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.

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 Interarm islands in the Milky Way – the one near the Cygnus spiral arm

2020 ◽  
Vol 494 (1) ◽  
pp. 1134-1142
Author(s):  
Jacques P Vallée
Keyword(s):  
Observational Data ◽  
Milky Way ◽  
Young Stars ◽  
H Ii Regions ◽  
Spiral Arms ◽  
The Galaxy ◽  
The One ◽  
Loop 2 ◽  
Perseus Arm ◽  
Spiral Arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

scholarly journals The SEDIGISM survey: the influence of spiral arms on the molecular gas distribution of the inner Milky Way

2021 ◽  
Author(s):  
D. Colombo ◽  
A. Duarte-Cabral ◽  
A. R. Pettitt ◽  
J. S. Urquhart ◽  
F. Wyrowski ◽  
...  
Keyword(s):  
Milky Way ◽  
Molecular Gas ◽  
Gas Distribution ◽  
Spiral Arms

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 6.6. The galactic bar and spiral arms

1998 ◽  
Vol 184 ◽  
pp. 273-274 ◽  
Author(s):  
O.E. Gerhard ◽  
P. Englmaier
Keyword(s):  
Surface Brightness ◽  
Light Distribution ◽  
Gas Flows ◽  
Tangent Point ◽  
Good Match ◽  
Spiral Arms ◽  
Pattern Speed ◽  
Galactic Spiral

The inner Galaxy light distribution recovered non-parametrically from the COBE/DIRBE surface brightness data shows an elongated bulge set in a highly non-axisymmetric disk. Gas flows computed in the potential of the COBE bar/bulge and disk have been compared with HI and CO line observations. For the best values of the NIR mass-to-light ratio and pattern speed a good match to the tangent point locations of the inner Galactic spiral arms is obtained.

scholarly journals Mass extinction and the structure of the milky way

2013 ◽  
pp. 43-52 ◽  
Author(s):  
M.D. Filipovic ◽  
J. Horner ◽  
E.J. Crawford ◽  
N.F.H. Tothill ◽  
G.L. White
Keyword(s):  
Mass Extinction ◽  
Milky Way ◽  
The Sun ◽  
Spiral Arms ◽  
New Model ◽  
The Galaxy ◽  
The Times ◽  
Extinction Events ◽  
Mass Extinction Events ◽  
Solar Orbit

We use the most up-to-date Milky Way model and solar orbit data in order to test the hypothesis that the Sun's galactic spiral arm crossings cause mass extinction events on Earth. To do this, we created a new model of the Milky Way's spiral arms by combining a large quantity of data from several surveys. We then combined this model with a recently derived solution for the solar orbit to determine the timing of the Sun's historical passages through the Galaxy's spiral arms. Our new model was designed with a symmetrical appearance, with the major alteration being the addition of a spur at the far side of the Galaxy. A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy's various spiral arms. Also, we briefly discuss and combine previous work on the Galactic Habitable Zone with the new Milky Way model.

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.

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 Young stars as tracers of a barred-spiral Milky Way

2019 ◽  
Author(s):  
Alex R Pettitt ◽  
Sarah E Ragan ◽  
Martin C Smith
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Young Stars ◽  
Underlying Structure ◽  
Exact Nature ◽  
Resonance Overlap ◽  
Stellar Feedback ◽  
The Galaxy ◽  
Stellar Velocity ◽  
Pattern Speed

Abstract Identifying the structure of our Galaxy has always been fraught with difficulties, and while modern surveys continue to make progress building a map of the Milky Way, there is still much to understand. The arm and bar features are important drivers in shaping the interstellar medium, but their exact nature and influence still require attention. We present results of smoothed particle hydrodynamic simulations of gas in the Milky Way including star formation, stellar feedback, and ISM cooling, when exposed to different arm and bar features, with the aim of better understanding how well newly formed stars trace out the underlying structure of the Galaxy. The bar is given a faster pattern speed than the arms, resulting in a complex, time-dependent morphology and star formation. Inter-arm branches and spurs are easily influenced by the bar, especially in the two-armed spiral models where there is a wide region of resonance overlap in the disc. As the bar over-takes the spiral arms it induces small boosts in star formation and enhances spiral features, which occur at regularly spaced beat-like intervals. The locations of star formation events are similar to those seen in observational data, and do not show a perfect 1:1 correspondence with the underlying spiral potential, though arm tangencies are generally well traced by young stars. Stellar velocity fields from the newly formed stars are compared to data from Gaia DR2, showing that the spiral and bar features can reproduce many of the non-axisymmetric features seen in the data. A simple analytical model is used to show many of these feature are a natural response of gas to rigidly rotating spiral and bar potentials.

The Long View of Planetary Systems

2018 ◽  
Author(s):  
Karel Schrijver
Keyword(s):  
Solar System ◽  
Milky Way ◽  
Planetary Systems ◽  
Giant Planets ◽  
Milky Way Galaxy ◽  
Population Statistics ◽  
The Past ◽  
General Terms ◽  
The Galaxy ◽  
The Universe

How many planetary systems formed before our’s did, and how many will form after? How old is the average exoplanet in the Galaxy? When did the earliest planets start forming? How different are the ages of terrestrial and giant planets? And, ultimately, what will the fate be of our Solar System, of the Milky Way Galaxy, and of the Universe around us? We cannot know the fate of individual exoplanets with great certainty, but based on population statistics this chapter sketches the past, present, and future of exoworlds and of our Earth in general terms.

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