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 The Dynamics of the Galactic Bar

1996 ◽  
Vol 157 ◽  
pp. 516-528
Author(s):  
Martin D. Weinberg
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Field Pattern ◽  
Barred Galaxies ◽  
The Galaxy ◽  
Data Volume ◽  
Alternative Hypotheses ◽  
Formation And Evolution ◽  
Evolution Of Structure ◽  
Pattern Speeds

The dynamics of formation and evolution of structure in barred galaxies is subtle and will require many and detailed observations to discriminate between the alternative hypotheses. Why should someone interested in such problems consider the Milky Way? In terms of data volume, our knowledge of the Milky Way is vast and the availability of detail is its major advantage. In principle, one can study morphological details such as orientations, strengths of asymmetries and kinematics details such as velocity field/pattern speeds using a wide variety of tracers. To illustrate, theorists have not converged on a single mechanism to explain bars (witness the instability vs. secular formation debate). It is possible that both operate in different regimes depending on internal or external influences: internally, triaxialities and misalignments in the bulge, spheroid or halo can apply torques and drive angular momentum waves which saturate to form a bar; and externally, satellite galaxies can exchange orbital angular momentum with its disturbance which has the similar effect. In short, if the Galaxy is indeed barred, it may hold clues to some of the detailed problems posed at this meeting.

scholarly journals Bars and the connection between dark and visible matter

2004 ◽  
Vol 220 ◽  
pp. 255-264 ◽  
Author(s):  
E. Athanassoula
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Barred Galaxies ◽  
Visible Matter ◽  
Pattern Speed ◽  
Disc Galaxies

Isolated barred galaxies evolve by redistributing their internal angular momentum, which is emitted mainly at the inner disc resonances and absorbed mainly at the resonances in the outer disc and the halo. This causes the bar to grow stronger and its pattern speed to decrease with time. A massive, responsive halo enhances this process. I show correlations and trends between the angular momentum absorbed by the halo and the bar strength, pattern speed and morphology. It is thus possible to explain why some disc galaxies are strongly barred, while others have no bar, or only a short bar or an oval. in some cases, a bar is found also in the halo component. This “halo bar” is triaxial, but more prolate-like, is shorter than the disc bar and rotates with roughly the same pattern speed. I finally discuss whether bars can modify the density cusps found in cosmological CDM simulations of dark matter haloes.

scholarly journals Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

2020 ◽  
Author(s):  
Bogdan C Ciambur ◽  
Francesca Fragkoudi ◽  
Sergey Khoperskov ◽  
Paola Di Matteo ◽  
Françoise Combes
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Large Fraction ◽  
Formation Time ◽  
Dark Matter Halo ◽  
Barred Galaxies ◽  
Pattern Speed ◽  
Nearby Galaxies ◽  
Dynamical Instabilities ◽  
Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

scholarly journals On a mechanism that structures galaxies

1979 ◽  
Vol 84 ◽  
pp. 157-158
Author(s):  
D. Lynden-Bell
Keyword(s):  
Angular Momentum ◽  
Differential Rotation ◽  
Spiral Structure ◽  
Rotation Curves ◽  
Eccentric Orbits ◽  
The Galaxy ◽  
Central Regions ◽  
Pattern Speed ◽  
Stellar Orbit ◽  
Lindblad Resonance

By considering the interaction of a single stellar orbit with a weak cos 2Φ potential it is shown that in the central regions of galaxies with slowly rising rotation curves, the elongations of the orbits will align along any potential valley and oscillate about it. This effect is more pronounced for elongated orbits. In such regions any pair of orbits will naturally align under their mutual gravity and so a bar will form. The gravity of this bar will drive a spiral structure in the outer parts of the galaxy where differential rotation is too strong to allow the orbits to be caught by the bar. The spiral structure carries a torque which slowly drains angular momentum from the bar, gradually making its outline more eccentric and slowing its pattern speed. In the outer parts of the bar only the more eccentric orbits align with the potential valley; the rounder ones form a ring or lens about the bar. As the pattern speed slows down, the corotation resonance and outer Lindblad resonance, which receive the angular momentun, move outwards. The evolution of the system is eventually slowed down by the weakness of these outer resonances where the material is rather sparse.

scholarly journals Mass of the Milky Way

2004 ◽  
Vol 220 ◽  
pp. 213-214
Author(s):  
O. I. Wong ◽  
M. J. Drinkwater ◽  
J. B. Jones ◽  
M. D. Gregg ◽  
K. C. Freeman
Keyword(s):  
Milky Way ◽  
Galactic Centre ◽  
Escape Velocity ◽  
The Galaxy

We present a new estimate of the mass of the Milky Way based on the escape velocity of a sample of distant stars, about 12 kpc from the Galactic centre and about 5 kpc from the plane of the Galaxy. Our sample is very different from previous escape-velocity studies, being compiled from an all-object spectroscopic survey of a region of sky. the derived mass within 12 kpc of the Galactic centre is (1.3 ±0.3) × 1011M⊙.

scholarly journals The Bulge-disc connection in the Milky Way

2008 ◽  
Vol 4 (S254) ◽  
pp. 145-152
Author(s):  
James Binney
Keyword(s):  
Angular Momentum ◽  
Stellar Population ◽  
Milky Way ◽  
Dark Halo ◽  
Principal Characteristics ◽  
Corotation Radius ◽  
The Galaxy

AbstractBulges come in two flavours – classical and pseudo. The principal characteristics of each flavour are summarised and their impact on discs is considered. Classical bulges probably inhibit the formation of stellar discs. Pseudobulges exchange angular momentum with stars and gas in their companion discs, and also with its embedding dark halo. Since the structure of a pseudobulge depends critically on its angular momentum, these exchanges are expected to modify the bulge. The consequences of this modification are not yet satisfactorily understood. The Galaxy has a pseudobulge. I review the manifestations of its interaction with the disc. More work is needed on the dynamics of gas near the bulge's corotation radius, and on tracing the stellar population in the inner few hundred parsecs of the Galaxy.

scholarly journals Revealing galactic scale bars with the help of Galaxy Zoo

2012 ◽  
Vol 10 (H16) ◽  
pp. 324-324
Author(s):  
Karen L. Masters ◽  
Keyword(s):  
Stellar Mass ◽  
Sloan Digital Sky Survey ◽  
Gas Content ◽  
Barred Galaxies ◽  
Sky Survey ◽  
The Galaxy ◽  
Galaxy Sample ◽  
External Sources ◽  
Disc Galaxies ◽  
Environmental Dependence

AbstractWe use visual classifications of the brightest 250,000 galaxies in the Sloan Digital Sky Survey Main Galaxy Sample provided by citizen scientists via the Galaxy Zoo project (www.galaxyzoo.org, Lintott et al. 2008) to identify a sample of local disc galaxies with reliable bar identifications.These data, combined with information on the atomic gas content from the ALFALFA survey (Haynes et al. 2011) show that disc galaxies with higher gas content have lower bar fractions.We use a gas deficiency parameter to show that disc galaxies with more/less gas than expected for their stellar mass are less/more likely to host bars. Furthermore, we see that at a fixed gas content there is no residual correlation between bar fraction and stellar mass. We argue that this suggests previously observed correlations between galaxy colour/stellar mass and (strong) bar fraction (e.g. from the sample in Masters et al. 2011, and also see Nair & Abraham 2010) could be driven by the interaction between bars and the gas content of the disc, since more massive, optically redder disc galaxies are observed to have lower gas contents.Furthermore we see evidence that at a fixed gas content the global colours of barred galaxies are redder than those of unbarred galaxies. We suggest that this could be due to the exchange of angular momentum beyond co-rotation which might stop a replenishment of gas from external sources, and act as a source of feedback to temporarily halt or reduce the star formation in the outer parts of barred discs.These results (published as Masters et al. 2012) combined with those of Skibba et al. (2012), who use the same sample to show a clear (but subtle and complicated) environmental dependence of the bar fraction in disc galaxies, suggest that bars are intimately linked to the evolution of disc galaxies.

scholarly journals Galactic spiral structure

2009 ◽  
Vol 465 (2111) ◽  
pp. 3425-3446 ◽  
Author(s):  
Charles Francis ◽  
Erik Anderson
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Stellar Orbits ◽  
Grand Design ◽  
Galactic Spiral Structure ◽  
Pattern Speed ◽  
Galactic Spiral ◽  
Almost All ◽  
Spiral Arm

We describe the structure and composition of six major stellar streams in a population of 20 574 local stars in the New Hipparcos Reduction with known radial velocities. We find that, once fast moving stars are excluded, almost all stars belong to one of these streams. The results of our investigation have led us to re-examine the hydrogen maps of the Milky Way, from which we identify the possibility of a symmetric two-armed spiral with half the conventionally accepted pitch angle. We describe a model of spiral arm motions that matches the observed velocities and compositions of the six major streams, as well as the observed velocities of the Hyades and Praesepe clusters at the extreme of the Hyades stream. We model stellar orbits as perturbed ellipses aligned at a focus in coordinates rotating at the rate of precession of apocentre. Stars join a spiral arm just before apocentre, follow the arm for more than half an orbit, and leave the arm soon after pericentre. Spiral pattern speed equals the mean rate of precession of apocentre. Spiral arms are shown to be stable configurations of stellar orbits, up to the formation of a bar and/or ring. Pitch angle is directly related to the distribution of orbital eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve to form bars and rings. We show that orbits of gas clouds are stable only in bisymmetric spirals. We conclude that spiral galaxies evolve toward grand design two-armed spirals. We infer from the velocity distributions that the Milky Way evolved into this form about 9 billion years ago (Ga).

scholarly journals Helium abundances and its radial gradient from the spectra of H ii regions and ring nebulae of the Milky Way

2020 ◽  
Vol 496 (3) ◽  
pp. 2726-2742 ◽  
Author(s):  
J E Méndez-Delgado ◽  
C Esteban ◽  
J García-Rojas ◽  
K Z Arellano-Córdova ◽  
M Valerdi
Keyword(s):  
Milky Way ◽  
H Ii Regions ◽  
Abundance Gradient ◽  
Radial Gradient ◽  
Physical Conditions ◽  
The Galaxy ◽  
Ring Nebulae ◽  
Gaia Dr2 ◽  
Disc Galaxies ◽  
Weakly Dependent

ABSTRACT We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 H ii regions and ring nebulae surrounding massive O-type stars. We revise the Galactocentric distances of the objects considering Gaia DR2 parallaxes (Gaia Collaboration 2018) and determine the physical conditions and the ionic abundance of He+ in a homogeneous way, using between 3 and 10 He i recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ionization correction factor (ICF; He) schemes. The slope of the gradient is always negative and weakly dependent on the ICF(He) scheme, especially when only the objects with log(η) < 0.9 are considered. The slope values go from −0.0078 to −0.0044 dex kpc−1, consistent with the predictions of chemical evolution models of the Milky Way and chemodynamical simulations of disc galaxies. Finally, we estimate the abundance deviations of He, O, and N in a sample of ring nebulae around Galactic Wolf–Rayet stars, finding a quite similar He overabundance of about +0.24 ± 0.11 dex in three stellar ejecta ring nebulae.

NIHAO-UHD: High-resolution Simulations of MW mass galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 209-212
Author(s):  
Tobias Buck ◽  
Andrea Macciò ◽  
Melissa Ness ◽  
Aura Obreja ◽  
Aaron Dutton
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Satellite System ◽  
The Galaxy ◽  
First Results ◽  
History Of ◽  
Galaxy Center ◽  
Hydrodynamical Simulations ◽  
Very High ◽  
Disc Galaxies

AbstractHigh resolution cosmological and hydrodynamical simulations have reached a resolution able to resolve in a self consistent way the disc of our galaxy, the galaxy center and the satellites orbiting around it. We present first results from the NIHAO-UHD project, a set of very high-resolution baryonic zoom-in simulations of Milky Way mass disc galaxies. These simulations model the full cosmological assembly history of the galaxies and their satellite system using the same, well tested physics as the NIHAO project. We show that these simulations can self-consistently reproduce the observed kinematical and morphological features of the X-shaped bulge observed in our own Milky Way.

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