scholarly journals Simulating the chemistry and dynamics of molecular clouds

2009 ◽  
Vol 5 (H15) ◽  
pp. 405-405
Author(s):  
S. C. O. Glover ◽  
C. Federrath ◽  
M.-M. Mac Low ◽  
R. S. Klessen
Keyword(s):  
Molecular Clouds ◽  
Chemical Structure ◽  
Three Dimensional ◽  
Dynamical Evolution ◽  
Giant Molecular Clouds ◽  
Interstellar Gas ◽  
Density Inhomogeneities ◽  
First Time ◽  
Three Dimensional Simulations

AbstractWe have performed high-resolution three-dimensional simulations of turbulent interstellar gas that for the first time self-consistently follow its coupled thermal, chemical and dynamical evolution. Our simulations have allowed us to quantify the formation timescales for the most important molecules found in giant molecular clouds (H2, CO), as well as their spatial distribution within the clouds. Our results are consistent with models in which molecular clouds form quickly, within 1–2 turbulent crossing times, and emphasize the crucial role of density inhomogeneities in determining the chemical structure of the clouds.

scholarly journals Molecules in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 415-420 ◽  
Author(s):  
R. S. Booth ◽  
Th. De Graauw
Keyword(s):  
High Resolution ◽  
Molecular Clouds ◽  
Short Review ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Giant Molecular Clouds ◽  
Interstellar Molecules ◽  
First Time ◽  
Excitation Conditions

In this short review we describe recent new observations of millimetre transitions of molecules in selected regions of the Magellanic Clouds. The observations were made using the Swedish-ESO Submillimetre Telescope, SEST, (Booth et al. 1989), the relatively high resolution of which facilitates, for the first time, observations of individual giant molecular clouds in the Magellanic Clouds. We have mapped the distribution of the emission from the two lowest rotational transitions of 12CO and 13CO and hence have derived excitation conditions for the molecule. In addition, we have observed several well-known interstellar molecules in the same regions, thus doubling the number of known molecules in the Large Magellanic Cloud (LMC). The fact that all the observations have been made under controlled conditions with the same telescope enables a reasonable intercomparison of the molecular column densities. In particular, we are able to observe the relative abundances among the different isotopically substituted species of CO.

3D simulations of warm and hot Jupiter atmospheres: the role of 3D mixing in shaping CH4-to-CO conversion pathways

2021 ◽  
Author(s):  
Maria Zamyatina ◽  
Eric Hebrard ◽  
Nathan Mayne ◽  
Benjamin Drummond
Keyword(s):  
Chemical Structure ◽  
Three Dimensional ◽  
Chemical Species ◽  
Radiation Chemistry ◽  
3D Simulations ◽  
Horizontal Advection ◽  
Co Conversion ◽  
Area Of Influence ◽  
Different Parts

<p>We present results from a set of cloud-free simulations of exoplanet atmospheres using a coupled three-dimensional (3D) hydrodynamics-radiation-chemistry model. We report in particular our investigation of the thermodynamic and chemical structure of the atmospheres of HAT-P-11b and WASP-17b and their comparison with the results for the atmospheres of HD 189733b and HD 209458b presented in Drummond et al. (2020). We found that the abundances of chemical species from simulations with interactive chemistry depart from their respective abundances computed at local chemical equilibrium, especially at higher latitudes. To understand this departure, we analysed the CH<sub>4</sub>-to-CO conversion pathways within the Venot et al. (2019) reduced chemical network used in our model using a chemical network analysis. We found that at steady state nine CH<sub>4</sub>-to-CO conversion pathways manifest in our 3D simulations with interactive chemistry, with different pathways dominating different parts of the atmosphere and their area of influence being determined by the vertical and horizontal advection and shifting between planets.</p>

scholarly journals Enhanced UV radiation and dense clumps in the molecular outflow of Mrk 231

2020 ◽  
Vol 633 ◽  
pp. A163 ◽  
Author(s):  
Claudia Cicone ◽  
Roberto Maiolino ◽  
Susanne Aalto ◽  
Sebastien Muller ◽  
Chiara Feruglio
Keyword(s):  
Gas Phase ◽  
Uv Radiation ◽  
Molecular Clouds ◽  
Line Emission ◽  
Molecular Gas ◽  
Spectral Features ◽  
Giant Molecular Clouds ◽  
Dense Phase ◽  
Molecular Outflow ◽  
First Time

We present interferometric observations of the CN(1–0) line emission in Mrk 231 and combine them with previous observations of CO and other H2 gas tracers to study the physical properties of the massive molecular outflow. We find a strong boost of the CN/CO(1–0) line luminosity ratio in the outflow of Mrk 231, which is unprecedented compared to any other known Galactic or extragalactic astronomical source. For the dense gas phase in the outflow traced by the HCN and CN emissions, we infer XCN ≡ [CN]/[H2]> XHCN by at least a factor of three, with H2 gas densities of nH2 ∼ 105−6 cm−3. In addition, we resolve for the first time narrow spectral features in the HCN(1–0) and HCO+(1–0) high-velocity line wings tracing the dense phase of the outflow. The velocity dispersions of these spectral features, σv ∼ 7−20 km s−1, are consistent with those of massive extragalactic giant molecular clouds detected in nearby starburst nuclei. The H2 gas masses inferred from the HCN data are quite high, Mmol ∼ 0.3−5 × 108 M⊙. Our results suggest that massive complexes of denser molecular gas survive embedded into the more diffuse H2 phase of the outflow, and that the chemistry of these outflowing dense clouds is strongly affected by UV radiation.

scholarly journals Flow-accelerated platelet biogenesis is due to an elasto-hydrodynamic instability

2020 ◽  
Vol 117 (32) ◽  
pp. 18969-18976 ◽  
Author(s):  
Christian Bächer ◽  
Markus Bender ◽  
Stephan Gekle
Keyword(s):  
Hydrodynamic Instability ◽  
Blood Platelets ◽  
Three Dimensional ◽  
Immersed Boundary ◽  
Fusion Event ◽  
Specific Flow ◽  
Actomyosin Contractility ◽  
Biophysical Mechanism ◽  
Three Dimensional Simulations

Blood platelets are formed by fragmentation of long membrane extensions from bone marrow megakaryocytes in the blood flow. Using lattice-Boltzmann/immersed boundary simulations we propose a biological Rayleigh–Plateau instability as the biophysical mechanism behind this fragmentation process. This instability is akin to the surface tension-induced breakup of a liquid jet but is driven by active cortical processes including actomyosin contractility and microtubule sliding. Our fully three-dimensional simulations highlight the crucial role of actomyosin contractility, which is required to trigger the instability, and illustrate how the wavelength of the instability determines the size of the final platelets. The elasto-hydrodynamic origin of the fragmentation explains the strong acceleration of platelet biogenesis in the presence of an external flow, which we observe in agreement with experiments. Our simulations then allow us to disentangle the influence of specific flow conditions: While a homogeneous flow with uniform velocity leads to the strongest acceleration, a shear flow with a linear velocity gradient can cause fusion events of two developing platelet-sized swellings during fragmentation. A fusion event may lead to the release of larger structures which are observable as preplatelets in experiments. Together, our findings strongly indicate a mainly physical origin of fragmentation and regulation of platelet size in flow-accelerated platelet biogenesis.

scholarly journals Dynamical evolution of the Oort cloud

1985 ◽  
Vol 83 ◽  
pp. 87-96
Author(s):  
Paul R. Weissman
Keyword(s):  
Monte Carlo Simulation ◽  
Molecular Clouds ◽  
Dynamical Evolution ◽  
Oort Cloud ◽  
Giant Planets ◽  
Giant Molecular Clouds ◽  
The Earth ◽  
The Galaxy ◽  
Periodic Comet ◽  
Monte Carlo Simulation Model

AbstractNew studies of the dynamical evolution of cometary orbits in the Oort cloud are made using a revised version of Weissman’s (1982) Monte Carlo simulation model, which more accurately mimics the perturbation of comets by the giant planets. It is shown that perturbations by Saturn provide a substantial barrier to the diffusion of cometary perihelia into the inner solar system; Jupiter also. Perturbations by Uranus and Neptune are rarely great enough to remove comets from the Oort cloud, but do serve to scatter the comets in the cloud in 1/a. The new model gives a population of 1.8 to 2.1 × 1012 comets for the present-day Oort cloud, and a mass of 7 to 8 earth masses. Perturbation of the Oort cloud by giant molecular clouds in the galaxy is discussed, as is evidence for a massive “inner Oort cloud” internal to the observed one. The possibility of an unseen solar companion orbiting in the Oort cloud and causing periodic comet showers is shown to be dynamically plausible but unlikely based on the observed cratering rate on the earth and moon.

Three-Dimensional Characterization of a Pure Thermal Plume

2005 ◽  
Vol 127 (6) ◽  
pp. 624-636 ◽  
Author(s):  
Minh Vuong Pham ◽  
Fre´de´ric Plourde ◽  
Son Doan Kim
Keyword(s):  
Direct Method ◽  
Three Dimensional ◽  
Momentum Equation ◽  
Thermal Plume ◽  
Thermal Plumes ◽  
Heating Source ◽  
Entrainment Coefficient ◽  
Particle Imaging ◽  
First Time

Pure thermal plumes have been investigated by two-dimensional (2D) and three-dimensional (3D) particle imaging velocimetry (PIV) techniques. While classical plume features have been checked out, time-dependent analysis allows one to clearly detect contraction and expulsion phases which are mainly driven by turbulent structure behavior. Balance of momentum equation demonstrates the link between stronger structures and expulsion-contraction motion mainly dominated by plume engulfment during contraction phases. A ratio of 3 between entrained mass flow rate during contraction and expulsion phases has been estimated. A new method, never previously applied to pure thermal plume, allows one to accurately characterize entrainment mechanism and for the first time, the latter renders it possible to estimate the entrainment coefficient all along the plume height, even close to the heating source. Moreover, entrainment coefficient is found to be 20% higher with direct method as opposed to the classical differential one widely used in the literature. Such a huge gap is found to be due to the fluctuating density and velocity part. Even through it markedly contributes to an enhanced entrainment mechanism, the role of fluctuation was generally overlooked in the previous works devoted to entrainment coefficient estimate.

scholarly journals Molecular Clouds: Internal Properties, Turbulence, Star Formation and Feedback

2012 ◽  
Vol 8 (S292) ◽  
pp. 19-28 ◽  
Author(s):  
Jonathan C. Tan ◽  
Suzanne N. Shaske ◽  
Sven Van Loo
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Cluster Formation ◽  
Dynamical Evolution ◽  
Theoretical Models ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Cloud Dynamics ◽  
Star Formation Activity ◽  
Internal Properties

AbstractAll stars are born in molecular clouds, and most in giant molecular clouds (GMCs), which thus set the star formation activity of galaxies. We first review their observed properties, including measures of mass surface density, Σ, and thus mass,M. We discuss cloud dynamics, concluding most GMCs are gravitationally bound. Star formation is highly clustered within GMCs, but overall is very inefficient. We compare properties of star-forming clumps with those of young stellar clusters (YSCs). The high central densities of YSCs may result via dynamical evolution of already-formed stars during and after star cluster formation. We discuss theoretical models of GMC evolution, especially addressing how turbulence is maintained, and emphasizing the importance of GMC collisions. We describe how feedback limits total star formation efficiency, ε, in clumps. A turbulent and clumpy medium allows higher ε, permitting formation of bound clusters even when escape speeds are less than the ionized gas sound speed.

scholarly journals The role of galactic dynamics in shaping the physical properties of giant molecular clouds in Milky Way-like galaxies

2020 ◽  
Vol 498 (1) ◽  
pp. 385-429 ◽  
Author(s):  
Sarah M R Jeffreson ◽  
J M Diederik Kruijssen ◽  
Benjamin W Keller ◽  
Mélanie Chevance ◽  
Simon C O Glover
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Milky Way ◽  
Gravitational Instability ◽  
Formation Rate ◽  
Tangential Velocity ◽  
Galactic Rotation ◽  
H Ii Regions ◽  
Giant Molecular Clouds

ABSTRACT We examine the role of the large-scale galactic-dynamical environment in setting the properties of giant molecular clouds in Milky Way-like galaxies. We perform three high-resolution simulations of Milky Way-like discs with the moving-mesh hydrodynamics code arepo, yielding a statistical sample of ${\sim}80\, 000$ giant molecular clouds and ${\sim}55\, 000$ H i clouds. We account for the self-gravity of the gas, momentum, and thermal energy injection from supernovae and H ii regions, mass injection from stellar winds, and the non-equilibrium chemistry of hydrogen, carbon, and oxygen. By varying the external gravitational potential, we probe galactic-dynamical environments spanning an order of magnitude in the orbital angular velocity, gravitational stability, mid-plane pressure, and the gradient of the galactic rotation curve. The simulated molecular clouds are highly overdense (∼100×) and overpressured (∼25×) relative to the ambient interstellar medium. Their gravoturbulent and star-forming properties are decoupled from the dynamics of the galactic mid-plane, so that the kpc-scale star formation rate surface density is related only to the number of molecular clouds per unit area of the galactic mid-plane. Despite this, the clouds display clear, statistically significant correlations of their rotational properties with the rates of galactic shearing and gravitational free-fall. We find that galactic rotation and gravitational instability can influence their elongation, angular momenta, and tangential velocity dispersions. The lower pressures and densities of the H i clouds allow for a greater range of significant dynamical correlations, mirroring the rotational properties of the molecular clouds, while also displaying a coupling of their gravitational and turbulent properties to the galactic-dynamical environment.

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