Evolution of Molecular and Atomic Gas Phases in the Milky Way

Koda, Jin; Scoville, N. Z.; Heyer, M. H.

doi:10.3847/0004-637x/823/2/76

Cited by 58 publications

(56 citation statements)

References 102 publications

(192 reference statements)

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“…the conversion of total gas mass to stars) to decrease within this radius, but it is not clear how this might relate to the rate of production of stars in dense clumps measured by the SFF. Koda et al (2016) show that the molecular gas fraction increases steadily with decreasing RGC, but we see in Figure 2 that the surface density of mass in dense clumps falls rapidly within 4 kpc (Bronfman et al 1988;Urquhart et al 2014a). The production of molecular clouds from neutral gas therefore is more efficient at small RGC where the H2/HI ratio is nearly 100% (Koda et al 2016).…”

Section: What Drives the Gradient In Sff With Rgc?mentioning

confidence: 98%

“…Koda et al (2016) show that the molecular gas fraction increases steadily with decreasing RGC, but we see in Figure 2 that the surface density of mass in dense clumps falls rapidly within 4 kpc (Bronfman et al 1988;Urquhart et al 2014a). The production of molecular clouds from neutral gas therefore is more efficient at small RGC where the H2/HI ratio is nearly 100% (Koda et al 2016). The fraction of molecular gas in the form of dense clumps within these clouds, while more or less steady, on average outside ∼4 kpc, albeit with very large, apparently random variations from cloud to cloud (Eden et al 2012(Eden et al , 2013, falls sharply inside this radius.…”

Section: What Drives the Gradient In Sff With Rgc?mentioning

confidence: 98%

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The prevalence of star formation as a function of Galactocentric radius

Ragan

Moore

Eden

et al. 2016

Mon. Not. R. Astron. Soc.

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We present large-scale trends in the distribution of star-forming objects revealed by the Hi-GAL survey. As a simple metric probing the prevalence of star formation in Hi-GAL sources, we define the fraction of the total number of Hi-GAL sources with a 70 µm counterpart as the "star-forming fraction" or SFF. The mean SFF in the inner galactic disc (3.1 kpc < R GC < 8.6 kpc) is 25%. Despite an apparent pile-up of source numbers at radii associated with spiral arms, the SFF shows no significant deviations at these radii, indicating that the arms do not affect the star-forming productivity of dense clumps either via physical triggering processes or through the statistical effects of larger source samples associated with the arms. Within this range of Galactocentric radii, we find that the SFF declines with R GC at a rate of −0.026±0.002 per kiloparsec, despite the dense gas mass fraction having been observed to be constant in the inner Galaxy. This suggests that the SFF may be weakly dependent on one or more largescale physical properties of the Galaxy, such as metallicity, radiation field, pressure or shear, such that the dense sub-structures of molecular clouds acquire some internal properties inherited from their environment.

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Section: What Drives the Gradient In Sff With Rgc?mentioning

confidence: 98%

Section: What Drives the Gradient In Sff With Rgc?mentioning

confidence: 98%

The prevalence of star formation as a function of Galactocentric radius

Ragan

Moore

Eden

et al. 2016

Mon. Not. R. Astron. Soc.

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“…There are no high-resolution HI data of M100 that allow us to distinguish the armto-inter-arm variation; these data are not available for most of the nearby galaxies also. Nonetheless, gas phase change between the arm and inter-arm regions has been observed in the Milky Way (Koda et al 2016). Interstellar gas becomes molecular as it enters spiral arms, but is dissociated back to the atomic phase upon leaving the arms.…”

Section: Kennicutt-schmidt Relationmentioning

confidence: 99%

Variation in GMC Association Properties across the Bars, Spiral Arms, Inter-arms, and Circumnuclear Region of M100 (NGC 4321) Extracted from ALMA Observations

Pan

Kuno

2017

ApJ

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We study the physical properties of giant molecular cloud associations (GMAs) in M100 (NGC 4321) using the ALMA Science Verification feathered (12-m+ACA) data in 12 CO (1-0). To examine the environmental dependence of GMA properties, GMAs are classified based on their locations in the various environments as circumnuclear ring (CNR), bar, spiral, and inter-arm GMAs. The CNR GMAs are massive and compact, while the inter-arm GMAs are diffuse with low surface density. GMA mass and size are strongly correlated, as suggested by Larson (1981). However, the diverse power-law index of the relation implies that the GMA properties are not uniform among the environments. The CNR and bar GMAs show higher velocity dispersion than those in other environments. We find little evidence for a correlation between GMA velocity dispersion and size, which indicates that the GMAs are in diverse dynamical states. Indeed, the virial parameter of GMAs spans nearly two orders of magnitude. Only the spiral GMAs are in general self-gravitating. Star formation activity of the GMAs decreases in order over the CNR, spiral, bar, and the inter-arm GMAs. The diverse GMA and star formation properties in different environments lead to variations in the Kennicutt-Schmidt relation. A combination of multiple mechanisms or gas phase change is necessary to explain the observed slopes. Comparisons of GMA properties acquired with the use of the 12-m-array observations with those from the feathered data are also presented. The results show that the missing flux and extended emission cannot be neglected for the study of environmental dependence.

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“…Recently Rice et al (2016) have shown that the brightest molecular clouds seem to be spatially correlated with the spiral structures of the Galaxy. On the other hand, Koda et al (2016) showed that there is rather modest variation of the fraction of molecular to atomic gas (about 20%) between the arm and the interarm regions of the Milky Way. These authors noticed that the main change in gas phase occurs at R gal > 6 kpc where the molecular fraction drops below 50% (see Figure 9, bottom left panel).…”

Section: Face-on Viewmentioning

confidence: 99%

“…At larger R gal , the H i surface density falls exponentially with a scale length of R HI ≈ 3.75 kpc (Kalberla & Kerp 2009). Both Nakanishi & Sofue (2016) and Koda et al (2016) showed that the fraction of the gas in molecular form, f H2 = Σ H2 /(Σ HI +Σ H2 ), declines steadily with R gal . This is also shown in the bottom left panel of Figure 9 using our estimate of Σ H2 .…”

Section: Surface Density Versus Galactic Radiusmentioning

confidence: 99%

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

Miville-Deschênes¹,

Murray²,

Lee³

2017

ApJ

360

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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Evolution of Molecular and Atomic Gas Phases in the Milky Way

Cited by 58 publications

References 102 publications

The prevalence of star formation as a function of Galactocentric radius

The prevalence of star formation as a function of Galactocentric radius

Variation in GMC Association Properties across the Bars, Spiral Arms, Inter-arms, and Circumnuclear Region of M100 (NGC 4321) Extracted from ALMA Observations

Physical Properties of Molecular Clouds for the Entire Milky Way Disk

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