scholarly journals Manifold spirals in barred galaxies with multiple pattern speeds

2020 ◽  
Vol 636 ◽  
pp. A44
Author(s):  
C. Efthymiopoulos ◽  
M. Harsoula ◽  
G. Contopoulos
Keyword(s):  
Invariant Manifolds ◽  
Relative Phase ◽  
Spiral Structure ◽  
Galactic Disk ◽  
Time Varying ◽  
Barred Galaxies ◽  
Single Pattern ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Manifold Theory

In the manifold theory of spiral structure in barred galaxies, the usual assumption is that the spirals rotate with the same pattern speed as the bar. Here, we generalize the manifold theory under the assumption that the spirals rotate with a different pattern speed than the bar. More generally, we consider the case in which one or more modes, represented by the potentials V2, V3, etc., coexist in the galactic disk in addition to the bar’s mode Vbar, but the modes rotate with pattern speeds, Ω2, Ω3, etc., which are incommensurable between themselves and with Ωbar. Through a perturbative treatment (assuming that V2, V3, etc. are small with respect to Vbar), we then show that the unstable Lagrangian points L1 and L2 of the pure bar model (Vbar, Ωbar) are continued in the full model as periodic orbits, in the case of one extra pattern speed, or as epicyclic “Lissajous-like” unstable orbits, in the case of more than one extra pattern speeds. We use GL1 and GL2 to denote the continued orbits around the points L1 and L2. Furthermore, we show that the orbits GL1 and GL2 are simply unstable. As a result, these orbits admit invariant manifolds, which can be regarded as the generalization of the manifolds of the L1 and L2 points in the single pattern speed case. As an example, we computed the generalized orbits GL1, GL2, and their manifolds in a Milky-Way-like model in which bar and spiral pattern speeds were assumed to be different. We find that the manifolds produce a time-varying morphology consisting of segments of spirals or “pseudorings”. These structures are repeated after a period equal to half the relative period of the imposed spirals with respect to the bar. Along one period, the manifold-induced time-varying structures are found to continuously support at least some part of the imposed spirals, except at short intervals around specific times at which the relative phase of the imposed spirals with respect to the bar is equal to ±π/2. The connection of these effects to the phenomenon of recurrent spirals is discussed.

scholarly journals Bar pattern speeds in CALIFA galaxies

2019 ◽  
Vol 632 ◽  
pp. A51 ◽  
Author(s):  
Virginia Cuomo ◽  
J. Alfonso Lopez Aguerri ◽  
Enrico Maria Corsini ◽  
Victor P. Debattista ◽  
Jairo Méndez-Abreu ◽  
...  
Keyword(s):  
Formation Process ◽  
Systematic Investigation ◽  
Sloan Digital Sky Survey ◽  
Stellar Kinematics ◽  
Barred Galaxies ◽  
Tidal Interaction ◽  
Wide Range ◽  
Area Survey ◽  
Pattern Speed ◽  
Pattern Speeds

Context. About 35% of the nearby disc galaxies host a weak bar for which different formation scenarios, including the weakening of a strong bar and tidal interaction with a companion, have been suggested. Measuring the bar pattern speeds of a sample of weakly barred galaxies is a key step in constraining their formation process, but such a systematic investigation is still missing. Aims. We investigated the formation process of weak bars by measuring their properties in a sample of 29 nearby weakly barred galaxies, spanning a wide range of morphological types and luminosities. The sample galaxies were selected to have an intermediate inclination, a bar at an intermediate angle between the disc minor and major axes, and an undisturbed morphology and kinematics to allow the direct measurement of the bar pattern speed. Combining our analysis with previous studies, we compared the properties of weak and strong bars. Methods. We measured the bar radius and strength from the r band images available in the Sloan Digital Sky Survey and bar pattern speed and corotation radius from the stellar kinematics obtained by the Calar Alto Legacy Integral Field Area Survey. We derived the bar rotation rate as the ratio between the corotation and bar radii. Results. Thirteen out of 29 galaxies (45%), which were morphologically classified as weakly barred from a visual inspection, do not actually host a bar component or their central elongated component is not in rigid rotation. We successfully derived the bar pattern speed in 16 objects. Two of them host an ultrafast bar. Using the bar strength to differentiate between weak and strong bars, we found that the weakly barred galaxies host shorter bars with smaller corotation radii than their strongly barred counterparts. Weak and strong bars have similar bar pattern speeds and rotation rates, which are all consistent with being fast. We did not observe any difference between the bulge prominence in weakly and strongly barred galaxies, whereas nearly all the weak bars reside in the disc inner parts, contrary to strong bars. Conclusions. We ruled out that the bar weakening is only related to the bulge prominence and that the formation of weak bars is triggered by the tidal interaction with a companion. Our observational results suggest that weak bars may be evolved systems exchanging less angular momentum with other galactic components than strong bars.

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 Relations among structural parameters in barred galaxies with a direct measurement of bar pattern speed

2020 ◽  
Vol 641 ◽  
pp. A111
Author(s):  
V. Cuomo ◽  
J. A. L. Aguerri ◽  
E. M. Corsini ◽  
V. P. Debattista
Keyword(s):  
Direct Measurement ◽  
Structural Parameters ◽  
Host Galaxies ◽  
Massive Galaxies ◽  
Barred Galaxies ◽  
Stellar Spectroscopy ◽  
Corotation Radius ◽  
Wide Range ◽  
Pattern Speed ◽  
Pattern Speeds

We investigate the relations between the properties of bars and their host galaxies in a sample of 77 nearby barred galaxies, spanning a wide range of morphological types and luminosities, with 34 SB0-SBa and 43 SBab-SBc galaxies. The sample includes all the galaxies with reliable direct measurement of their bar pattern speed based on long-slit or integral-field stellar spectroscopy using the Tremaine-Weinberg method. We limited our analysis to the galaxies with a relatively small relative error on the bar pattern speed (≤50%) and that do not host an ultrafast bar. For each galaxy, we collected the radius, strength, pattern speed, corotation radius, and rotation rate for the bar and we also collected the Hubble type and absolute SDSS r-band magnitude. We also used literature bulge-to-total luminosity ratios for a subsample of 53 galaxies with an available photometric decomposition. We confirmed earlier observational findings that longer bars rotate at lower bar pattern speeds, shorter bars are weaker, and bars with a low rate of bar rotation rotate at faster bar pattern speeds and have smaller corotation radii. In addition, we found that stronger bars rotate at lower bar pattern speeds, as predicted from the interchange of angular momentum during bar evolution, which in turn may depend on different galaxy properties. Moreover, we report that brighter galaxies host longer bars, which rotate at lower bar pattern speeds and have larger corotation radii. This result is in agreement with a scenario of downsizing in bar formation, if more massive galaxies formed earlier and had sufficient time to slow down, grow in length, and push corotation outwards.

scholarly journals Multiple bars and secular evolution

2012 ◽  
Vol 10 (H16) ◽  
pp. 327-327
Author(s):  
Juntai Shen
Keyword(s):  
Near Infrared ◽  
Initial Conditions ◽  
Galactic Nuclei ◽  
Building Blocks ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Stellar Velocity ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Short Time

AbstractBars are the most important driver of secular evolution. A significant fraction of barred galaxies also harbor small secondary bars. Secondary bars are visible even in near-infrared images, so they are not just dusty and blue, but stellar features (Erwin & Sparke 2002). Since they are quite common, secondary bars are probably long-lived stellar features. The random relative orientation of the two bars indicates that they are dynamically decoupled with different pattern speeds (Buta & Crocker 1993). Corsini et al. (2003) presented conclusive direct kinematic evidence for a decoupled secondary bar in NGC 2950. Dynamically decoupled secondary bars have long been hypothesized to be a mechanism to drive gas past the ILR of primary bars to feed active galactic nuclei (Shlosman et al. 1989). However, the dynamics of secondary bars are still not well understood, and it is still unclear what role secondary bars play in the AGN fueling process.Numerical simulations offer the best approach to understanding double-barred systems. Decoupled secondary bar in the earlier gaseous simulations only last a short time (< 1 Gyr, e.g. Friedli & Martinet 1993). Orbital studies of double-barred systems discovered a family of loop orbits that may be building blocks of long-lived nuclear stellar bars (Maciejewski & Sparke 1997, 2000). To complement orbital studies, which are not fully self-consistent, N-body simulations are preferred to further our understanding of double-barred systems. Debattista & Shen (2007) and Shen & Debattista (2009) managed to form long-lived double-barred systems with purely collisionless simulations, where a pre-existing rotating pseudo-bulge is introduced initially. The shape and size of secondary bars in the models are comparable to observed ones. They found that the rotation of the two bars is not rigid. The amplitude and pattern speed of the secondary bars oscillate as they rotate through their primary counterparts. Although the secondary bar rotates faster than the primary bar in this model, the stellar velocity field in the central region only shows a weakly twisted kinematic minor axis.Recently more simulations of double-barred galaxies with simpler initial conditions are explored (Du, Shen & Debattista 2014). We expect that the new models can be used to cross-check with the kinematic properties of double-barred galaxies from IFU observations such as SAURON and Atlas3D.

scholarly journals Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

2020 ◽  
Author(s):  
Bogdan C Ciambur ◽  
Francesca Fragkoudi ◽  
Sergey Khoperskov ◽  
Paola Di Matteo ◽  
Françoise Combes
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Large Fraction ◽  
Formation Time ◽  
Dark Matter Halo ◽  
Barred Galaxies ◽  
Pattern Speed ◽  
Nearby Galaxies ◽  
Dynamical Instabilities ◽  
Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

Dynamical imprint of interstellar gas on persistence of spiral structure in galaxies

2017 ◽  
Vol 13 (S334) ◽  
pp. 296-297
Author(s):  
Soumavo Ghosh ◽  
Chanda J. Jog
Keyword(s):  
Time Scale ◽  
Spiral Structure ◽  
Density Wave ◽  
Disk Galaxies ◽  
Interstellar Gas ◽  
Spiral Arms ◽  
Pattern Speed

AbstractThe persistence of the spiral structure in disk galaxies has long been debated. In this work, we investigate the dynamical influence of interstellar gas on the persistence of the spiral arms in disk galaxies. We show that the gas helps the spiral arms to survive for longer time-scale (~ a few Gyr). Also, we show that the addition of gas in calculation is necessary for getting a stable density wave corresponding to the observed pattern speed of the spiral arms.

scholarly journals Computer models of spiral structure

1970 ◽  
Vol 38 ◽  
pp. 368-372 ◽  
Author(s):  
F. Hohl
Keyword(s):  
Motion Picture ◽  
Computer Model ◽  
Spiral Structure ◽  
Galactic Disk ◽  
Equations Of Motion ◽  
Computer Models ◽  
The Self ◽  
Large Numbers ◽  
Self Consistent

A computer model for isolated disks of stars is used to study the self-consistent motion of large numbers of point masses as they move in the plane of the galactic disk. The Langley Research Center's CDC 6600 computers are used to integrate the equations of motion for systems containing from 50000 to 200000 stars. The results are presented in the form of a motion picture.

scholarly journals On a mechanism that structures galaxies

1979 ◽  
Vol 84 ◽  
pp. 157-158
Author(s):  
D. Lynden-Bell
Keyword(s):  
Angular Momentum ◽  
Differential Rotation ◽  
Spiral Structure ◽  
Rotation Curves ◽  
Eccentric Orbits ◽  
The Galaxy ◽  
Central Regions ◽  
Pattern Speed ◽  
Stellar Orbit ◽  
Lindblad Resonance

By considering the interaction of a single stellar orbit with a weak cos 2Φ potential it is shown that in the central regions of galaxies with slowly rising rotation curves, the elongations of the orbits will align along any potential valley and oscillate about it. This effect is more pronounced for elongated orbits. In such regions any pair of orbits will naturally align under their mutual gravity and so a bar will form. The gravity of this bar will drive a spiral structure in the outer parts of the galaxy where differential rotation is too strong to allow the orbits to be caught by the bar. The spiral structure carries a torque which slowly drains angular momentum from the bar, gradually making its outline more eccentric and slowing its pattern speed. In the outer parts of the bar only the more eccentric orbits align with the potential valley; the rounder ones form a ring or lens about the bar. As the pattern speed slows down, the corotation resonance and outer Lindblad resonance, which receive the angular momentun, move outwards. The evolution of the system is eventually slowed down by the weakness of these outer resonances where the material is rather sparse.

scholarly journals Modelling the Structure of the Ringed Spiral NGC 4736

1996 ◽  
Vol 157 ◽  
pp. 253-255
Author(s):  
Wim van Driel ◽  
Pieter Mulder ◽  
Françoise Combes
Keyword(s):  
Mass Distribution ◽  
Spiral Structure ◽  
Optical Spectra ◽  
Spectral Lines ◽  
Time Interval ◽  
Limited Time ◽  
The Galaxy ◽  
Dynamical Simulations ◽  
Pattern Speed ◽  
Limited Time Interval

AbstractWe studied the ringed RSab(r)-type spiral NGC 4736, which has a probably slightly oval disk and a very small bar. We mapped the galaxy in the HI and Hα spectral lines and we obtained long-slit optical spectra. These data were modeled using a 2-D gas dynamical code. The 2-D potential used is axisymmetric in the inner and outer regions and oval (b/a=0.8) at intermediate radii only. The oval component rotates at a pattern speed of 40 km s–1 kpc–1, close to the observed value. Inner and outer rings, like those observed, form at the inner and outer Lindblad resonances, though they co-exist only during a limited time interval in the simulations. The morphology and kinematics of the inner ring and spiral structure as observed in neutral and ionized hydrogen can be well understood in terms of gas dynamical simulations, given the form of the (stellar) potential. What remains to be explained is the origin of the nonaxisymmetric features in the mass distribution defining the potential.

Sign in / Sign up

Export Citation Format

Share Document