scholarly journals A secularly evolved model for the Milky Way bar and bulge

2012 ◽  
Vol 10 (H16) ◽  
pp. 351-351 ◽  
Author(s):  
Inma Martinez-Valpuesta ◽  
Ortwin Gerhard
Keyword(s):  
Milky Way ◽  
Momentum Transport ◽  
Disk Galaxies ◽  
Kinematic Data ◽  
Angular Momentum Transport ◽  
Secular Evolution ◽  
Upper Limit ◽  
Self Consistent ◽  
The Galaxy ◽  
Pattern Speed

AbstractBars are strong drivers of secular evolution in disk galaxies. Bars themselves can evolve secularly through angular momentum transport, producing different boxy/peanut and X-shaped bulges. Our Milky Way is an example of a barred galaxy with a boxy bulge. We present a self-consistent N-body simulation of a barred galaxy which matches remarkably well the structure of the inner Milky Way deduced from star counts. In particular, features taken as signatures of a second “long bar“ can be explained by the interaction between the bar and the spiral arms of the galaxy (Martinez-Valpuesta & Gerhard 2011). Furthermore the structural change in the bulge inside l = 4° measured recently from VVV data can be explained by the high-density near-axisymmetric part of the inner boxy bulge (Gerhard & Martinez-Valpuesta 2012). We also compare this model with kinematic data from recent spectroscopic surveys. We use a modified version of the NMAGIC code (de Lorenzi et al. 2007) to study the properties of the Milky Way bar, obtaining an upper limit for the pattern speed of ~ 42 km/sec/kpc. See Fig. 1 for a comparison of one of our best models with BRAVA data (Kunder et al. 2012).

scholarly journals Simulation of Mass Transport in Disk Galaxies

1996 ◽  
Vol 171 ◽  
pp. 405-405 ◽  
Author(s):  
S. von Linden ◽  
J. Heidt ◽  
H.P. Reuter ◽  
R. Wielebinski
Keyword(s):  
Angular Momentum ◽  
Mass Transport ◽  
Large Scale ◽  
Momentum Transport ◽  
Disk Galaxies ◽  
Angular Momentum Transport ◽  
Gravitational Instabilities ◽  
Gas Component

The large-scale dynamics and evolution of disk galaxies is controlled by the angular-momentum transport provided by non-axisymmetric perturbances through their gravity torques. To continuously maintain such gravitational instabilities, the presence of the gas component and its dissipative character are essential.

scholarly journals First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation

2019 ◽  
Vol 631 ◽  
pp. A77 ◽  
Author(s):  
L. Amard ◽  
A. Palacios ◽  
C. Charbonnel ◽  
F. Gallet ◽  
C. Georgy ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Open Clusters ◽  
Momentum Transport ◽  
Surface Boundary ◽  
Angular Momentum Transport ◽  
Solar Composition ◽  
Self Consistent ◽  
Low Mass ◽  
Stellar Models ◽  
The Impact

Aims.We present an extended grid of state-of-the art stellar models for low-mass stars including updated physics (nuclear reaction rates, surface boundary condition, mass-loss rate, angular momentum transport, rotation-induced mixing, and torque prescriptions). We evaluate the impact of wind braking, realistic atmospheric treatment, rotation, and rotation-induced mixing on the structural and rotational evolution from the pre-main sequence (PMS) to the turn-off.Methods.Using the STAREVOL code, we provide an updated PMS grid. We computed stellar models for seven different metallicities, from [Fe/H] = −1 dex to [Fe/H] = +0.3 dex with a solar composition corresponding toZ = 0.0134. The initial stellar mass ranges from 0.2 to 1.5M⊙with extra grid refinement around one solar mass. We also provide rotating models for three different initial rotation rates (slow, median, and fast) with prescriptions for the wind braking and disc-coupling timescale calibrated on observed properties of young open clusters. The rotational mixing includes the most recent description of the turbulence anisotropy in stably stratified regions.Results.The overall behaviour of our models at solar metallicity, and their constitutive physics, are validated through a detailed comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over a wide range of mass values. These models are publicly available and can be used to analyse data coming from present and forthcoming asteroseismic and spectroscopic surveys such asGaia, TESS, and PLATO.

scholarly journals From manifolds to Lagrangian coherent structures in galactic bar models

2018 ◽  
Vol 618 ◽  
pp. A72 ◽  
Author(s):  
P. Sánchez-Martín ◽  
J. J. Masdemont ◽  
M. Romero-Gómez
Keyword(s):  
Dynamical System ◽  
Fluid Dynamics ◽  
Coherent Structures ◽  
Invariant Manifolds ◽  
Lagrangian Coherent Structures ◽  
Galactic Dynamics ◽  
Secular Evolution ◽  
Autonomous Case ◽  
The Galaxy ◽  
Pattern Speed

We study the dynamics near the unstable Lagrangian points in galactic bar models using dynamical system tools in order to determine the global morphology of a barred galaxy. We aim at the case of non-autonomous models, in particular with secular evolution, by allowing the bar pattern speed to decrease with time. We have extended the concept of manifolds widely used in the autonomous problem to the Lagrangian coherent structures (LCS), widely used in fluid dynamics, which behave similar to the invariant manifolds driving the motion. After adapting the LCS computation code to the galactic dynamics problem, we apply it to both the autonomous and non-autonomous problems, relating the results with the manifolds and identifying the objects that best describe the motion in the non-autonomous case. We see that the strainlines coincide with the first intersection of the stable manifold when applied to the autonomous case, while, when the secular model is used, the strainlines still show the regions of maximal repulsion associated to both the corresponding stable manifolds and regions with a steep change of energy. The global morphology of the galaxy predicted by the autonomous problem remains unchanged.

scholarly journals Searching for observational evidence of radial mixing in the Milky Way disk

2012 ◽  
Vol 10 (H16) ◽  
pp. 356-356
Author(s):  
Misha Haywood
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Theoretical Studies ◽  
Secular Evolution ◽  
Chemical Gradients ◽  
Current State ◽  
The Galaxy ◽  
The Subject ◽  
The Mean ◽  
State Of Affairs

AbstractSecular evolution in disks through angular momentum redistribution of stars induce radial mixing of their orbits. While theoretical studies and simulations now abound on the subject - with various predicted effects: disks growth, flattening of metallicity gradients, possible reversing of the mean age as a function of radius in disk, etc, observational evidences remain sparse. In the Galaxy, possible signatures are searched for in the local distributions of velocities, abundances and ages, or in the variation of large scale chemical gradients with time. I will present the current state of affairs and discuss what kind of evidences is available from data in the Milky Way.

scholarly journals Resolving the stellar outskirts of six Milky Way-like galaxies beyond the Local Group

2016 ◽  
Vol 11 (S321) ◽  
pp. 43-43
Author(s):  
A. Monachesi ◽  
E. F. Bell ◽  
D. J. Radburn-Smith ◽  
B. Harmsen ◽  
R. S. de Jong ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Milky Way ◽  
Local Group ◽  
Spiral Galaxies ◽  
Disk Galaxies ◽  
Galaxy Halos ◽  
Model Predictions ◽  
The Galaxy ◽  
Thick Disks ◽  
Stellar Properties

AbstractModels of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies’ merger histories. Currently, only few detailed observations of galaxy’s halos are available, mainly for the Milky Way and M31. The Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey is the largest study to date of the resolved stellar populations in the outskirts of disk galaxies and its observations offer a direct test of model predictions. Here we present the results we obtain for six highly inclined nearby Milky Way-mass spiral galaxies. We find a great diversity in the properties of their stellar halos.

The galactic habitable zone in barred galaxies

2006 ◽  
Vol 5 (4) ◽  
pp. 325-326 ◽  
Author(s):  
M. Sundin
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Habitable Zone ◽  
Escape Velocity ◽  
Stellar Orbits ◽  
Barred Galaxies ◽  
The Galaxy ◽  
Pattern Speed ◽  
Disc Galaxies ◽  
High Metallicity

One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to define since the bar can change stellar orbits. Many disc galaxies, including the Milky Way, are barred galaxies. The stars in the bar move in a number of fairly complicated orbits. However, the bar will also influence the orbits of stars in the whole galaxy. Stars passing close to the bar can either gain or lose angular momentum, due to a positive or negative torque by the bar. Some stars will therefore be captured by the bar while some stars eventually may reach the escape velocity from the galaxy. The bar will hence be able to relocate stars, and stars with low or high metallicity could be found far away from their original orbits. The ordinary evolution of a bar is to grow in length out to the co-rotation radius for the pattern speed of the bar. As the galaxy ages, and the bar grows in length, the bar will influence a larger part of the galaxy. The effect of moving stars inwards or outwards is greatest just outside the bar, and this region can eventually lose a high percentage of the stars.

scholarly journals Rotation of classical bulges during secular evolution of barred galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 329-329
Author(s):  
Kanak Saha ◽  
Ortwin Gerhard
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Disk Galaxies ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Low Mass ◽  
Fast Rotating

AbstractBar driven secular evolution plays a key role in changing the morphology and kinematics of disk galaxies, leading to the formation of rapidly rotating boxy/peanut bulges. If these disk galaxies also hosted a preexisting classical bulge, how would the secular evolution influence the classical bulge, and also the observational properties.We first study the co-evolution of a bar and a preexisting non-rotating low-mass classical bulge such as might be present in galaxies like the Milky Way. It is shown with N-body simulations that during the secular evolution, such a bulge can gain significant angular momentum emitted by the bar through resonant and stochastic orbits. Thereby it transforms into a cylindrically rotating, anisotropic and triaxial object, embedded in the fast rotating boxy bulge that forms via disk instability (Saha et al. 2012). The composite boxy/peanut bulge also rotates cylindrically.We then show that the growth of the bar depends only slightly on the rotation properties of the preexisting classical bulge. For the initially rotating small classical bulge, cylindrical rotation in the resulting composite boxy/peanut bulge extends to lower heights (Saha & Gerhard 2013). More massive classical bulges also gain angular momentum emitted by the bar, inducing surprisingly large rotational support within about 4 Gyrs (Saha et al. in prep).

scholarly journals Gas flows within the Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 186-187
Author(s):  
Francoise Combes
Keyword(s):  
Milky Way ◽  
Gas Flows ◽  
Gas Distribution ◽  
Spiral Arms ◽  
The Galaxy ◽  
Pattern Speed ◽  
Solar Position ◽  
New Discovery

AbstractIn the recent years, more and more sophisticated models have been proposed for the gas distribution and kinematics in the Milky Way, taking into account the main bar, but also the possible nuclear bar, with the same or different pattern-speed. I review the success and problems encountered by the models, in particular in view of the new discovery of a symmetrical far-side counterpart of the 3 kpc arm. The inner part, dominated by the bar, and the outer parts, dominated by the spiral arms, can be observed from a virtual solar position, and the errors coming from kinematical distances are evaluated. The appearance of four arms could be due to a deprojection bias.

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