Spiral structure in barred galaxies. Observational constraints to spiral arm formation mechanisms

AbstractThe dynamical mechanism to form rings at Lindblad resonances in a barred galaxy is now well-known: due to its dissipative character, the gas is forced in a spiral structure, and experiences torques from the bar potential. Angular momentum is transferred until gas accumulates in the resonant rings. Some problems remain however to account for all observations, such as the very different time-scales for nuclear, inner and outer ring formation, while the three are frequently observed in the same galaxy; the shapes, orientations and thickness of the rings, etc... The adequacy of the present gas dynamical modelizations is discussed.Lenses are secondary components of barred galaxies that could originate from bar evolution. No model until now has met the observational constraints, in particular the sharp edge of the lenses, their strong velocity anisotropy, and their small thickness. We propose here that lenses are the result of partial bar destruction, a necessary step in a feedback cycle of bar formation-destruction, a cycle driven by gas accretion.

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3D MHD simulations of magnetic fields and radio polarization of barred galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031299 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 553-554

Author(s):

B. Kulesza-Żydzik ◽

K. Kulpa-Dybeł ◽

K. Otmianowska-Mazur ◽

G. Kowal ◽

M. Soida

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Spiral Structure ◽

Three Dimensional ◽

Barred Galaxies ◽

Mhd Simulations ◽

Large Scale Magnetic Field ◽

Strong Compression ◽

Dynamo Process ◽

Spiral Arm

AbstractWe present results of three-dimensional, fully nonlinear MHD simulations of a large-scale magnetic field evolution in a barred galaxy. The model does not take into consideration the dynamo process. We find that the obtained magnetic field configurations are highly similar to the observed maps of the polarized intensity of barred galaxies, because the modeled vectors form coherent structures along the bar and spiral arms. Due to the dynamical influence of the bar the gas forms spiral waves which go radially outward. Each spiral arm forms the magnetic arm which stays much longer in the disk, than the gaseous spiral structure. Additionally the modeled total energy of magnetic field grows due to strong compression and shear of non-axisymmetrical bar flows and differential rotation, respectively.

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Manifold spirals in barred galaxies with multiple pattern speeds

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936871 ◽

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.

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A Nuclear Ring in the Sa(r!) Galaxy NGC 7742

International Astronomical Union Colloquium ◽

10.1017/s0252921100049460 ◽

1996 ◽

Vol 157 ◽

pp. 83-85 ◽

Cited By ~ 1

Author(s):

K. Wakamatsu ◽

M. Hamabe ◽

M. T. Nishida ◽

A. Tomita

Keyword(s):

Elliptical Galaxy ◽

Formation Mechanisms ◽

Main Body ◽

Circular Symmetry ◽

Barred Galaxies ◽

Exclamation Mark ◽

The Galaxy ◽

Nuclear Ring ◽

Lindblad Resonance ◽

Inner Lindblad Resonance

NGC 7742 is well known for its prominent blue nuclear ring around an EO-like core, and so appears as a Hoag-type galaxy, an elliptical galaxy with an outer ring (Schweizer et al. 1987). The galaxy is classified as Sa(r!) in the Revised Shapley-Ames Catalog (Sandage and Tammann 1987) with an exclamation mark to emphasize the prominence of the ring. Its photographs are published in Laustsen et al. (1987), Wray (1988), and Sandage & Bedke (1994).The ring has a diameter of 19″ = 1.6 kpc at a distance of 17.1 Mpc (Buta & Crocker 1993), and so should be a nuclear ring of the galaxy. Nuclear rings and pseudorings are often detected in strongly barred (SB) galaxies, and interpreted to be linked to the inner Lindblad resonance (Buta & Crocker 1993). These nuclear features are, however, also found in some weakly-barred (SAB) and non-barred (SA) galaxies. NGC 7742 is a galaxy of the highest circular symmetry in its core, ring, and main body, and so the best object for a detailed study of formation mechanisms of nuclear rings in non-barred galaxies.

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Local stellar distribution and galactic spiral structure

Symposium - International Astronomical Union ◽

10.1017/s007418090000053x ◽

1970 ◽

Vol 38 ◽

pp. 189-198 ◽

Cited By ~ 1

Author(s):

S. W. McCuskey

Keyword(s):

Spiral Structure ◽

The Sun ◽

Long Period ◽

Classical Cepheids ◽

Galactic Clusters ◽

The Galaxy ◽

Galactic Spiral Structure ◽

Ob Associations ◽

Galactic Spiral ◽

Spiral Arm

Aside from the well-known spiral arm tracers such as the OB associations, young galactic clusters, WR stars and possibly the long-period classical cepheids, the more common stars in the neighborhood of the sun within 2 kpc show little or no relationship to the local spiral structure of the galaxy.

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Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey

Symposium - International Astronomical Union ◽

10.1017/s0074180900096297 ◽

1987 ◽

Vol 115 ◽

pp. 499-499 ◽

Cited By ~ 2

Author(s):

P. M. Solomon

Keyword(s):

Molecular Clouds ◽

Galactic Plane ◽

Far Infrared ◽

Formation Mechanisms ◽

H Ii Regions ◽

Giant Molecular Clouds ◽

Star Forming ◽

The Galaxy ◽

Two Populations ◽

Spiral Arm

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.

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Formation of Giant Molecular Clouds by Coagulation of Small Molecular Clouds in a Spiral Gravitational Potential

Symposium - International Astronomical Union ◽

10.1017/s0074180900096352 ◽

1987 ◽

Vol 115 ◽

pp. 541-543

Author(s):

Kohji Tomisaka

Keyword(s):

Star Formation ◽

Time Evolution ◽

Gravitational Potential ◽

Formation Process ◽

Molecular Clouds ◽

Spiral Structure ◽

Giant Molecular Clouds ◽

Short Lifetime ◽

Spiral Arm

The formation process of giant molecular clouds (GMCs) is investigated from the standpoint of the coagulation theory of molecular clouds. Small clouds collide with each other and grow to become massive ones. Ultimately they form GMCs with a finite lifetime. The occurrence of star formation in a GMC destroys it and consequently small clouds are formed again. We study the time evolution of the clouds which move through a spiral gravitational potential by an N-body simulation. Then the ensemble of clouds responds to the spiral potential and forms a spiral structure similar to that produced by hydrodynamical galactic shock. It is shown that GMCs are formed in the spiral arm region by collisions between clouds. The distribution of GMCs indicates their short lifetime, of the order of a few times 107 years.

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The intrinsic shape of bulges in the CALIFA survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731823 ◽

2018 ◽

Vol 609 ◽

pp. A132 ◽

Cited By ~ 11

Author(s):

L. Costantin ◽

J. Méndez-Abreu ◽

E. M. Corsini ◽

M. C. Eliche-Moral ◽

T. Tapia ◽

...

Keyword(s):

Formation Mechanisms ◽

Massive Galaxies ◽

Barred Galaxies ◽

Total Luminosity ◽

Prolate Spheroids ◽

Intrinsic Shape ◽

Binary Mergers ◽

Crucial Information ◽

Nearby Galaxies ◽

Heterogeneous Class

Context.The intrinsic shape of galactic bulges in nearby galaxies provides crucial information to separate bulge types.Aims.We aim to derive accurate constraints to the intrinsic shape of bulges to provide new clues on their formation mechanisms and set new limitations for future simulations.Methods.We retrieved the intrinsic shape of a sample of CALIFA bulges using a statistical approach. Taking advantage of GalMer numerical simulations of binary mergers we estimated the reliability of the procedure. Analyzing thei-band mock images of resulting lenticular remnants, we studied the intrinsic shape of their bulges at different galaxy inclinations. Finally, we introduced a new (B/A,C/A) diagram to analyze possible correlations between the intrinsic shape and the properties of bulges.Results.We tested the method on simulated lenticular remnants, finding that for galaxies with inclinations of 25° ≤θ≤ 65° we can safely derive the intrinsic shape of their bulges. We found that our CALIFA bulges tend to be nearly oblate systems (66%), with a smaller fraction of prolate spheroids (19%), and triaxial ellipsoids (15%). The majority of triaxial bulges are in barred galaxies (75%). Moreover, we found that bulges with low Sérsic indices or in galaxies with low bulge-to-total luminosity ratios form a heterogeneous class of objects; additionally, bulges in late-type galaxies or in less massive galaxies have no preference for being oblate, prolate, or triaxial. On the contrary, bulges with high Sérsic index, in early-type galaxies, or in more massive galaxies are mostly oblate systems.Conclusions.We concluded that various evolutionary pathways may coexist in galaxies, with merging events and dissipative collapse being the main mechanisms driving the formation of the most massive oblate bulges and bar evolution reshaping the less massive triaxial bulges.

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