scholarly journals Cluster Assembly in Hierarchically Collapsing Clouds

2015 ◽  
Vol 12 (S316) ◽  
pp. 196-201
Author(s):  
Enrique Vázquez-Semadeni ◽  
Alejandro González-Samaniego ◽  
Manuel Zamora-Avilés ◽  
Pedro Colín
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Fractal Structure ◽  
Cluster Formation ◽  
Formation Rate ◽  
Structural Features ◽  
Open Clusters ◽  
Small Scale ◽  
Cluster Assembly ◽  
Scale Free

AbstractWe discuss the mechanism of cluster formation in hierarchically collapsing molecular clouds. Recent evidence, both observational and numerical, suggests that molecular clouds (MCs) may be undergoing global, hierarchical gravitational collapse. The “hierarchical” regime consists of small-scale collapses within larger-scale ones. The latter implies that the star formation rate increases systematically during the early stages of evolution, and occurs via filamentary flows onto “hubs” of higher density, mass, and velocity dispersion, and culminates a few Myr after than the small-scale collapses have started to form stars. In turn, the small-scale collapses occur in clumps embedded in the filaments, and are themselves falling into the larger potential well of the still-ongoing large-scale collapse. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps towards the larger potential trough, so that the filaments feed both gaseous and stellar material to the hubs. This leads to the presence of older stars in a region where new protostars are still forming, to a scale-free or fractal structure of the clusters, in which each unit is composed of smaller-scale ones, and to the eventual merging of the subunits, explaining the observed structural features of open clusters.

scholarly journals Scale Free Processes in Stellar Cluster Formation

2015 ◽  
Vol 11 (A29B) ◽  
pp. 717-718
Author(s):  
Nate Bastian
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Cluster Formation ◽  
Formation Rate ◽  
Stellar Clusters ◽  
Host Galaxies ◽  
Stellar Cluster ◽  
Scale Free ◽  
Model Predictions ◽  
The Common

AbstractWe review some of the basic population properties of stellar clusters, as well as how they relate to star-formation more broadly within their host galaxies. Despite the common assertion, the vast majority of stars do not form within stellar clusters. For typical galaxies (including the solar neighbourhood), the fraction of stars forming in clusters is ~10%. There are indications however that this fraction increases as a function of increasing star-formation rate surface density, in agreement with model predictions (based on a turbulent ISM and relatively straight-forward prescriptions of star-formation).

scholarly journals Filament Formation in Molecular Clouds as a Scale-Free Process

2015 ◽  
Vol 11 (A29B) ◽  
pp. 709-710
Author(s):  
Enrique Vázquez-Semadeni ◽  
Gilberto Gómez
Keyword(s):  
Hierarchical Structure ◽  
Molecular Clouds ◽  
Large Scale ◽  
Filament Formation ◽  
Molecular Line ◽  
Scale Free ◽  
The Core ◽  
Free Process ◽  
Self Gravity

AbstractWe discuss the formation of filaments in molecular clouds (MCs) as the result of large-scale collapse in the clouds. We first give arguments suggesting that self-gravity dominates the nonthermal motions, and then briefly describe the resulting structure, similar to that found in molecular-line and dust observations of the filaments in the clouds. The filaments exhibit a hierarchical structure in both density and velocity, suggesting a scale-free nature, similar to that of the cosmic web, resulting from the domination of self-gravity from the MC down to the core scale.

scholarly journals CS Lines and Dust Continuum Observations of the OMC2 Infrared Cluster

1994 ◽  
Vol 140 ◽  
pp. 245-246
Author(s):  
T. Umemoto ◽  
N. Ohashi ◽  
Y. Murata ◽  
K. Tatematsu ◽  
M. Suzuki
Keyword(s):  
Formation Process ◽  
Molecular Clouds ◽  
Large Scale ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Cluster Formation ◽  
Young Stars ◽  
Ir Sources ◽  
Near Ir ◽  
Molecular Core

It is known that stars in GMCs are often born as clusters. Recently, near infrared imaging has enabled us to study the young stars within molecular clouds (e.g., Lada & Lada 1991). Orion Molecular Cloud 2 (OMC2) is located 12' north of the Trapezium cluster in the Orion A cloud, and contains a cluster of about 20 near-IR sources and several FIR sources distributed within a diameter of 0.2 pc (Rayner et al... 1989; Johnson et al. 1990; Mezger, Wink, & Zylka 1990). By large scale mapping observations using the NRO 45 m telescope, this infrared cluster is found to be associated with a dense molecular core (Tatematsu et al. 1993, Umemoto et al. 1993). The region was observed using the Nobeyama Millimeter Array (NMA) to elucidate the structure and cluster formation process within a core.

scholarly journals MaBμlS-2: high-precision microlensing modelling for the large-scale survey era

2020 ◽  
Vol 498 (2) ◽  
pp. 2196-2218
Author(s):  
David Specht ◽  
Eamonn Kerins ◽  
Supachai Awiphan ◽  
Annie C Robin
Keyword(s):  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Near Infrared ◽  
Event Rate ◽  
Structural Features ◽  
Small Scale ◽  
Stellar Kinematics ◽  
Full Account ◽  
Space Telescope

ABSTRACT Galactic microlensing datasets now comprise in excess of 104 events and, with the advent of next-generation microlensing surveys that may be undertaken with facilities such as the Rubin Observatory (formerly LSST) and Roman Space Telescope (formerly WFIRST), this number will increase significantly. So too will the fraction of events with measurable higher order information, such as finite-source effects and lens–source relative proper motion. Analysing such data requires a more sophisticated Galactic microlens modelling approach. We present a new second-generation Manchester–Besançon Microlensing Simulator (MaBμlS-2), which uses a version of the Besançon population synthesis Galactic model that provides good agreement with stellar kinematics observed by the Hubble Space Telescope (HST) towards the bulge. MaBμlS-2 provides high-fidelity signal-to-noise limited maps of the microlensing optical depth, rate and average time-scale towards a 400 deg2 region of the Galactic bulge in several optical to near-infrared pass-bands. The maps take full account of the unresolved stellar background, as well as limb-darkened source profiles. Comparing MaBμlS-2 with the efficiency-corrected OGLE-IV 8000 event sample shows a much improved agreement over the previous version of MaBμlS and succeeds in matching even small-scale structural features in the OGLE-IV event rate map. However, evidence remains for a small underprediction of the event rate per source and overprediction of the time-scale. MaBμlS-2 is available online (www.mabuls.net, Specht & Kerins) to provide on-the-fly maps for user-supplied cuts in survey magnitude, event time-scale and relative proper motion.

scholarly journals Trade, migration, and the dynamics of spatial interaction

2019 ◽  
Author(s):  
Nicolas Gauthier
Keyword(s):  
Social Interaction ◽  
Settlement Patterns ◽  
Large Scale ◽  
Spatial Interaction ◽  
Interaction Model ◽  
Structural Features ◽  
Small Scale ◽  
Interaction Models ◽  
Road Map ◽  
Migration Flows

Archaeological settlement patterns are the physical remains of complex webs of human decision-making and social interaction. Entropy-maximizing spatial interaction models are a means of building parsimonious models that average over much of this small-scale complexity, while maintaining key large-scale structural features. Dynamic social interaction models extend this approach by allowing archaeologists to explore the co-evolution of human settlement systems and the networks of interaction that drive them. Yet, such models are often imprecise, relying on generalized notions of settlement "influence" and "attractiveness" rather than concrete material flows of goods and people. Here, I present a dis-aggregated spatial interaction model that explicitly resolves trade and migration flows and their combined influence on settlement growth and decline. I explore how the balance of costs and benefits of each type of interaction influence long-term settlement patterns. I find trade flows are the strongest determinant of equilibrium settlement structure, and that migration flows play a more transient role in balancing site hierarchies. This model illustrates how the broad toolkit for spatial interaction modeling developed in geography and economics can increase the precision of quantitative theory building in archaeology, and provides a road-map for connecting mechanistic models to the empirical archaeological record.

scholarly journals CHaMP: From Molecular Clouds to Massive Young Clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 123-124
Author(s):  
Peter J. Barnes
Keyword(s):  
Molecular Clouds ◽  
Star Formation Rate ◽  
Large Fraction ◽  
Cluster Formation ◽  
Formation Rate ◽  
Disk Galaxies ◽  
Pressure Threshold ◽  
Medium Mass ◽  
Uniform Sample ◽  
Massive Cluster

AbstractI review the major science outcomes to date of the Galactic Census of High- and Medium-mass Protostars (CHaMP), and also report the latest observational results on this unbiased, uniform sample of massive, cluster-forming molecular clumps, based on new mm-wave and IR data. These clouds represent the vast, subthermally-excited population of clumps predicted by Narayanan et al. (2008) to dominate the molecular mass of disk galaxies. Besides confirming their existence, we have presented evidence that these massive clumps probably spend a large fraction (90–95%) of their long lives (possibly up to 100 Myr) in a mostly quiescent, low star formation rate (SFR) state. This is likely ended when a density or internal pressure threshold is crossed, after which vigorous, massive cluster formation consumes the densest gas with a high SFR, dispersing the embedding envelope. New results presented in two other posters at this Symposium include (1) the first analysis of HCN emission from the dense gas (Schap et al.2015), and (2) the first deep photometry of clusters in this sample based on NIR AAT & CTIO data, and on MIR Warm Spitzer IRAC data (Dallilar et al.2015).

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.

scholarly journals Effects of clouds on the UV Absorbing Aerosol Index from TROPOMI

2020 ◽  
Vol 13 (12) ◽  
pp. 6407-6426
Author(s):  
Maurits L. Kooreman ◽  
Piet Stammes ◽  
Victor Trees ◽  
Maarten Sneep ◽  
L. Gijsbert Tilstra ◽  
...  
Keyword(s):  
Large Scale ◽  
Scale Effects ◽  
Cloud Model ◽  
Structural Features ◽  
Homogeneous Distribution ◽  
Small Scale ◽  
Retrieval Models ◽  
Cloud Models ◽  
Absorbing Aerosols ◽  
Aerosol Index

Abstract. The ultraviolet (UV) Absorbing Aerosol Index (AAI) is widely used as an indicator for the presence of absorbing aerosols in the atmosphere. Here we consider the TROPOMI AAI based on the 340 nm/380 nm wavelength pair. We investigate the effects of clouds on the AAI observed at small and large scales. The large-scale effects are studied using an aggregate of TROPOMI measurements over an area mostly devoid of absorbing aerosols (Pacific Ocean). The study reveals that several structural features can be distinguished in the AAI, such as the cloud bow, viewing zenith angle dependence, sunglint, and a previously unexplained increase in AAI values at extreme viewing and solar geometries. We explain these features in terms of the bidirectional reflectance distribution function (BRDF) of the scene in combination with the different ratios of diffuse and direct illumination of the surface at 340 and 380 nm. To reduce the dependency on the BRDF and homogenize the AAI distribution across the orbit, we present three different AAI retrieval models: the traditional Lambertian scene model (LSM), a Lambertian cloud model (LCM), and a scattering cloud model (SCM). We perform a model study to assess the propagation of errors in auxiliary databases used in the cloud models. The three models are then applied to the same low-aerosol region. Results show that using the LCM and SCM gives on average a higher AAI than the LSM. Additionally, a more homogeneous distribution is retrieved across the orbit. At the small scale, related to the high spatial resolution of TROPOMI, strong local increases and decreases in AAI are observed in the presence of clouds. The BRDF effect presented here is a first step – more research is needed to explain the small-scale cloud effects on the AAI.

scholarly journals Disk-halo interactions: molecular clouds in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 177-181
Author(s):  
D. Riquelme ◽  
J. Martín-Pintado ◽  
R. Mauersberger ◽  
S. Martín ◽  
L. Bronfman
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Center ◽  
Galactic Disk ◽  
Isotopic Ratio ◽  
Small Scale ◽  
Kinetic Temperature ◽  
Temperature Regimes ◽  
Gas Accretion

AbstractWe study the disk-halo interaction, in the context of orbits and Giant Molecular loops (GMLs) in the Galactic center (GC) region. From a large scale survey of the central kpc of the Galaxy, in SiO J = (2 − 1), HCO+J = (1 − 0) and H13CO+J = (1 − 0) molecular emission, we identify shock regions traced by the enhancement of the SiO. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the GMLs and the x1 orbits than for the GC standard molecular clouds (20–25). The high isotopic ratios are consistent with the accretion of the gas from the halo and from the outskirts of the Galactic disk. From multi-transitional observations of NH3, we derive two kinetic temperature regimes (one warm at ∼150 K and one cold at ∼40 K) for all the positions, except for the GMLs positions where only the warm component is present. The fractional abundances derived from the different molecules support the shock origin for the heating mechanism in the GC. We also present a detailed study of one molecular cloud placed in the foot points of two giant molecular loops, where two of the previously selected positions are placed. Using the 22m Mopra telescope we mapped the molecular cloud M − 3.8 + 0.9 in 3-mm molecular lines. The data show structures at small scale in SiO emission, with narrower line profiles than those of, e.g, HCO+ or HCN, which indicate that the shocks are dynamically confined. The data also show clear differences between different molecular tracers, e.g., between the SiO and HCO+ emission, which would indicate differences in the physical properties and chemistry within the cloud.

Transient 3D Simulation of the Turbulent Gas Solid Flow in Large Scale Risers Using a Density Based Solution Algorithm

2002 ◽  
Author(s):  
Asit K. Das ◽  
Gorik Van Engelandt ◽  
Guy B. Marin ◽  
Geraldine J. Heynderickx
Keyword(s):  
Large Scale ◽  
Cluster Formation ◽  
Large Diameter ◽  
Low Frequency ◽  
Solution Algorithm ◽  
3D Simulation ◽  
Small Scale ◽  
Two Phase ◽  
Solid Flow ◽  
Real Time Scale

Transient 3D simulation of the gas-solid flow in large diameter (> 0.3 m) risers is performed using a new density based solution algorithm. Unlike the conventional pressure based algorithm used so far for riser simulation, the density based solution method uses the pre-conditioning of time derivatives, does not have the internal pressure and velocity correction loop and hence provides a much faster convergence speed. The two phase flow is highly oscillatory with many small scale high frequency (10Hz) fluctuations and a few dominating low frequency (0.02 Hz) oscillations. The transient simulation of a case belonging to a fast fluidized regime with Geldart B particles, demonstrated the density inversion phenomena, experimentally observed before. Cluster formation is simulated on a real time scale for a dilute phase riser having solid fraction < 0.0007, although the time averaged flow fields still resemble a core-annular flow structure.

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