Statistical Properties of Molecular Clouds in the Galactic Center

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

doi:10.1086/322976

Cited by 178 publications

(279 citation statements)

References 26 publications

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“…The decrease of σ 0 with R gal inside the solar circle is less pronounced than σ v but still signifiant. This is compatible with the analysis of Oka et al (2001), who found that the σ v −R relation in the Galactic center area (R gal < 3 kpc) has a significantly larger normalization than that found at larger Galactic radii. Over the whole sample of clouds, the median value of σ 0 is 0.75 km s −1 , with a standard deviation of 0.43 km s −1 .…”

Section: Velocity-size Relationsupporting

confidence: 92%

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

Miville-Deschênes¹,

Murray²,

Lee³

2017

ApJ

359

303

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This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the 12 CO emission observed within b ± 5• . The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame et al. data. The total H 2 mass in the catalog is 1.2 × 10 9 M , in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is R ∼ 30 pc. We find that M ∝ R 2.2±0.2 , with no correlation between the cloud surface density, Σ, and R. In contrast with the general idea, we find a rather large range of values of Σ, from 2 to 300 M pc −2 , and a systematic decrease with increasing Galactic radius, R gal . The cloud velocity dispersion and the normalization σ 0 = σ v /R 1/2 both decrease systematically with R gal . When studied over the whole Galactic disk, there is a large dispersion in the line width-size relation, and a significantly better correlation between σ v and Σ R. The normalization of this correlation is constant to better than a factor of two for R gal < 20 kpc. This relation is used to disentangle the ambiguity between near and far kinematic distances. We report a strong variation of the turbulent energy injection rate. In the outer Galaxy it may be maintained by accretion through the disk and/or onto the clouds, but neither source can drive the 100 times higher cloud-averaged injection rate in the inner Galaxy.

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Section: Velocity-size Relationsupporting

confidence: 92%

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

Miville-Deschênes¹,

Murray²,

Lee³

2017

ApJ

359

303

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“…As mentioned above, there are molecular clouds in this region with velocities of −65 km s −1 and −100 km s −1 , noted by Liszt & Spiker (1995) and Oka et al (2001). Figure 38 shows contours of 1.4 GHz radio continuum emission overlaid on gray scale representing the H i optical depth at velocities of −65 km s −1 and −100 km s −1 .…”

Section: H I Absorption Toward the Sgr C Complexmentioning

confidence: 74%

A HIGH-RESOLUTION SURVEY OF H I ABSORPTION TOWARD THE CENTRAL 200 pc OF THE GALACTIC CENTER

Lang¹,

Goss²,

Cyganowski³

et al. 2010

ApJS

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We present an H i absorption survey of the central 250 pc of the Galaxy. Very Large Array observations were made at 21 cm in the DnC and CnB configurations and have a resolution of ∼15 (0.6 pc at the Galactic center (GC) distance) and a velocity resolution of ∼2.5 km s −1 . This study provides H i data with high spatial resolution, comparable with the many high-resolution observations which have been made of GC sources over the past 10 years. Here we present an overview of the H i absorption toward ∼40 well-known continuum sources and a detailed comparison of the ionized, atomic, and molecular components of the interstellar medium for the Sgr B, Radio Arc, and Sgr C regions. In these well-known regions, the atomic gas appears to be closely correlated in both velocity and distribution to the ionized and molecular gas, indicating that it resides in photodissociation regions related to the H ii regions in the GC. Toward the majority of the radio continuum sources, H i absorption by the 3 kpc arm is detected, constraining these sources to lie beyond a 5 kpc distance in the Galaxy.

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“…The data are consistent with a model of clouds in virial equilibrium, except that the observed normalization v 0 is about a factor of 2 too large. Subsequent work by Field et al (2011) has suggested that the larger than expected v 0 may result from external pressure confinement, although to a lesser extent than has been inferred for clouds in the outer Galaxy (Heyer et al 2001) or near the Galactic Center (Oka et al 2001). On the other hand, Ballesteros-Paredes et al (2011) have interpreted the Heyer et al (2009) result in terms of gravitational collapse near free-fall, which differs from the virial equilibrium prediction by a factor of √ 2 in v 0 , and thus is roughly consistent with the GRS data.…”

Section: Introductionmentioning

confidence: 90%

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

Wong

Hughes

Tokuda

et al. 2017

ApJ

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We present high-resolution (sub-parsec) observations of a giant molecular cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band 6 observations trace the bulk of the molecular gas in 12 CO(2-1) and high column density regions in 13 CO(2-1). Our target is a quiescent cloud (PGCC G282.98−32.40, which we refer to as the "Planck cold cloud" or PCC) in the southern outskirts of the galaxy where star-formation activity is very low and largely confined to one location. We decompose the cloud into structures using a dendrogram and apply an identical analysis to matched-resolution cubes of the 30 Doradus molecular cloud (located near intense star formation) for comparison. Structures in the PCC exhibit roughly 10 times lower surface density and 5 times lower velocity dispersion than comparably sized structures in 30 Dor, underscoring the non-universality of molecular cloud properties. In both clouds, structures with relatively higher surface density lie closer to simple virial equilibrium, whereas lower surface density structures tend to exhibit super-virial line widths. In the PCC, relatively high line widths are found in the vicinity of an infrared source whose properties are consistent with a luminous young stellar object. More generally, we find that the smallest resolved structures ("leaves") of the dendrogram span close to the full range of line widths observed across all scales. As a result, while the bulk of the kinetic energy is found on the largest scales, the smallscale energetics tend to be dominated by only a few structures, leading to substantial scatter in observed size-linewidth relationships.

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Statistical Properties of Molecular Clouds in the Galactic Center

Cited by 178 publications

References 26 publications

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

A HIGH-RESOLUTION SURVEY OF H I ABSORPTION TOWARD THE CENTRAL 200 pc OF THE GALACTIC CENTER

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

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