Effects of galactic disc inclination and resolution on observed GMC properties and Larson's scaling relations

Pan, Hsi-An; Fujimoto, Yusuke; Tasker, Elizabeth J.; Rosolowsky, Erik; Colombo, D.; Benincasa, Samantha M.; Wadsley, James

doi:10.1093/mnras/stw478

Cited by 15 publications

(19 citation statements)

References 61 publications

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“…Several studies of extragalactic GMC populations have also arrived at the same conclusion. However, in theory, it has been suggested that the constant Σ H2 may be a result of the limited surface brightness sensitivity of observations, and in reality, the Σ H2 values of GMCs span at least two orders of magnitude (Kegel 1989;Vázquez-Semadeni et al 1997;Ballesteros-Paredes & Mac Low 2002;Pan et al 2016). …”

Section: Comparison Of Gma Properties Between the Galactic Environmentsmentioning

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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Section: Comparison Of Gma Properties Between the Galactic Environmentsmentioning

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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“…Given that observational studies use a range of cloud definitions, with different clump finding algorithms and using different molecular emission lines, we keep our CO-based definition general, rather than try to match a particular observational study. Pan et al (2016) used a hydrodynamic simulation of a barred spiral galaxy to investigate how the definition of Also, we use projected sizes and compute the velocity dispersion by fitting a single Gaussian component to the CO spectrum. We exclude all clouds that show multiple peaks in their CO spectrum, as they cannot be fit with a single velocity component, and likely consist of multiple clouds that are undergoing mergers.…”

Section: Cloud Scaling Relationsmentioning

confidence: 99%

“…Given that observational studies use a range of cloud definitions, with different clump finding algorithms and using different molecular emission lines, we keep our CO-based definition general, rather than try to match a particular observational study. Pan et al (2016) used a hydrodynamic simulation of a barred spiral galaxy to investigate how the definition of 2016) also explored different definitions of GMCs in PPP or PPV space, based on either H2 or CO, using a high-resolution (3.85 M per SPH particle) resimulation of a section of a spiral galaxy simulation. They found that a PPV-based definition tends to blend clouds that would be physically separated in PPP space, although this effect is less significant if the PPV emission maps have high spatial resolution and high sensitivity.…”

Section: Cloud Scaling Relationsmentioning

confidence: 99%

Chemical evolution of giant molecular clouds in simulations of galaxies

Richings

Schaye

2016

Mon. Not. R. Astron. Soc.

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We present an analysis of Giant Molecular Clouds (GMCs) within hydrodynamic simulations of isolated, low-mass (M * ∼ 10 9 M ) disc galaxies. We study the evolution of molecular abundances and the implications for CO emission and the X CO conversion factor in individual clouds. We define clouds either as regions above a density threshold n H, min = 10 cm −3 , or using an observationally motivated CO intensity threshold of 0.25 K km s −1 . Our simulations include a non-equilibrium chemical model with 157 species, including 20 molecules. We also investigate the effects of resolution and pressure floors (i.e. Jeans limiters). We find cloud lifetimes up to ≈ 40 Myr, with a median of 13 Myr, in agreement with observations. At one tenth solar metallicity, young clouds ( 10 − 15 Myr) are underabundant in H 2 and CO compared to chemical equilibrium, by factors of ≈ 3 and 1 − 2 orders of magnitude, respectively. At solar metallicity, GMCs reach chemical equilibrium faster (within ≈ 1 Myr). We also compute CO emission from individual clouds. The mean CO intensity, I CO , is strongly suppressed at low dust extinction, A v , and possibly saturates towards high A v , in agreement with observations. The I CO −A v relation shifts towards higher A v for higher metallicities and, to a lesser extent, for stronger UV radiation. At one tenth solar metallicity, CO emission is weaker in young clouds ( 10−15 Myr), consistent with the underabundance of CO. Consequently, X CO decreases by an order of magnitude from 0 to 15 Myr, albeit with a large scatter.

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“…To what extent GMCs are gravitationally bound is still debated. Observation and global simulations suggest that the clouds are probably borderline bound with virial ratios of α ∼ 1-2 (Beaumont et al 2013;Pan et al 2016). However, measuring the virial ratio of a cloud observationally has always been challenging, arising in part from the various assumptions that have to be made (the shape , mass distribution and GMCs being isolated structures) and the results are quite uncertain, with errors of a factor of two.…”

Section: Introductionmentioning

confidence: 99%

Collision between molecular clouds – I. The effect of the cloud virial ratio in head-on collisions

Tanvir

Dale

2020

Monthly Notices of the Royal Astronomical Society

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In a series of papers we investigate the effect of collisions between turbulent molecular clouds on their structure, evolution and star formation activity. In this paper we look into the role of the clouds' initial virial ratios. Three different scenarios were examined: both clouds initially bound, one cloud bound and one unbound, and both clouds initially unbound. Models in which one or both clouds are bound generate filamentary structures aligned along the collision axis and discernible in position-position and position-velocity space. If neither cloud is bound, no filaments result. Unlike in previous simulations of collisions between smooth clouds, owing to the substructure created in the clouds by turbulence before the collisions, dissipation of kinetic energy by the collision is very inefficient and in none of our simulations is sufficient bulk kinetic energy lost to render the clouds bound. Simulations where both clouds are bound created twice as much stellar mass than the bound-unbound model, and both these scenarios produced much more stellar mass than the simulation in which both clouds are unbound. Each simulation was also compared with a control run in which the clouds do not collide. We find the bound-bound collision increases the overall star formation efficiency by a factor of approximately two relative to the control, but that the bound-unbound collision produces a much smaller increase, and the collision has very little effect on the unbound-unbound cloud collision.

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Effects of galactic disc inclination and resolution on observed GMC properties and Larson's scaling relations

Cited by 15 publications

References 61 publications

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

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

Chemical evolution of giant molecular clouds in simulations of galaxies

Collision between molecular clouds – I. The effect of the cloud virial ratio in head-on collisions

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