scholarly journals Constraining the pitch angle of the galactic spiral arms in the Milky Way

2017 ◽  
Vol 79 ◽  
pp. 49-58 ◽  
Author(s):  
Jacques P. Vallée
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Arms ◽  
Galactic Spiral

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 Can we detect Galactic spiral arms? 3D dust distribution in the Milky Way

2017 ◽  
Vol 12 (S330) ◽  
pp. 189-192 ◽  
Author(s):  
Sara Rezaei Kh. ◽  
Coryn A. L. Bailer-Jones ◽  
Morgan Fouesneau ◽  
Richard Hanson
Keyword(s):  
Spatial Correlation ◽  
High Precision ◽  
Milky Way ◽  
Precision Measurements ◽  
Line Of Sight ◽  
Spiral Arms ◽  
Dust Extinction ◽  
The Galaxy ◽  
Galactic Spiral ◽  
Dust Distribution

AbstractWe present a model to map the 3D distribution of dust in the Milky Way. Although dust is just a tiny fraction of what comprises the Galaxy, it plays an important role in various processes. In recent years various maps of dust extinction have been produced, but we still lack a good knowledge of the dust distribution. Our presented approach leverages line-of-sight extinctions towards stars in the Galaxy at measured distances. Since extinction is proportional to the integral of the dust density towards a given star, it is possible to reconstruct the 3D distribution of dust by combining many lines-of-sight in a model accounting for the spatial correlation of the dust. Such a technique can be used to infer the most probable 3D distribution of dust in the Galaxy even in regions which have not been observed. This contribution provides one of the first maps which does not show the “fingers of God” effect. Furthermore, we show that expected high precision measurements of distances and extinctions offer the possibility of mapping the spiral arms in the Galaxy.

scholarly journals Using synthetic emission maps to constrain the structure of the Milky Way

2013 ◽  
Vol 9 (S298) ◽  
pp. 246-252 ◽  
Author(s):  
Alex R. Pettitt ◽  
Clare L. Dobbs ◽  
David M. Acreman ◽  
Daniel J. Price
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Arms ◽  
The Earth ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Pattern Speeds ◽  
Best Fit ◽  
Grid Based ◽  
Key Questions

AbstractWe present the current standing of an investigation into the structure of the Milky Way. We use smoothed particle hydrodynamics (SPH) to simulate the ISM gas in the Milky Way under the effect of a number of different gravitational potentials representing the spiral arms and nuclear bars, both fixed and time-dependent. The gas is subject to ISM cooling and chemistry, enabling us to track the CO and HI density. We use a 3D grid-based radiative transfer code to simulate the emission from the SPH output, allowing for the construction of synthetic longitude-velocity maps as viewed from the Earth. By comparing these maps with the observed emission in CO and HI from the Milky Way ([Dame et al. 2001, Kalberla et al. 2005]), we can infer the arm/bar geometry that provides a best fit to our Galaxy. By doing so we aim to answer key questions concerning the morphology of the Milky Way such as the number of the spiral arms, the pattern speeds of the bar(s) and arms, the pitch angle of the arms and shape of the bar(s).

scholarly journals SYNERGY BETWEEN OPTICAL (GAIA) AND RADIO (VLBI)ASTROMETRIC RESEARCHES

2020 ◽  
Vol 52 ◽  
pp. 9-11
Author(s):  
N. Sakai
Keyword(s):  
Spatial Distribution ◽  
Milky Way ◽  
Spiral Arms ◽  
Multi Wavelength ◽  
Complex Picture ◽  
Galactic Spiral

Optical and radio astrometry have become significant for mapping the Milky Way. We introduce an example of synergy between optical and radio astrometry on a research of the Galactic spiral arms. Kinematics and spatial distribution of star and gas indicate a new and complex picture of the Galactic spiral arms. Synergy of astrometric study at multi-wavelength would be enhanced thanks to future infrared astrometric projects (e.g.,Small Jasmine; GaiaNIR) in 2020-2030s.

Progress on 21 cm Studies of the Southern Milky Way _

1975 ◽  
Vol 2 (6) ◽  
pp. 364-365 ◽  
Author(s):  
F.J. Kerr
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Radial Velocities ◽  
Straightforward Manner ◽  
Spiral Arms ◽  
Distance Transformation ◽  
Galactic Spiral Structure ◽  
Structure Problem ◽  
Galactic Spiral

In the first decade or so of 21 cm studies the galactic spiral structure problem was treated in a very straightforward manner. A simple velocity-distance transformation was used to derive the locations of the spiral arms from the radial velocities of the main features on the 21 cm profiles. Some well-known diagrams were obtained in this way.

scholarly journals PITCH ANGLE OF GALACTIC SPIRAL ARMS

2014 ◽  
Vol 787 (2) ◽  
pp. 174 ◽  
Author(s):  
Shugo Michikoshi ◽  
Eiichiro Kokubo
Keyword(s):  
Pitch Angle ◽  
Spiral Arms ◽  
Galactic Spiral

scholarly journals Spatial and velocity offsets of Galactic masers from the centres of spiral arms

2019 ◽  
Vol 489 (2) ◽  
pp. 2819-2829 ◽  
Author(s):  
Jacques P Vallée
Keyword(s):  
Star Formation ◽  
Pitch Angle ◽  
Milky Way ◽  
Galactic Centre ◽  
Spiral Arms ◽  
Corotation Radius ◽  
Pattern Speed ◽  
Spiral Model ◽  
Spiral Arm ◽  
Co Gas

ABSTRACT Some theories about the spiral arms of galaxies predict an offset between different tracers of star formation. Our goal in this paper is to find such an offset between the observed locations of radio masers and the locations of the arms, using a recent four-arm model fitted to the CO 1–0 gas. Our method is to compare a recent global four-arm spiral model (as fitted to the arms’ tangents in the observed broad CO 1–0 gas) with the recent results for the trigonometric distances of radio masers, for the main arms (Cygnus–Norma, Perseus, Sagittarius–Carina, Scutum and Norma). Our results indicate that most radio masers are near the inner edge of each spiral arm (towards the Galactic Centre). These masers are offset from the model arm (where the broad CO 1–0 molecular region resides), by 0.34 ± 0.06 kpc inward. In radial velocity space, the median offset between masers and the CO-fitted model is around 10 ± 1 km s–1. Based on the fact that the masers are observed here to be radially inward of the broad CO gas in the Cygnus arm at 15 kpc along the Galactic meridian, the corotation radius of the Milky Way disc is >15 kpc distant from the Galactic Centre and the density wave’s angular pattern speed is <15 km s–1 kpc–1. The pitch angle of the arm should be measured using many arm tracers, and located on both sides of the Galactic meridian, to ensure better precision and to avoid a bias pertinent to a single tracer.

scholarly journals Kinematics of symmetric Galactic longitudes to probe the spiral arms of the Milky Way withGaia

2016 ◽  
Vol 589 ◽  
pp. A13 ◽  
Author(s):  
T. Antoja ◽  
S. Roca-Fàbrega ◽  
J. de Bruijne ◽  
T. Prusti
Keyword(s):  
Milky Way ◽  
Spiral Arms

scholarly journals Autonomous Gaussian decomposition of the Galactic Ring Survey

2020 ◽  
Vol 640 ◽  
pp. A72
Author(s):  
M. Riener ◽  
J. Kainulainen ◽  
J. D. Henshaw ◽  
H. Beuther
Keyword(s):  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Plane ◽  
Gas Emission ◽  
Spiral Arms ◽  
Precise Knowledge ◽  
Significant Difference ◽  
The Impact ◽  
Co Emission ◽  
Spiral Arm

Knowledge about the distribution of CO emission in the Milky Way is essential to understanding the impact of the Galactic environment on the formation and evolution of structures in the interstellar medium. However, our current insight as to the fraction of CO in the spiral arm and interarm regions is still limited by large uncertainties in assumed rotation curve models or distance determination techniques. In this work we use the Bayesian approach from Reid et al. (2016, ApJ, 823, 77; 2019, ApJ, 885, 131), which is based on our most precise knowledge at present about the structure and kinematics of the Milky Way, to obtain the current best assessment of the Galactic distribution of 13CO from the Galactic Ring Survey. We performed two different distance estimates that either included (Run A) or excluded (Run B) a model for Galactic features, such as spiral arms or spurs. We also included a prior for the solution of the kinematic distance ambiguity that was determined from a compilation of literature distances and an assumed size-linewidth relationship. Even though the two distance runs show strong differences due to the prior for Galactic features for Run A and larger uncertainties due to kinematic distances in Run B, the majority of their distance results are consistent with each other within the uncertainties. We find that the fraction of 13CO emission associated with spiral arm features ranges from 76 to 84% between the two distance runs. The vertical distribution of the gas is concentrated around the Galactic midplane, showing full-width at half-maximum values of ~75 pc. We do not find any significant difference between gas emission properties associated with spiral arm and interarm features. In particular, the distribution of velocity dispersion values of gas emission in spurs and spiral arms is very similar. We detect a trend of higher velocity dispersion values with increasing heliocentric distance, which we, however, attribute to beam averaging effects caused by differences in spatial resolution. We argue that the true distribution of the gas emission is likely more similar to a combination of the two distance results discussed, and we highlight the importance of using complementary distance estimations to safeguard against the pitfalls of any single approach. We conclude that the methodology presented in this work is a promising way to determine distances to gas emission features in Galactic plane surveys.

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