scholarly journals New light on the corrugation phenomenon in our Galaxy

1985 ◽  
Vol 106 ◽  
pp. 175-178
Author(s):  
J. V. Feitzinger ◽  
J. Spicker
Keyword(s):  
Velocity Field ◽  
Radial Velocity ◽  
Density Wave ◽  
Radial Expansion ◽  
Spiral Pattern ◽  
Mass Model ◽  
Wave Kinematics ◽  
Spiral Arm

This investigation presents a total picture of the well-known corrugation-phenomenon for the (heliocentric) longitude range 10° ≤ 1 ≤ 240° as derived from HI-studies. For each spiral arm of the spiral pattern of Simonson (1976), we derived the centroid of the HI distribution from the 21-cm line surveys of Weaver and Williams (1974), Sinha (1979), and Westerhout and Wendlandt (1982). The three-component mass model of Rohlfs and Kreitschmann (1981) was used to derive a radial-velocity field, which was supplemented by a radial expansion field and by density-wave kinematics. This combined field served to calculated kinematic distances. The warp was taken into account according to Henderson et al. (1982) and Kulkarni et al. (1982).

scholarly journals Possible Pattern Speeds of a Density Wave in our Galaxy

1977 ◽  
Vol 45 ◽  
pp. 279-282 ◽  
Author(s):  
Preben J. Grosbøl
Keyword(s):  
Velocity Field ◽  
Spiral Structure ◽  
Density Wave ◽  
Wave Theory ◽  
Young Stars ◽  
Spiral Pattern ◽  
Considerable Effort ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Density Wave Theory

Since the density wave theory was introduced by Lin and Shu (1964) to explain the spiral structure considerable effort has been made to detect this kind of wave in our galaxy and to determine its parameters. Observations of the distribution and velocity field of gas and young objects show the present shape and location of the spiral pattern in our galaxy but tell little about its angular velocity. It was proposed by Strömgren (1967) to estimate this important parameter by calculating the places of formation of moderately young stars for which accurate space velocities and ages are known. This was done assuming that the majority of stars is formed in spiral arms so that the stellar birthplaces would outline the position of the spiral pattern at different epochs. Later, Yuan (1969) and Wielen (1973) calculated stellar birthplaces in the spiral potential given by Lin et al. (1969). These investigations showed no disagreement with the assumed density wave, however, the number of stars was too small to verify the assumed pattern speed.

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 7.15. The Fourier analysis of the observed velocity field of gas in the inner 1.5 pc of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 321-324
Author(s):  
A.M. Fridman ◽  
V.V. Lyakhovich ◽  
O.V. Khoruzhii ◽  
O.K. Silchenko
Keyword(s):  
Velocity Field ◽  
Fourier Analysis ◽  
Galactic Center ◽  
Second Harmonic ◽  
Density Wave ◽  
Ionized Gas ◽  
Density Maximum ◽  
Fourier Harmonic ◽  
Wave Nature ◽  
The Galaxy

The Fourier analysis of the observed velocity field of ionized gas in the inner 1.5 pc of the Galactic Center (obtained by Roberts and Goss, 1993) is made. As follows from the analysis, the observed field of residual velocities is dominated by the second Fourier harmonic. This fact can be treated as a consequence of the presence of an one-armed density wave with the density maximum along the Northern Arm plus the Western Arc structure. The wave nature of this structure is proved on the base of the behaviour of the phase of the second harmonic of line-of-sight velocity field in the whole region. The Fourier analysis shows also the presence of systematic radial velocity. We consider this flow as a quasi-stationary radial drift caused by one-armed nonlinear density wave (‘mini-spiral’).

scholarly journals Gas Response to a Rotating Stellar Bar

1978 ◽  
Vol 3 (3) ◽  
pp. 234-236
Author(s):  
M. P. Schwarz
Keyword(s):  
Spiral Galaxies ◽  
Fast Rate ◽  
Density Wave ◽  
Wave Theory ◽  
Finite Amplitude ◽  
Spiral Waves ◽  
Galactic Rotation ◽  
Spiral Pattern ◽  
Density Wave Theory ◽  
Gas Response

The arms in spiral galaxies cannot be material arms for then they would wind up on a time scale of one galactic rotation, or a few times 108 years. The large number of spirals suggests that the spiral pattern must persist for about 1010 years (or be continually rejuvenated). The density wave theory treats the spiral pattern as a wave phenomenon, thus overcoming this problem. Much work has been done studying small amplitude oscillations in flat stellar discs. Self-consistent spiral modes have been found, but they are not stable and grow at a fast rate. Numerical simulations of thin stellar discs, such as those of Hohl (1971), which can handle finite amplitude waves, have been more successful. Spiral waves form initially but evolve into a steady state rotating bar. It seems therefore, that a long-lived spiral cannot be formed in stars alone.

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 Signatures of long-lived spiral patterns: The color gradient trend

2012 ◽  
Vol 10 (H16) ◽  
pp. 323-323
Author(s):  
Eric E. Martínez-García ◽  
Rosa Amelia González-Lópezlira
Keyword(s):  
Stellar Population ◽  
Density Wave ◽  
Wave Theory ◽  
Disk Galaxies ◽  
Population Synthesis ◽  
Spiral Pattern ◽  
Stellar Population Synthesis ◽  
Color Gradient ◽  
Pattern Speeds ◽  
Density Wave Theory

AbstractBased both on observations and simulations, recent works propose that the speed of the spiral pattern in disk galaxies may decrease with increasing radius; the implications are that patterns are actually short-lived, and that the azimuthal color/age gradients across spiral arms predicted by density wave theory could not be produced. We, however, have consistently found such gradients, and measured spiral pattern speeds by comparing the observations with stellar population synthesis models (González & Graham 1996; Martínez-García et al. 2009a, b; Martínez-García & González-Lópezlira 2011). Here, we summarize our previous results in non-barred and weakly barred spirals, together with six new, as yet unpublished, objects. On the other hand, we have indeed found a trend whereby pattern speeds at smaller radii are larger than expected from a model that assumes purely circular orbits (cf. Figure 1), likely due to the effect of spiral shocks on the orbits of newborn stars. The results suggest that spirals may behave as steady long-lived patterns.

scholarly journals NGC 7479 — the Rosetta stone of minor mergers?

2000 ◽  
Vol 174 ◽  
pp. 334-334
Author(s):  
S. Laine
Keyword(s):  
Velocity Field ◽  
Total Mass ◽  
Velocity Fields ◽  
Nuclear Region ◽  
Neutral Gas ◽  
Rosetta Stone ◽  
Barred Spiral Galaxy ◽  
Minor Mergers ◽  
A Minor ◽  
Spiral Arm

The overall morphology of the barred spiral galaxy NGC 7479 was modelled numerically in a simple minor merger scenario. I paid special attention to the morphology and features of the velocity field along the dominant spiral arm. The mass of the merging companion was 1/30 of the total mass of the primary. The companion was started in a circular prograde orbit at six disk scale lengths from the centre of the primary. I followed the evolution of the merger until the companion had reached the nuclear region of the primary. A comparison between the modelled and observed morphologies of the stellar and the ionized and neutral gas distributions and velocity fields suggests that the transient look of NGC 7479 is a result of a minor merger. I also tested the effects of variations in several initial parameters of the merger. See Laine and Heller, 1999, for further details.

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