scholarly journals Modelling the Galactic disc: perturbed distribution functions in the presence of spiral arms

2016 ◽  
Vol 457 (3) ◽  
pp. 2569-2582 ◽  
Author(s):  
Giacomo Monari ◽  
Benoit Famaey ◽  
Arnaud Siebert
Keyword(s):  
Distribution Functions ◽  
Galactic Disc ◽  
Spiral Arms

Distribution functions for Galactic disc stellar populations in the presence of non-axisymmetric perturbations

2017 ◽  
Vol 13 (S334) ◽  
pp. 195-198
Author(s):  
B. Famaey ◽  
G. Monari ◽  
A. Siebert ◽  
J.-B. Fouvry ◽  
J. Binney
Keyword(s):  
Stellar Population ◽  
Distribution Functions ◽  
Galactic Disc ◽  
Trapping Region ◽  
Phase Mixing ◽  
Spiral Arms ◽  
First Order ◽  
The Impact ◽  
Action Variables ◽  
Axisymmetric Perturbations

AbstractThe present-day response of a Galactic disc stellar population to a non-axisymmetric perturbation of the potential, in the form of a bar or spiral arms, can be treated, away from the main resonances, through perturbation theory within the action-angle coordinates of the unperturbed axisymmetric system. The first order moments of such a perturbed distribution function (DF) in the presence of spiral arms give rise to non-zero radial and vertical mean stellar velocities, called breathing modes. Such an Eulerian linearized treatment however diverges at resonances. The Lagrangian approach to the impact of non-axisymmetries at resonances avoids this problem. It is based on the construction of new orbital tori in the resonant trapping region, which come complete with a new system of angle-action variables. These new tori can be populated by phase-averaging the unperturbed DF over the new tori. This boils down to phase-mixing the DF in terms of the new angles, such that the DF for trapped orbits only depends on the new set of actions. This opens the way to quantitatively fitting the effects of the bar and spirals to Gaia data with an action-based DF.

scholarly journals Radial migration in a stellar galactic disc with thick components

2018 ◽  
Vol 616 ◽  
pp. A86 ◽  
Author(s):  
A. Halle ◽  
P. Di Matteo ◽  
M. Haywood ◽  
F. Combes
Keyword(s):  
Angular Momentum ◽  
Gravitational Potential ◽  
Effective Potential ◽  
Constant Speed ◽  
Galactic Disc ◽  
Spiral Arms ◽  
Radial Migration ◽  
Stellar Disc ◽  
Local Maxima ◽  
Corotation Radius

We study how radial migration affects the stars of a galaxy with a thin stellar disc and thicker stellar components. The simulated galaxy has a strong bar and lasting spiral arms. We find that the amplitude of the churning (change in angular momentum) is similar for thin and thick components, and of limited amplitude, and that stars of all components can be trapped at the corotation of the bar. With the exception of those stars trapped at the corotation, we find that stars far from their initial guiding radius are more likely to be so due to blurring rather than churning effects. We compare the simulation to orbits integration with a fixed gravitational potential rotating at a constant speed. In the latter case, stars trapped at corotation are churned periodically outside and inside the corotation radius, with a zero net average. However, as the bar speed of the simulated galaxy decreases and its corotation radius increases, stars trapped at corotation for several Gyrs can be churned on average outwards. In this work we have studied the location of extreme migrators (stars experimenting the largest churning) and find that extreme migrators come from regions on the leading side of the effective potential local maxima.

scholarly journals Distribution functions for resonantly trapped orbits in the Galactic disc

2017 ◽  
Vol 471 (4) ◽  
pp. 4314-4322 ◽  
Author(s):  
Giacomo Monari ◽  
Benoit Famaey ◽  
Jean-Baptiste Fouvry ◽  
James Binney
Keyword(s):  
Distribution Functions ◽  
Galactic Disc

scholarly journals Perturbed distribution functions with accurate action estimates for the Galactic disc

2021 ◽  
Author(s):  
H. Al Kazwini ◽  
Q. Agobert ◽  
A. Siebert ◽  
B. Famaey ◽  
G. Monari ◽  
...  
Keyword(s):  
Distribution Functions ◽  
Galactic Disc

scholarly journals Molecular clouds: comet factories?

1985 ◽  
Vol 83 ◽  
pp. 19-30
Author(s):  
S.V.M. Clube
Keyword(s):  
Solar System ◽  
Molecular Clouds ◽  
Oort Cloud ◽  
Number Density ◽  
Galactic Disc ◽  
Precursor State ◽  
Spiral Arms ◽  
Isotopic Signatures ◽  
History Of

AbstractRecent discoveries seem to indicate a catastrophic history of terrestrial evolution, explicable in terms of Oort cloud disturbance by molecular clouds in the Galactic disc. The problem of Oort cloud replenishment thus assumes considerable significance and reasons are given for supposing comet exchange takes place during actual penetration of molecular clouds. The number density of comets in molecular clouds, thereby implied, seems to suggest primary condensations of ≤103km in a dense precursor state of spiral arms. If chemical and/or isotopic signatures of comets should indicate an extra-Solar System source, the theory of terrestrial catastrophism may place new constraints on our understanding of the origin of molecular clouds.

scholarly journals Imprints of spiral arms in the oxygen distribution over the galactic disc

2005 ◽  
Vol 359 (3) ◽  
pp. 819-826 ◽  
Author(s):  
I. A. Acharova ◽  
J. R. D. Lépine ◽  
Yu. N. Mishurov
Keyword(s):  
Oxygen Distribution ◽  
Galactic Disc ◽  
Spiral Arms

scholarly journals SEDIGISM-ATLASGAL: dense gas fraction and star formation efficiency across the Galactic disc

2020 ◽  
Vol 500 (3) ◽  
pp. 3050-3063 ◽  
Author(s):  
J S Urquhart ◽  
C Figura ◽  
J R Cross ◽  
M R A Wells ◽  
T J T Moore ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Fraction ◽  
Local Environment ◽  
Cloud Formation ◽  
Physical Parameters ◽  
Dense Gas ◽  
Galactic Disc ◽  
Large Area ◽  
Spiral Arms ◽  
Molecular Material

ABSTRACT By combining two surveys covering a large fraction of the molecular material in the Galactic disc, we investigate the role spiral arms play in the star formation process. We have matched clumps identified by APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) with their parental giant molecular clouds (GMCs) as identified by SEDIGISM, and use these GMC masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (DGFgmc = ∑Mclump/Mgmc) and the instantaneous star formation efficiencies (i.e. SFEgmc = ∑Lclump/Mgmc). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms (∼60 per cent found within ±10 $\rm {km\,s}^{-1}$ of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and H i to H2 conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of any physical process.

Distribution functions for resonantly trapped orbits in our Galaxy

2017 ◽  
Vol 13 (S334) ◽  
pp. 341-342
Author(s):  
G. Monari ◽  
B. Famaey ◽  
J.-B. Fouvry ◽  
J. Binney
Keyword(s):  
Distribution Function ◽  
Phase Space ◽  
Stellar Population ◽  
Distribution Functions ◽  
Space Distribution ◽  
Galactic Disc ◽  
Phase Mixing ◽  
Phase Space Distribution ◽  
Resonant Region ◽  
Time Average

AbstractWe show how to capture the behaviour of the phase-space distribution function (DF) of a Galactic disc stellar population at a resonance. This is done by averaging the Hamiltonian over fast angle variables and re-expressing the DF in terms of a new set of canonical actions and angles variables valid in the resonant region. We then assign to the resonant DF the time average along the orbits of the axisymmetric DF expressed in the new set of actions and angles. This boils down to phase-mixing the DF in terms of the new angles, such that the DF for trapped orbits only depends on the new set of actions. This opens the way to quantitatively fitting the effects of the bar and spirals to Gaia data in terms of distribution functions in action space.

Computer processing of high-resolution images of periodic specimens

1986 ◽  
Vol 44 ◽  
pp. 2-5
Author(s):  
W. Chiu ◽  
M.F. Schmid ◽  
T.-W. Jeng
Keyword(s):  
High Resolution ◽  
Fourier Transforms ◽  
Complex Structure ◽  
Distribution Functions ◽  
Multiple Image ◽  
Cryo Electron Microscopy ◽  
Structure Factors ◽  
Unit Cells ◽  
High Resolution Images ◽  
Phase Probability Distribution

Cryo-electron microscopy has been developed to the point where one can image thin protein crystals to 3.5 Å resolution. In our study of the crotoxin complex crystal, we can confirm this structural resolution from optical diffractograms of the low dose images. To retrieve high resolution phases from images, we have to include as many unit cells as possible in order to detect the weak signals in the Fourier transforms of the image. Hayward and Stroud proposed to superimpose multiple image areas by combining phase probability distribution functions for each reflection. The reliability of their phase determination was evaluated in terms of a crystallographic “figure of merit”. Grant and co-workers used a different procedure to enhance the signals from multiple image areas by vector summation of the complex structure factors in reciprocal space.

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