampling e †ect of sources in the IRAS catalog at the Galactic central disk. The rotation rate, velocity dispersion, tilt angle of the rotation axis, and velocity shift at l \ 0¡ are derived by Ðtting the velocities of the sources with a straight line as a function of Galactic longitude. These quantities are compatible with those obtained from previous observations of bulge stars with o b o [ 3¡. The average radial velocity of subsamples of stars tends to increase with distance, suggesting the presence streaming motion of stars in a barlike bulge. We conclude that most of the IRAS sources in the sample belong to the bulge.

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Section: Elocity Distributionmentioning

confidence: 96%

SiO Maser Survey of the Galactic Disk IRAS Sources. II. | l | ≤ 3o and | b | ≤ 3o, the Galactic Center Area

Deguchi

Fujii

Izumiura

et al. 2000

ASTROPHYS J SUPPL S

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“…Characteristic cloud line widths are ≥20 km s −1 , compared to a few km s −1 for GMCs in the disk (e.g. Morris & Serabyn 1996;Oka et al 1998;Ferrière et al 2007). In addition, GMCs in the CMZ have higher kinetic temperatures, T k ∼ 30 to 200 K (Ao et al 2013;Mills & Morris 2013), and densities, n(H 2 ) ≥ 10 4−5 cm −3 (e.g.…”

Section: Introductionmentioning

confidence: 93%

Ionized gas at the edge of the central molecular zone

Langer

Goldsmith

Pineda

et al. 2015

A&A

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Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims. We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N + and C + .Methods. We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H 2 .Results. We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at −207 km s −1 associated with Sgr E and the other at −174 km s −1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ∼5 to 21 cm −3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H 2 layer in the −207 km s −1 cloud is ∼1−2× 10 21 cm −2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ∼7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions. The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N + and high electron density require an intense EUV field with a photon flux of order 10 6 to 10 7 photons cm −2 s −1 , and/or efficient proton charge exchange with nitrogen, at temperatures of order 10 4 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

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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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A Large‐Scale CO Survey of the Galactic Center

Cited by 232 publications

References 29 publications

SiO Maser Survey of the Galactic Disk IRAS Sources. II. | l | ≤ 3o and | b | ≤ 3o, the Galactic Center Area

SiO Maser Survey of the Galactic Disk IRAS Sources. II. | l | ≤ 3o and | b | ≤ 3o, the Galactic Center Area

Ionized gas at the edge of the central molecular zone

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

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