scholarly journals Size distribution of superbubbles

2020 ◽  
Vol 493 (1) ◽  
pp. 1034-1043 ◽  
Author(s):  
Biman B Nath ◽  
Pushpita Das ◽  
M S Oey
Keyword(s):  
Size Distribution ◽  
Milky Way ◽  
Ambient Medium ◽  
Thermal Pressure ◽  
Star Forming ◽  
Shock Speed ◽  
Ambient Sound ◽  
Pressure Equilibrium ◽  
Higher Temperature ◽  
Self Similar

ABSTRACT We consider the size distribution of superbubbles in a star-forming galaxy. Previous studies have tried to explain the distribution by using adiabatic self-similar evolution of wind-driven bubbles, assuming that bubbles stall when pressure equilibrium is reached. We show, with the help of hydrodynamical numerical simulations, that this assumption is not valid. We also include radiative cooling of shells. In order to take into account non-thermal pressure in the ambient medium, we assume an equivalent higher temperature than implied by thermal pressure alone. Assuming that bubbles stall when the outer shock speed becomes comparable to the ambient sound speed (which includes non-thermal components), we recover the size distribution with a slope of ∼−2.7 for typical values of interstellar medium pressure in Milky Way, which is consistent with observations. Our simulations also allow us to follow the evolution of size distribution in the case of different values of non-thermal pressure, and we show that the size distribution steepens with lower pressure, to slopes intermediate between only-growing and only-stalled cases.

Phase equilibria in NaAlSiO4–KAlSiO4–SiO2–H2O at 100 MPa pressure: equilibrium leucite composition and the enigma of primary analcime in blairmorites revisited

2014 ◽  
Vol 78 (1) ◽  
pp. 171-202 ◽  
Author(s):  
C. M. B. Henderson ◽  
D. L. Hamilton ◽  
J. P. Waters
Keyword(s):  
Mineral Assemblage ◽  
Volcanic Rocks ◽  
Stoichiometric Composition ◽  
Pressure Equilibrium ◽  
Upward Transport ◽  
Higher Temperature ◽  
Invariant Points ◽  
Water Saturated ◽  
Low K ◽  
Maximum Content

AbstractExperiments in the system NaAlSiO4(Ne)−KAlSiO4(Ks)−SiO2(Qz)−H2O at 100 MPa show that the maximum content of NaAlSi2O6 in leucite is ∼4 wt.% and that analcime is close to the stoichiometric composition (NaAlSi2O6.H2O). Analcime forms metastably on quenching the higher-temperature experiments; it is secondary after leucite in experiments quenched from 780°C, while from 850°C it forms by alteration of leucite, and by devitrification of water-saturated glass. Both processes involve reaction with Na-rich aqueous fluids. Stable analcime forms at 500°C, well below the solidus, and cannot form as phenocrysts in shallow volcanic systems. New data for natural analcime macrocrysts in blairmorites are presented for the Crowsnest volcanics, Alberta, Canada. Other researchers have suggested that primary analcime occurs as yellow-brown, glassy, analcime phenocrysts. Our microprobe analyses show that such primary analcime is close to stoichiometric, with very low K2O (<0.1 wt.%), minor Fe2O3 (0.5−0.8 wt.%) and CaO (∼0.5 wt.%). An extrapolation of published experimental data for Ne−Ks−Qz at >500 MPa PH2O, where Anl + melt coexist, suggests that at >800 MPa two invariant points are present: (1) a reaction point involving Kf + Ab + Anl + melt + vapour; and (2) a eutectic with Kf + Anl + Ne + melt + vapour. We suggest that the nepheline-free equilibrium mineral assemblage for Crowsnest samples is controlled by reaction point (1). In contrast, blairmorites from Lupata Gorge, Mozambique, form at eutectic (2), consistent with the presence of nepheline phenocrysts. Our conclusions, based on high- vs. low-pressure experiments, confirm the suggestion made by other authors, that Crowsnest volcanic rocks must have been erupted explosively to preserve glassy analcime phenocrysts during very rapid, upward transport from deep in the crust (H2O pressures ≫500 MPa). Only rare examples survived the deuteric and hydrothermal alteration that occurred during and after eruption.

scholarly journals Evaluation of hadronic emission in starburst galaxies and star-forming galaxies

2021 ◽  
Vol 21 (10) ◽  
pp. 263
Author(s):  
Yun-Chuan Xiang ◽  
Ze-Jun Jiang ◽  
Yun-Yong Tang
Keyword(s):  
Supernova Remnants ◽  
Milky Way ◽  
Starburst Galaxies ◽  
Model Parameters ◽  
Zone Model ◽  
Observation Data ◽  
Large Area ◽  
Star Forming ◽  
Ngc 1068 ◽  
The One

Abstract In this work, we reanalyzed 11 years of spectral data from the Fermi Large Area Telescope (Fermi-LAT) of currently observed starburst galaxies (SBGs) and star-forming galaxies (SFGs). We used a one-zone model provided by NAIMA and the hadronic origin to explain the GeV observation data of the SBGs and SFGs. We found that a protonic distribution of a power-law form with an exponential cutoff can explain the spectra of most SBGs and SFGs. However, it cannot explain the spectral hardening components of NGC 1068 and NGC 4945 in the GeV energy band. Therefore, we considered the two-zone model to well explain these phenomena. We summarized the features of two model parameters, including the spectral index, cutoff energy, and proton energy budget. Similar to the evolution of supernova remnants (SNRs) in the Milky Way, we estimated the protonic acceleration limitation inside the SBGs to be the order of 102 TeV using the one-zone model; this is close to those of SNRs in the Milky Way.

scholarly journals The Role of Saccharomyces cerevisiae Yeast and Lactic Acid Bacteria in the Formation of 2-Propanol from Acetone during Fermentation of Rye Mashes Obtained Using Thermal-Pressure Method of Starch Liberation

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 610 ◽  
Author(s):  
Katarzyna Pielech-Przybylska ◽  
Maria Balcerek ◽  
Urszula Dziekońska-Kubczak ◽  
Barbara Pacholczyk-Sienicka ◽  
Grzegorz Ciepielowski ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Thermal Pressure ◽  
Yellowness Index ◽  
Pressure Method ◽  
Fermentation Temperature ◽  
L Value ◽  
Higher Temperature ◽  
Positive Correlations

This study set out to assess the acetone content in rye sweet mashes prepared using the thermal-pressure method of starch liberation, and to investigate the formation of 2-propanol during the fermentation process. In the first set of experiments, we evaluated the correlation between the color and the content of acetone and furfural in industrially produced sweet mashes (n = 37). The L * value was negatively correlated with the content of both acetone and furfural, while chromatic parameters a * and b * and the yellowness index (YI) had strong positive correlations with acetone (r > 0.9) and furfural (r > 0.8 for a * and r > 0.9 for b * and YI). In the second set of experiments, we assessed the concentration of acetone and 2-propanol in distillery rye mashes, fermented by S. cerevisiae yeast and lactic acid bacteria. The influence of fermentation temperature on the formation of 2-propanol was also evaluated. The presence of 2-propanol in the post-fermentation media was confirmed, while a decrease in acetone content was observed. Fermentation temperature (27 °C or 35 °C) was found to have a significant effect on the concentration of 2-propanol in trials inoculated with lactic bacteria. The content of 2-propanol was more than 11 times higher in trials fermented at the higher temperature. In the case of yeast-fermented mashes, the temperature did not affect 2-propanol content. The acetone in the sweet mash was assumed to be a precursor of 2-propanol, which was found in the fermented mashes.

scholarly journals Effect of ambient wind velocity on Planetary Nebula morphology

1997 ◽  
Vol 180 ◽  
pp. 224-224
Author(s):  
Vikram V. Dwarkadas ◽  
Roger A. Chevalier ◽  
John M. Blondin
Keyword(s):  
Wind Velocity ◽  
Ambient Medium ◽  
Asymptotic Giant Branch ◽  
Density Contrast ◽  
Expansion Velocity ◽  
Ambient Wind ◽  
Pn Velocity ◽  
Fast Wind ◽  
Self Similar ◽  
Slow Wind

Planetary Nebulae (PNe) are formed by the interaction of the fast wind from a post-Asymptotic Giant Branch Star with the slow ambient wind from a previous epoch. If the two interacting winds have constant properties, the velocity of the PN shell tends towards a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. Using semi-analytical methods, complemented by hydrodynamic simulations, we have calculated the shapes of PNe in the self-similar stage (Dwarkadas et al. 1996). We have investigated the contribution of the ambient wind velocity to PN morphology, which has hitherto not received much attention since the work of Kahn & West (1985). We find that the nebular morphology is a consequence of the density contrast between pole and equator in the ambient medium, the steepness of the density profile and the velocity of the ambient wind; classification of PNe purely on the basis of the first two factors may be misleading. In particular, the ratio of ambient wind velocity to PN velocity is important in determining whether the nebula shows a bulge or a cusp at the equator. A high density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximum of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. As long as the external wind velocity is small compared to the expansion velocity of the nebula, the PNe tend to be more bipolar, even with a moderate density contrast. If the PN velocity is close to that of the external wind, the shape is relatively spherical. However, inclusion of an asymmetric velocity profile in the slow wind, with the velocity increasing towards the pole, can lead to a bipolar nebula if the equatorial velocity is sufficiently low. Preliminary results with a slow wind velocity increasing towards the equator (as is found in calculations of common envelope evolution) show that the nebulae tend to be more oblate, which is not often observed in nature. Representative results for shapes of PNe using various values of the relevant parameters are presented.

scholarly journals Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness

2020 ◽  
Vol 497 (3) ◽  
pp. 3830-3845 ◽  
Author(s):  
Hajime Fukushima ◽  
Hidenobu Yajima ◽  
Kazuyuki Sugimura ◽  
Takashi Hosokawa ◽  
Kazuyuki Omukai ◽  
...  
Keyword(s):  
Star Formation ◽  
Massive Stars ◽  
Cluster Formation ◽  
Star Clusters ◽  
Star Cluster ◽  
Star Forming ◽  
Dynamical Time ◽  
Low Metallicity ◽  
Higher Temperature ◽  
Dust Attenuation

ABSTRACT We study star cluster formation in various environments with different metallicities and column densities by performing a suite of 3D radiation hydrodynamics simulations. We find that the photoionization feedback from massive stars controls the star formation efficiency (SFE) in a star-forming cloud, and its impact sensitively depends on the gas metallicity Z and initial cloud surface density Σ. At Z = 1 Z⊙, SFE increases as a power law from 0.03 at Σ = 10 M⊙ pc−2 to 0.3 at $\Sigma = 300\,\mathrm{M}_{\odot }\, {\rm pc^{-2}}$. In low-metallicity cases $10^{-2}\!-\!10^{-1}\, \mathrm{Z}_{\odot }$, star clusters form from atomic warm gases because the molecule formation time is not short enough with respect to the cooling or dynamical time. In addition, the whole cloud is disrupted more easily by expanding H ii bubbles that have higher temperature owing to less efficient cooling. With smaller dust attenuation, the ionizing radiation feedback from nearby massive stars is stronger and terminate star formation in dense clumps. These effects result in inefficient star formation in low-metallicity environments: the SFE drops by a factor of ∼3 at Z = 10−2 Z⊙ compared to the results for Z = 1 Z⊙, regardless of Σ. Newborn star clusters are also gravitationally less bound. We further develop a new semi-analytical model that can reproduce the simulation results well, particularly the observed dependencies of the SFEs on the cloud surface densities and metallicities.

scholarly journals Was the Milky Way Bulge Formed from the Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?

2017 ◽  
Vol 34 ◽  
Author(s):  
David M. Nataf
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Velocity Dispersion ◽  
High Redshift ◽  
Rapid Development ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Thin And Thick Disks ◽  
Bulge Formation ◽  
Redshift Galaxies

AbstractThe assembly of the Milky Way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. That is due to tremendous advances in observations of bulge stars, motivating observations of both local and high-redshift galaxies, and increasingly sophisticated simulations. The dominant scenario for bulge formation is that of the Milky Way as a nearly pure disk galaxy, with the inner disk having formed a bar and buckled. This can potentially explain virtually all bulge stars with [Fe/H] ≳ −1.0, which comprise 95% of the stellar population. The evidence is the incredible success in N-body models of this type in making non-trivial, non-generic predictions, such as the rotation curve and velocity dispersion measured from radial velocities, and the spatial morphologies of the peanut/X-shape and the long bar. The classical bulge scenario, whereby the bulge formed from early dissipative collapse and mergers, remains viable for stars with [Fe/H] ≲ −1.0 and potentially a minority of the other stars. A classical bulge is expected from Λ-CDM cosmological simulations, can accentuate the properties of an existing bar in a hybrid system, and is most consistent with the bulge abundance trends such as [Mg/Fe], which are elevated relative to both the thin and thick disks. Finally, the clumpy-galaxy scenario is considered, as it is the correct description of most Milky Way precursors given observations of high-redshift galaxies. Simulations predict that these star-forming clumps will sometimes migrate to the centres of galaxies where they may form a bulge, and galaxies often include a bulge clump as well. They will possibly form a bar with properties consistent with those of the Milky Way, such as the exponential profile and metallicity gradient. Given the relative successes of these scenarios, the Milky Way bulge is plausibly of composite origin, with a classical bulge and/or inner halo numerically dominant for stars with [Fe/H] ≲ −1.0, a buckling thick disk for stars with − 1.0 ≲ [Fe/H]] ≲ -0.50 perhaps descended from the clumpy-galaxy phase, and a buckling thin disk for stars with [Fe/H] ≳ −0.50. Overlaps from these scenarios are uncertain throughout.

scholarly journals A laboratory study of sediment deformation: stress heterogeneity and grain-size evolution

1996 ◽  
Vol 22 ◽  
pp. 167-175 ◽  
Author(s):  
Neal R. Iverson ◽  
Thomas S. Hooyer ◽  
Roger Leb. Hooke
Keyword(s):  
Grain Size ◽  
Fractal Dimension ◽  
Normal Stress ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Local Stress ◽  
Large Strains ◽  
Self Similar ◽  
Deformation Stress ◽  
Stress Heterogeneity

In shearing sediment beneath glaciers, networks of grains may transiently support shear and normal stresses that are larger than spatial averages. Consistent with studies of fault-gouge genesis, we hypothesize that crushing of grains in such networks is responsible for surrounding larger grains with smaller grains. At sufficiently large strains, this should minimize stress heterogeneity, favor intergranular sliding and abrasion rather than crushing, and result in a self-similar grain-size distribution.This hypothesis is tested with a ring-shear device that slowly shears a large annular sediment sample to high strains. Shearing and comminution of weak equigranular (2.0–3.3 mm) sediment resulted in a self-similar grain-size distribution with a fractal dimension that increased with shear strain toward a steady value of 2.85. This value is significantly larger than that of gouges produced purely by crushing, 2.6, but it is comparable to values for tilts thought to be deforming beneath modern glaciers, 2.8 to nearly 3.0. At low strains, under a steady mean normal stress of 84 kPa, variations in normal stress measured locally ranged in amplitude from 50 to 300 kPa with wavelengths that were 100 times larger than the initial grain diameter. Crushing of grains, observed through the transparent walls of the device, apparently caused the failure of grain networks. At shearing displacements ranging from 0.7 to 1.0 m, the amplitude of local stress fluctuations decreased abruptly. This change is attributed to fine sediment that distributed stresses more uniformly and caused grain networks to fail primarily by intergranular sliding rather than by crushing of grains. Sliding between grains apparently produced silt by abrasion and resulted in a fractal dimension that was higher than if there had been only crushing.A size distribution with a fractal dimension greater than 2.6 is probably a necessary but not sufficient condition for determining whether a basal till has been highly deformed. Stress heterogeneity in subglacial sediment that is shearing through its full thickness should contribute to the erosion of underlying rock.

scholarly journals Milky Way analogues in MaNGA: multiparameter homogeneity and comparison to the Milky Way

2019 ◽  
Vol 491 (3) ◽  
pp. 3672-3701 ◽  
Author(s):  
N Boardman ◽  
G Zasowski ◽  
A Seth ◽  
J Newman ◽  
B Andrews ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Milky Way ◽  
Central Star ◽  
Stellar Kinematics ◽  
Star Forming ◽  
Wide Range ◽  
The Galaxy ◽  
Central Regions ◽  
Galaxy Population ◽  
Stellar Masses

ABSTRACT The Milky Way provides an ideal laboratory to test our understanding of galaxy evolution, owing to our ability to observe our Galaxy over fine scales. However, connecting the Galaxy to the wider galaxy population remains difficult, due to the challenges posed by our internal perspective and to the different observational techniques employed. Here, we present a sample of galaxies identified as Milky Way analogues on the basis of their stellar masses and bulge-to-total ratios, observed as part of the Mapping Nearby Galaxies at Apache Point Observatory survey. We analyse the galaxies in terms of their stellar kinematics and populations as well as their ionized gas contents. We find our sample to contain generally young stellar populations in their outskirts. However, we find a wide range of stellar ages in their central regions, and we detect central active galactic nucleus-like or composite-like activity in roughly half of the sample galaxies, with the other half consisting of galaxies with central star-forming emission or emission consistent with old stars. We measure gradients in gas metallicity and stellar metallicity that are generally flatter in physical units than those measured for the Milky Way; however, we find far better agreement with the Milky Way when scaling gradients by galaxies’ disc scale lengths. From this, we argue much of the discrepancy in metallicity gradients to be due to the relative compactness of the Milky Way, with differences in observing perspective also likely to be a factor.

scholarly journals The vertical metallicity gradients of mono-age stellar populations in the Milky Way thin disk

2017 ◽  
Vol 13 (S334) ◽  
pp. 281-282
Author(s):  
Ioana Ciucă ◽  
Daisuke Kawata ◽  
Jane Lin ◽  
Luca Casagrande ◽  
George Seabroke ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Stellar Populations ◽  
Thin Disk ◽  
Dwarf Stars ◽  
Star Forming ◽  
Data Release ◽  
The Cross

AbstractWe investigate the vertical metallicity gradients of five mono-age stellar populations between 0 and 11 Gyr for a sample of 18 435 dwarf stars selected from the cross-matched Tycho-Gaia Astrometric Solution (TGAS) and RAdial Velocity Experiment (RAVE) Data Release 5. We find a correlation between the vertical metallicity gradients and age, with no vertical metallicity gradient in the youngest population and an increasingly steeper negative vertical metallicity gradient for the older stellar populations. We also find that the intrinsic dispersion in metallicity increases steadily with age. Our results are consistent with a scenario that thin disk stars formed from a flaring thin star-forming disk.

scholarly journals An automatic identification of HI shells in the 2nd and 3rd Galactic Quadrants

2006 ◽  
Vol 2 (S237) ◽  
pp. 91-95
Author(s):  
Soňa Ehlerová
Keyword(s):  
Size Distribution ◽  
Power Law ◽  
Radial Distribution ◽  
Milky Way ◽  
Hii Regions ◽  
Automatic Identification ◽  
Automatic Method ◽  
Hi Shells ◽  
Scale Length

AbstractWe briefly discuss different methods used to identify HI shells in TB datacubes. Then we give results for our automatic method applied to LDS and LAB HI surveys of the Milky Way (2nd and 3rd quadrants). We fit the radial distribution of HI shells (the exponential profile with the scale length of 3 kpc) and the size distribution (the power law with the index of 2.1). We compare the distribution of identified HI shells with HII regions and study the differences between identifications in the 2nd and 3rd quadrants.

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