The Scale Height of Giant Molecular Clouds Is Less than That of Smaller Clouds

Stark, A. A.; Lee, Youngung

doi:10.1086/427936

Cited by 38 publications

(47 citation statements)

References 16 publications

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“…This is illustrated in Figure 3. Here we have taken the catalog subset discussed in Stark & Lee (2005), where the clouds were selected to have well-determined distances, and further restricted that subset to clouds with . Figure 3 l 1 20Њ shows the distribution of virial mass estimates for these clouds.…”

Section: Discussionmentioning

confidence: 99%

“…A catalog of clouds was generated from the Bell Laboratories survey data (Lee et al 2001) using a thresholding technique 13 CO described in Stark & Lee (2005 together in -space to make a "cloud," where all the pixels (l, b, v) constituting the cloud are above the threshold and also adjacent to at least one other pixel that is also above the threshold. A cloud is then a connected volume of pixels, all of which are above the threshold.…”

Section: Cloud Identification and Mass Estimationmentioning

confidence: 99%

“…As further described in Stark & Lee (2005), we assign several possible distances to each cloud based on our knowledge of the velocity field of the Galaxy. Essentially, the distances correspond to the "near" and "far" points of the distance ambiguity (e.g., Mihalas & Routly 1968), plus some additional uncertainty due to random motions.…”

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confidence: 99%

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Giant Molecular Clouds Are More Concentrated toward Spiral Arms than Smaller Clouds

Stark¹,

Lee²

2006

ApJ

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From our catalog of Milky Way molecular clouds, created using a temperature thresholding algorithm on the Bell Laboratories survey, we have extracted two subsets: (1) clouds that are definitely larger than 10 5 M , , 13 CO even if they are at their "near distance" (i.e., giant molecular clouds [GMCs]), and (2) clouds that are definitely smaller than 10 5 M , , even if they are at their "far distance." The positions and velocities of these clouds are compared to the loci of spiral arms in ( )-space. The radial velocity separation of each cloud from the nearest l, v spiral arm is introduced as a "concentration statistic." Almost all of the GMCs are found near spiral arms. The density of smaller clouds is enhanced near spiral arms, but some clouds (∼10% of the smaller clouds) are unassociated with any spiral arm. The median velocity separation between a GMC and the nearest spiral arm is , whereas the median separation between smaller clouds and the nearest spiral arm is Ϫ1 3.4 ‫ע‬ 0.6 km s 5.5 ‫ע‬ . These separations in radial velocity are composed partly of the velocity dispersion of the cloud Ϫ1 0.2 km s populations and partly of velocity differences due to spatial separations between the clouds and the spiral arms in the Galactic rotation field. A simple estimate indicates that the spatial separation component is relatively unimportant. The data are therefore consistent with the hypothesis that most molecular clouds in the Milky Way are spatially located in the spiral arms and that the velocity dispersion of the GMCs within the arms is less than that of the smaller clouds.

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Section: Discussionmentioning

confidence: 99%

Section: Cloud Identification and Mass Estimationmentioning

confidence: 99%

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Giant Molecular Clouds Are More Concentrated toward Spiral Arms than Smaller Clouds

Stark¹,

Lee²

2006

ApJ

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“…In other words, random velocities of molecular clouds of different masses are not expected to be in equipartition of energy (Mδv 2 /2 = const.). Observations by Stark & Lee (2005) have shown that the random velocities of low-mass molecular clouds (<2 × 10 5 M ) only vary by a factor of a few with no dependence on cloud mass. These observations are therefore more consistent with our picture than a model in which molecular clouds acquire their relative velocities via mutual gravitational interaction.…”

Section: A Scenario Of Cloud Formation Driven By Expanding Bubblesmentioning

confidence: 99%

The formation and destruction of molecular clouds and galactic star formation

Inutsuka

Inoue

Iwasaki

et al. 2015

A&A

207

216

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We describe an overall picture of galactic-scale star formation. Recent high-resolution magneto-hydrodynamical simulations of twofluid dynamics with cooling, heating, and thermal conduction have shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a scenario in which molecular clouds form in interacting shells or bubbles on a galactic scale. First, we estimated the ensemble-averaged growth rate of molecular clouds on a timescale longer than a million years. Next, we performed radiation hydrodynamics simulations to evaluate the destruction rate of magnetized molecular clouds by the stellar far-ultraviolet radiation. We also investigated the resulting star formation efficiency within a cloud, which amounts to a low value (a few percent) if we adopt the power-law exponent ∼− 2.5 for the mass distribution of stars in the cloud. We finally describe the time evolution of the mass function of molecular clouds on a long timescale (>1 Myr) and discuss the steady state exponent of the power-law slope in various environments.

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“…In other words, random velocities of molecular clouds of different masses are not expected to be in equipartition of energy (Mδv 2 /2 =const.). Observations by Stark & Lee (2005) have shown that the random velocities of low-mass molecular clouds (< 2 × 10 5 M⊙) only vary by a few, with no dependence on cloud mass. These observations are therefore more consistent with our picture than a model in which molecular clouds acquire their relative velocities via mutual gravitational interaction.…”

Section: A Scenario Of Cloud Formation Driven By Expanding Bubblesmentioning

confidence: 99%

The Formation and Destruction of Molecular Clouds and Galactic Star Formation

Inutsuka

Inoue²,

Iwasaki³

et al. 2015

Proc. IAU

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We describe an overall picture of galactic-scale star formation. Recent high-resolution magneto-hydrodynamical simulations of twofluid dynamics with cooling/heating and thermal conduction have shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a scenario in which molecular clouds form in interacting shells or bubbles on a galactic scale. First we estimate the ensemble-averaged growth rate of molecular clouds over a timescale larger than a million years. Next we perform radiation hydrodynamics simulations to evaluate the destruction rate of magnetized molecular clouds by the stellar FUV radiation. We also investigate the resultant star formation efficiency within a cloud which amounts to a low value (a few percent) if we adopt the power-law exponent ∼ −2.5 for the mass distribution of stars in the cloud. We finally describe the time evolution of the mass function of molecular clouds over a long timescale (>1Myr) and discuss the steady state exponent of the power-law slope in various environments.

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The Scale Height of Giant Molecular Clouds Is Less than That of Smaller Clouds

Cited by 38 publications

References 16 publications

Giant Molecular Clouds Are More Concentrated toward Spiral Arms than Smaller Clouds

Giant Molecular Clouds Are More Concentrated toward Spiral Arms than Smaller Clouds

The formation and destruction of molecular clouds and galactic star formation

The Formation and Destruction of Molecular Clouds and Galactic Star Formation

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