scholarly journals The shapes of spiral arms in the S4G survey and their connection with stellar bars

2019 ◽  
Vol 631 ◽  
pp. A94 ◽  
Author(s):  
S. Díaz-García ◽  
H. Salo ◽  
J. H. Knapen ◽  
M. Herrera-Endoqui

Context. Spiral galaxies are very common in the local Universe, but their formation, evolution, and interplay with bars remain poorly understood after more than a century of astronomical research on the topic. Aims. We use a sample of 391 nearby galaxies from the S4G survey to characterise the winding angle and amplitude of spiral arms as a function of disc properties, such as bar strength, in all kinds of spirals (grand-design, multi-armed, and flocculent). Methods. We derived global pitch angles in 3.6 μm de-projected images from (i) average measurements of individual logarithmic spiral segments, and (ii) for a subsample of 32 galaxies, from 2D Fourier analyses. The strength of spirals was quantified from the tangential-to-radial force ratio and from the normalised m = 2 Fourier density amplitudes. Results. In galaxies with more than one measured logarithmic segment, the spiral pitch angle varies on average by ∼10° between segments, but by up to ≳15 − 20°. The distribution of the global pitch angle versus Hubble type (T) is very similar for barred and non-barred galaxies when 1 ≲ T ≲ 5. Most spiral galaxies (> 90%) are barred for T >  5. The pitch angle is not correlated with bar strength, and only weakly with spiral strength. The amplitude of spirals is correlated with bar strength (and less tightly, with bar length) for all types of spirals. The mean pitch angle is hardly correlated with the mass of the supermassive black hole (estimated from central stellar velocity dispersion), with central stellar mass concentration, or with shear, questioning previous results in the literature using smaller samples. Conclusions. We do not find observational evidence that spiral arms are driven by stellar bars or by invariant manifolds. Most likely, discs that are prone to the development of strong bars are also reactive to the formation of prominent spirals, explaining the observed coupling between bar and spiral amplitudes.

2004 ◽  
Vol 220 ◽  
pp. 277-278
Author(s):  
Glen Petitpas ◽  
Mousumi Das ◽  
Peter Teuben ◽  
Stuart Vogel

Two-dimensional velocity fields have been used to determine the dark matter properties of a sample of barred galaxies taken from the BIMA Survey of Nearby Galaxies (SONG). Preliminary results indicate that the maximal disk model is not appropriate in several galaxies in our sample, but higher resolution results will be needed to confirm this.


Author(s):  
Charles Francis ◽  
Erik Anderson

We describe the structure and composition of six major stellar streams in a population of 20 574 local stars in the New Hipparcos Reduction with known radial velocities. We find that, once fast moving stars are excluded, almost all stars belong to one of these streams. The results of our investigation have led us to re-examine the hydrogen maps of the Milky Way, from which we identify the possibility of a symmetric two-armed spiral with half the conventionally accepted pitch angle. We describe a model of spiral arm motions that matches the observed velocities and compositions of the six major streams, as well as the observed velocities of the Hyades and Praesepe clusters at the extreme of the Hyades stream. We model stellar orbits as perturbed ellipses aligned at a focus in coordinates rotating at the rate of precession of apocentre. Stars join a spiral arm just before apocentre, follow the arm for more than half an orbit, and leave the arm soon after pericentre. Spiral pattern speed equals the mean rate of precession of apocentre. Spiral arms are shown to be stable configurations of stellar orbits, up to the formation of a bar and/or ring. Pitch angle is directly related to the distribution of orbital eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve to form bars and rings. We show that orbits of gas clouds are stable only in bisymmetric spirals. We conclude that spiral galaxies evolve toward grand design two-armed spirals. We infer from the velocity distributions that the Milky Way evolved into this form about 9 billion years ago (Ga).


2016 ◽  
Vol 11 (S321) ◽  
pp. 123-123
Author(s):  
P.A. Patsis

AbstractIn several grand design barred-spiral galaxies it is observed a second, fainter, outer set of spiral arms. Typical examples of objects of this morphology can be considered NGC 1566 and NGC 5248. I suggest that such an overall structure can be the result of two dynamical mechanisms acting in the disc. The bar and both spiral systems rotate with the same pattern speed. The inner spiral is reinforced by regular orbits trapped around the stable, elliptical, periodic orbits of the central family, while the outer system of spiral arms is supported by chaotic orbits. Chaotic orbits are also responsible for a rhomboidal area surrounding the inner barred-spiral region. In general there is a discontinuity between the two spiral structures at the corotation region.


Author(s):  
C. Efthymiopoulos ◽  
P. Tsoutsis ◽  
C. Kalapotharakos ◽  
G. Contopoulos

2008 ◽  
Vol 495 (3) ◽  
pp. 743-758 ◽  
Author(s):  
P. Tsoutsis ◽  
C. Kalapotharakos ◽  
C. Efthymiopoulos ◽  
G. Contopoulos

1996 ◽  
Vol 157 ◽  
pp. 23-29
Author(s):  
Debra Meloy Elmegreen

AbstractPrevious optical surface photometry of barred spiral galaxies revealed that there are two distinct types of bars: large bars tend to have a nearly constant surface brightness (”flat“ bar), while smaller bars tend to have a decreasing surface brightness with a scale length similar to the disk (”exponential“ bar). Statistically, flat bars tend to occur in early Hubble types and exponential bars in later types. Studies of resonances in spirals indicate that flat bars end inside corotation, while exponential bars end between the inner Lindblad and 4:1 resonances. Near-infrared (JHK) surface photometry of bars is presented in order to compare the stellar distributions and bar potentials in flat and exponential barred galaxies. The presence of isophotal twists in some galaxies provides additional information on resonances. The grand design and fiocculent optical structures in the two types of barred galaxies will be compared and contrasted with their near-infrared light distributions.


Author(s):  
M. Romero-Gómez ◽  
E. Athanassoula ◽  
J. J. Masdemont ◽  
C. García-Gómez

2020 ◽  
Vol 500 (2) ◽  
pp. 2380-2400
Author(s):  
A Zurita ◽  
E Florido ◽  
F Bresolin ◽  
I Pérez ◽  
E Pérez-Montero

ABSTRACT We present here the second part of a project that aims at solving the controversy regarding the issue of the bar effect on the radial distribution of metals in the gas-phase of spiral galaxies. In Paper I, we presented a compilation of more than 2800 H ii regions belonging to 51 nearby galaxies for which we derived chemical abundances and radial abundance profiles from a homogeneous methodology. In this paper, we analyse the derived gas-phase radial abundance profiles of 12+log (O/H) and log (N/O), for barred and unbarred galaxies separately, and find that the differences in slope between barred and unbarred galaxies depend on galaxy luminosity. This is due to a different dependence of the abundance gradients (in dex kpc−1) on luminosity for the two types of galaxies: in the galaxy sample under consideration the gradients appear to be considerably shallower for strongly barred galaxies in the whole luminosity range, while profile slopes for unbarred galaxies become steeper with decreasing luminosity. Therefore, we only detect differences in slope for the lower luminosity (lower mass) galaxies (MB ≳ −19.5 or M* ≲ 1010.4 M⊙). We discuss the results in terms of the disc evolution and radial mixing induced by bars and spiral arms. Our results reconcile previous discrepant findings that were biased by the luminosity (mass) distribution of the sample galaxies and possibly by the abundance diagnostics employed.


2019 ◽  
Vol 15 (S341) ◽  
pp. 266-267
Author(s):  
Fumi Egusa ◽  
Erin Mentuch Cooper ◽  
Jin Koda ◽  
Junichi Baba

AbstractNumerical simulations of disk galaxies with steady (long-lived) and dynamic (short-lived) spiral arms suggest that offsets between stellar and gas spiral arms depend on their nature or lifetime (Baba et al.2015). Based on this theoretical study, we investigated gas-star offsets in the nearby grand-design spiral galaxy M51, and found that its two spiral arms exhibit different offset dependences against radius. One arm is consistent with a steady arm, while the other is consistent with a dynamic arm. We deduce that this difference is likely due to a tidal interaction with the companion galaxy (Egusa et al.2017). For this study, a stellar mass distribution with a high accuracy at a high spatial resolution is essential, which has come to be available by applying recent SED fitting techniques to multi-wavelength images. We are now working to extend this study to other nearby spiral galaxies.


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