scholarly journals Are there Giant Vortices near Solar Circle?

1996 ◽  
Vol 169 ◽  
pp. 597-604
Author(s):  
A.M. Fridman ◽  
O.V. Khoruzhii ◽  
V.V. Lyakhovich ◽  
V.S. Avedisova
Keyword(s):  
Velocity Field ◽  
Radial Velocity ◽  
Observational Data ◽  
Molecular Clouds ◽  
Young Stars ◽  
Solar Neighborhood ◽  
Line Of Sight ◽  
Spiral Arms ◽  
Corotation Radius ◽  
Theoretical Conception

The analysis of the observational line-of-sight radial velocity field of molecular clouds, connecting with young stars, has strengthened the Fridman's hypothesis (1994) on the possible existence of anticyclone in the solar neighborhood. Anticyclones are located near corotation radius of the observed spiral arms, a number of which is equal to a number of vortices. Our calculations show that the four-vortices model fits observational data fairly well.We shall not use any theoretical conception on the nature of spiral arms generation (bar, selfgravitational or hydrodynamical mechanisms, etc.). We shall base on the treatment of the observational data.

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 Molecular Clouds in Orion and Monoceros

1980 ◽  
Vol 87 ◽  
pp. 197-203 ◽  
Author(s):  
Mark Morris ◽  
J. Montani ◽  
P. Thaddeus
Keyword(s):  
Magnetic Fields ◽  
Radial Velocity ◽  
Millimeter Wave ◽  
Molecular Clouds ◽  
Gas Flow ◽  
Galactic Plane ◽  
Line Of Sight ◽  
Molecular Material ◽  
Velocity Gradients ◽  
Angular Extent

A 1.2-meter millimeter-wave telescope has been used to survey CO in the constellations of Orion and Monoceros. Many new molecular clouds have been found. The distribution of molecular material shows two striking characteristics: 1) Most of the molecular clouds in this region appear to be connected by continuous extensions and filaments. To judge from continuity in radial velocity, most of these connections appear to be real, and are not merely the result of projection along the line of sight. 2) There are at least two slender filamentary features longer than 10° in angular extent. These filaments may connect the molecular clouds lying well out of the Galactic plane to clouds lying in the plane. Their shape and orientation suggest that magnetic fields may play a role in their evolution. The observed velocity gradients may be explained by accelerated gas flow along the filament.

scholarly journals Density distribution and the radial velocity field in the spiral arms of M31

1970 ◽  
Vol 38 ◽  
pp. 42-50
Author(s):  
J. Einasto ◽  
U. Rümmel
Keyword(s):  
Integral Equation ◽  
Velocity Field ◽  
Density Distribution ◽  
Radial Velocity ◽  
Rotational Velocity ◽  
Resolving Power ◽  
Optical Data ◽  
Linear Integral Equation ◽  
Two Dimensional ◽  
Spiral Arms

The density distribution and the radial velocity field in the Andromeda galaxy, M 31, have been studied on the basis of the 21-cm radio-line data from Jodrell Bank and Green Bank. The true density has been obtained from the observed one by solving a two-dimensional integral equation. As the resolving power of the radio telescopes is too low to locate all spiral arms separately, optical data on the distribution of ionized hydrogen clouds have been also used. The mean radial velocities have been derived by solving a two-dimensional non-linear integral equation with the help of hydrogen densities, and a model radial velocity field.The inner concentrations of hydrogen form two patchy ringlike structures with mean radii 30′ and 50′, the outer concentrations can be represented as fragments of two leading spiral arms.The rotational velocity, derived from the radial velocity field, in the central region differs considerably from the velocity curves obtained by earlier authors. The difference can be explained by the fact that in this region the correction for the antenna beam width is much greater than adopted by previous investigators.

scholarly journals Triggering the Formation of Young Clusters

2002 ◽  
Vol 207 ◽  
pp. 390-400
Author(s):  
Bruce G. Elmegreen
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Young Stars ◽  
Solar Neighborhood ◽  
Number Of Clusters ◽  
Spiral Arms ◽  
Star Forming ◽  
Gravitational Instabilities ◽  
Galaxy Disk

Star formation is triggered in essentially three ways: (1) the pressures from existing stars collect and squeeze nearby dense gas into gravitationally unstable configurations, (2) random compression from supersonic turbulence makes new clouds and clumps, some of which are gravitationally unstable, and (3) gravitational instabilities in large parts of a galaxy disk make giant new clouds and spiral arms that fragment by the other two processes into a hierarchy of smaller star-forming pieces. Examples of each process are given. Most dense clusters in the solar neighborhood were triggered by external stellar pressures. Most clusters and young stars on larger scales are organized into hierarchical patterns with an age-size correlation, suggestive of turbulence. Beads-on-a-string of star formation in spiral arms and resonance rings indicate gravitational instabilities. The turbulence model explains the mass spectrum of clusters, the correlation between the fraction of star formation in the form of clusters and the star formation rate, found by Larsen & Richtler, and the correlation between the size of the largest cluster and the number of clusters in a galaxy.

scholarly journals The Ballistic Particle Model

1983 ◽  
Vol 100 ◽  
pp. 133-134
Author(s):  
Frank N. Bash
Keyword(s):  
Radial Velocity ◽  
Gravitational Potential ◽  
Molecular Clouds ◽  
Milky Way ◽  
Terminal Velocity ◽  
Particle Model ◽  
The Sun ◽  
Giant Molecular Clouds ◽  
Spiral Pattern ◽  
Armed Spiral

Bash and Peters (1976) suggested that giant molecular clouds (GMC's) can be viewed as ballistic particles launched from the two-armed spiral-shock (TASS) wave with orbits influenced only by the overall galactic gravitational potential perturbed by the spiral gravitational potential in the arms. For GMC's in the Milky Way, the model predicts that the radial velocity observed from the Sun increases with age (time since launch). We showed that the terminal velocity of CO observed from l ≃ 30° to l ≃ 60° can be understood if all GMC's are born in the spiral pattern given by Yuan (1969) and live 30 × 106 yrs. Older GMC's were predicted to have radial velocities which exceed observed terminal velocities.

scholarly journals An overview of the structure and kinematics of the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 15-23 ◽  
Author(s):  
B. E. Westerlund
Keyword(s):  
Star Formation ◽  
Observational Data ◽  
Spiral Structure ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Line Of Sight ◽  
Small Magellanic Cloud ◽  
Complex Velocity ◽  
The Past

A vast amount of observational data concerning the structure and kinematics of the Magellanic Clouds is now available. Many basic quantities (e.g. distances and geometry) are, however, not yet sufficiently well determined. Interactions between the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC) and our Galaxy have dominated the evolution of the Clouds, causing bursts of star formation which, together with stochastic self-propagating star formation, produced the observed structures. In the youngest generation in the LMC it is seen as an intricate pattern imitating a fragmented spiral structure. In the SMC much of the fragmentation is along the line of sight complicating the reconstruction of its history. The violent events in the past are also recognizable in complex velocity patterns which make the analysis of the kinematics of the Clouds difficult.

scholarly journals Hypersonic swizzle sticks: jets, fossil cavities and turbulence in molecular clouds

2006 ◽  
Vol 2 (S237) ◽  
pp. 172-176
Author(s):  
Andrew J Cunningham ◽  
Adam Frank ◽  
Eric G Blackman ◽  
Alice Quillen
Keyword(s):  
Turbulent Flows ◽  
Molecular Clouds ◽  
Turbulent Medium ◽  
Young Stars ◽  
Turbulence Energy ◽  
Theoretical Simulation ◽  
Bow Shocks ◽  
Ambient Gas ◽  
Energy And Momentum ◽  
Ability To Drive

AbstractThe ubiquity and high density of outflows from young stars in clusters make them an intriguing candidate for the source of turbulence energy in molecular clouds. In this contribution we discuss new studies, both observational and theoretical, which address the issue of jet/outflow interactions and their ability to drive turbulent flows in molecular clouds. Our results are surprising in that they show that fossil cavities, rather than bow shocks from active outflows, constitute the mechanism of re-energizing turbulence. We first present simulations which show that collisions between active jets are ineffective at converting directed momentum and energy in outflows into turbulence. This effect comes from the ability of radiative cooling to constrain the surface area through which colliding outflows entrain ambient gas. We next discuss observational results which demonstrate that fossil cavities from “extinct” outflows are abundant in molecular material surrounding clusters such as NGC 1333. These structures, rather than the bow shocks of active outflows, comprise the missing link between outflow energy input and re-energizing turbulence. In a separate theoretical/simulation study we confirm that the evolution of cavities from decaying outflow sources leads to structures which match the observations of fossil cavities. Finally we present new results of outflow propagation in a fully turbulent medium exploring the explicit mechanisms for the transfer of energy and momentum between the driving wind and the turbulent environment.

Far-ultraviolet Variables in M31: Concentration in Spiral Arms and Association with Young Stars

2021 ◽  
Vol 162 (5) ◽  
pp. 199
Author(s):  
Denis A. Leahy ◽  
Megan Buick ◽  
Joseph E. Postma
Keyword(s):  
Young Stars ◽  
Spiral Arms ◽  
Far Ultraviolet
Sign in / Sign up

Export Citation Format

Share Document