Pitch Angle of Galactic Spiral Arms

Michikoshi, Shugo; Kokubo, Eiichiro

doi:10.1088/0004-637x/787/2/174

Cited by 31 publications

(55 citation statements)

References 28 publications

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“…arm segments, which reconnect and make up the spiral arms. The simulations of Grand et al (2013) and Michikoshi & Kokubo (2014), marked by green crosses and blue triangles in Figure 12, share the same general tendency for ϕ to decline with increasing Γ. However, a systematic offset can be clearly seen.…”

Section: Shear Ratesupporting

confidence: 59%

“…This is because Eq. (4) assumes Q > 1.5, which is indeed the case for the simulated spiral galaxies of Michikoshi & Kokubo (2014). However, as suggested by Bertin et al (1989a), because of self-regulation of gas content, Toomre's Q parameter in the outer regions of galactic disks should be close to unity.…”

Section: Shear Ratesupporting

confidence: 58%

“…where A is the first Oort constant and t = 0 means that the arm extends radially outward across the disk (ϕ = 90 • ). In the simulations of Michikoshi & Kokubo (2014), Toomre's Q parameter increases rapidly and exceeds 1.5 for Γ 0.5. In the linear approximation of swing amplification theory, if Q > 1.5, the maximum amplification is reached at t max ⋍ 3.5/κ, where κ is the epicyclic frequency.…”

Section: Shear Ratementioning

confidence: 90%

“…The Pearson's correlation coefficient, ρ, is shown on the bottom-left corner. and the pitch angle of the simulated spirals (Grand et al 2013;Michikoshi & Kokubo 2014). Michikoshi & Kokubo (2014) derived a theoretical relation between ϕ and Γ in the context of swing amplification theory.…”

Section: Shear Ratementioning

confidence: 99%

See 3 more Smart Citations

On the Connection between Spiral Arm Pitch Angle and Galaxy Properties

2019

ApJ

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We measure the pitch angle (ϕ) of spiral arms in a sample of 79 galaxies to perform a systematic study of the dependence of ϕ on galaxy morphology, mass, and kinematics to investigate the physical origin of spiral arms. We find that ϕ decreases (arms are more tightly wound), albeit with significant scatter, in galaxies with earlier Hubble type, more prominent bulges, higher concentration, and larger total galaxy stellar mass (M gal * ). For a given concentration, galaxies with larger stellar masses tend to have tighter spiral arms, and vice versa. We also find that ϕ obeys a tight inverse correlation with central stellar velocity dispersion for σ c 100 km s −1 , whereas ϕ remains approximately constant for σ c 100 km s −1 . We demonstrate that the ϕ -σ c and ϕ -M gal * relations are projections of a more fundamental three-dimensional ϕ − σ c − M gal * relation, such that pitch angle is determined by σ c for massive galaxies but by M gal * for less massive galaxies. Contrary to previous studies, we find that ϕ correlates only loosely with the galaxy's shear rate. For a given shear rate, spirals generated from Nbody simulations exhibit much higher ϕ than observed, suggesting that galactic disks are dynamically cooler (Toomre's Q ≈ 1.2). Instead, the measured pitch angles show a much stronger relation with morphology of the rotation curve of the central region, such that galaxies with centrally peaked rotation curves have tight arms, while those with slow-rising rotation curves have looser arms. These behaviors are qualitatively consistent with predictions of density wave theory.

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Section: Shear Ratesupporting

confidence: 59%

Section: Shear Ratesupporting

confidence: 58%

Section: Shear Ratementioning

confidence: 90%

Section: Shear Ratementioning

confidence: 99%

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On the Connection between Spiral Arm Pitch Angle and Galaxy Properties

2019

ApJ

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“…However, the pitch angle of these short-lived arms is quite large, i = 20-30 • . The theoretical prediction of its value is i = 24 • (Melnik & Rautiainen 2013;Michikoshi & Kokubo 2014). But the Galactic global spiral arms seem to have a considerably smaller pitch angle, 10-15 • (for example, Georgelin & Georgelin 1976;Russeil 2003;Vallée 2015, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Galactic resonance rings: modelling of motions in the wide solar neighbourhood

Melnik

2019

Monthly Notices of the Royal Astronomical Society

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Models of the Galaxy with analytical Ferrers bars can reproduce the residual velocities of OB-associations in the Sagittarius, Perseus and Local System stellar-gas complexes located within 3 kpc solar neighborhood. Ferrers ellipsoids with density distribution defined by power indices n = 1 and 2 are considered. The success in the reproduction of the velocity in the Local System is due to the large velocity dispersion which weakens the resonance effects by producing smaller systematic motions. Model galaxies form nuclear, inner and outer resonance rings R 1 and R 2 . The outer rings R 2 manage to catch twice more particles than the rings R 1 . The outer Lindblad resonance of the bar (OLR) is located 0.4 kpc beyond the solar circle, R OLR = R 0 + 0.4 kpc, corresponding to the bar angular velocity of Ω b = 50 km s −1 kpc −1 . The solar position angle with respect to the bar, θ b , providing the agreement between model and observed velocities is 40-52 • . Unfortunately, models considered cannot reproduce the residual velocities in the Carina and Cygnus stellar-gas complexes. The redistribution of the specific angular momentum, L, is found near the Lindblad resonances of the bar (ILR and OLR): the average value of L increases (decreases) at the radii a bit smaller (larger) than those of the resonances that can be connected with the existence of two types of periodic orbits elongated perpendicular to each other there.

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Physical Properties of Tidal Features of Interacting Disk Galaxies: Three-Dimensional Self-Consistent Models

Lee

2015

ApJ

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Using self-consistent three-dimensional (3D) N -body simulations, we investigate the physical properties of non-axisymmetric features in a disk galaxy created by a tidal interaction with its companion. The primary galaxy consists of a stellar disk, a bugle, and a live halo, corresponding to Milky-Way type galaxies, while the companion is represented by a halo alone. We vary the companion mass and the pericenter distance to explore situations with differing tidal strength parameterized by either the relative tidal force P or the relative imparted momentum S. We find that the formation of a tidal tail in the outer parts requires P 0.05 or S 0.07. A stronger interaction results in a stronger, less wound tail that forms earlier. Similarly, a stronger tidal forcing produces stronger, more loosely wound spiral arms in the inner parts. The arms are approximately logarithmic in shape, with both amplitude and pitch angle decaying with time. The derived pattern speed decreases with radius and is close to the Ω − κ/2 curve at late time, with Ω and κ denoting the angular and epicycle frequencies, respectively. This suggests that the tidally-induced spiral arms are most likely kinematic density waves weakly modified by self-gravity. Compared to the razor-thin counterparts, arms in the 3D models are weaker, have a smaller pitch angle, and wind and decay more rapidly. The 3D density structure of the arms is well described by the concentrated and sinusoidal models when the arms are in the nonlinear and linear regimes, respectively. We demonstrate that dynamical friction between interacting galaxies transfers the orbital angular momentum of one galaxy to the spin angular momentum of the companion halo.

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Pitch Angle of Galactic Spiral Arms

Cited by 31 publications

References 28 publications

On the Connection between Spiral Arm Pitch Angle and Galaxy Properties

On the Connection between Spiral Arm Pitch Angle and Galaxy Properties

Galactic resonance rings: modelling of motions in the wide solar neighbourhood

Physical Properties of Tidal Features of Interacting Disk Galaxies: Three-Dimensional Self-Consistent Models

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