A dynamical instability of bars in disk galaxies

Raha, N.; Sellwood, J. A.; James, R. A.; Kahn, F. D.

doi:10.1038/352411a0

Cited by 472 publications

(511 citation statements)

References 12 publications

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“…At T=5 Gyr (shown in the figure), in both cases, this has resulted in a pronounced B/P/X edge-on morphology. The vertical evolution lacks therapid buckling phase often reported in the literature (Raha et al 1991), in which sense it is more reminiscentof the resonance heating models (Quillen et al 2014), where the X is associatedwith disk stars heated by the 2:1 vertical resonance (Combes et al 1990;Pfenniger & Friedli 1991;Patsis et al 2002). Most importantly for the current study, the face-on morphology for = B D 0.08 is similar to that in massive barred galaxies, with a dominant, round barlens structure and a weak, thin bar component (compare to NGC 4548 in the lowermost row; see for classification of observed barlens categories): this structure survived to the end of the simulation (12 Gyr).…”

Section: Simulationsmentioning

confidence: 99%

Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

Salo

Laurikainen

2017

ApJ

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We use stellar dynamical bulge/disk/halo simulations to study whether barlenses (lens-like structures embedded in the narrow bar component) are only the face-on counterparts of Boxy/Peanut/X-shapes (B/P/X) seen in edge-on bars, or if some additional physical parameter affects that morphology. A range of bulge-to-disk mass and size ratios are explored: our nominal parameters (, disk comprisingtwo-thirds of total force at h 2.2 r ) correspond to typical Milky Way mass galaxies. In all models, a bar with pronounced B/P/X forms in a few Gyr, visiblein the edge-on view. However, the pure barlens morphology forms only in models with sufficiently steep inner rotation curves,, achieved when including a small classical bulge with  B D 0.02 and  r h 0.1 r eff . For shallower slopes, the central structure still resembles a barlens, but shows a clear X signature even in low inclinations. A similar result holds for bulge-less simulations, where the central slope is modified by changing the halo concentration. The predicted sensitivity on the inner rotation curve is consistent with the slopes that are estimated from gravitational potentials calculated from the 3.6 μm images, for the observed barlens and X-shaped galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S 4 G). For inclinations <60°t he galaxies with barlenses have on average twice steeper inner rotation curves than galaxies with X shapes: the limiting slope is ∼250 km s −1 kpc −1 . Among barred galaxies, those with barlenses have both the strongest bars and the largest relative excess of inner surface density, both in barlens regions ( h 0.5 r ) and near the center ( h 0.1 r ); this provides evidence for bar-driven secular evolution in galaxies.

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Section: Simulationsmentioning

confidence: 99%

Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

Salo

Laurikainen

2017

ApJ

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“…The disk formed a bar thatsubsequently experienced vertical thickening via the buckling instability (Toomre 1966, p. 111;Raha et al 1991;Sellwood & Wilkinson 1993) and developed the peanut-shaped bulge that is characteristic of this instability. After the disk reached a nearly steady state (simulation time t 1 =700), a central point mass 5 representing an SMBH of mass 0.2% M d was grown adiabatically (for details see Brown et al 2013).…”

Section: Simulationsmentioning

confidence: 99%

“…Indeed, studies of orbits in 2D N-body bars largely confirmed the picture arising from the study of periodic orbits and showed that many regular orbits elongated along the bar were parented by x1 orbits, a small fraction were parented by retrograde x4 orbits (Sparke & Sellwood 1987), and none were parented by prograde x2 orbits. The realization that bars can also undergo buckling instabilities (Combes & Sanders 1981;Raha et al 1991), which makes them develop substantial vertical thickness and peanut-shaped morphologies, led to the study of periodic orbits in three-dimensional bars (Pfenniger 1984;Martinet & de Zeeuw 1988;Pfenniger & Friedli 1991;Skokos et al 2002aSkokos et al , 2002b. It was shown that theappearance of specific morphological features in images of bars, such as the X-shape and peanut features seen in edge-on bars and the boxy/rectangular isophotes and "ansae" of face-on bars, could be explained by orbits trapped around specific periodic orbit families (Patsis et al 2002(Patsis et al , 2003(Patsis et al , 2010.…”

Section: Introductionmentioning

confidence: 99%

A Unified Framework for the Orbital Structure of Bars and Triaxial Ellipsoids

Valluri

Shen

Abbott

et al. 2016

ApJ

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We examine a large random sample of orbits in two self-consistent simulations of N-body bars. Orbits in these bars are classified both visually and with a new automated orbit classification method based on frequency analysis. The well-known prograde x1 orbit family originates from the same parent orbit as the box orbits in stationary and rotating triaxial ellipsoids. However, only a small fraction of bar orbits (∼4%) have predominately prograde motion like their periodic parent orbit. Most bar orbits arising from the x1 orbit have little net angular momentum in the bar frame, making them equivalent to box orbits in rotating triaxial potentials. In these simulations a small fraction of bar orbits (∼7%) are long-axis tubes that behave exactly like those in triaxial ellipsoids: they are tipped about the intermediateaxis owingto the Coriolis force, with the sense of tipping determined by the sign of their angular momentum about the long axis. No orbits parented by prograde periodic x2 orbits are found in the pure bar model, but a tiny population (∼2%) of short-axis tube orbits parented by retrograde x4 orbits are found. When a central point mass representing a supermassive black hole (SMBH) is grown adiabatically at the center of the bar, those orbits that lie in the immediate vicinity of the SMBH are transformed into precessing Keplerian orbits thatbelong to the same major families (short-axis tubes, long-axis tubes and boxes) occupying the bar at larger radii. During the growth of an SMBH,the inflow of mass and outward transport of angular momentum transformsome x1 and long-axis tube orbits into prograde short-axis tubes. This study has important implications for future attempts to constrain the masses of SMBHs in barred galaxies using orbit-based methods like the Schwarzschild orbit superposition scheme and for understanding the observed features in barred galaxies.

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“…The role of bars too are now well established in this context. Bars are known to grow via transferring angular momentum outward and eventually goes through the buckling instability to form a boxy/peanut bulges (Combes et al 1990;Raha et al 1991;Athanassoula & Misiriotis 2002;Debattista et al 2004;Saha et al 2010;Saha & Naab 2013). Apart from hosting spiral arms and bars, many disc galaxies are also lopsided (m = 1 perturbation) and generally the asymmetry is prominent in the outer parts of the galaxy.…”

Section: Introductionmentioning

confidence: 99%

Angular momentum transport and evolution of lopsided galaxies

Saha¹,

Jog²

2014

Monthly Notices of the Royal Astronomical Society

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The surface brightness distribution in the majority of stellar galactic discs falls off exponentially. Often what lies beyond such a stellar disc is the neutral hydrogen gas whose distribution also follows a nearly exponential profile at least for a number of nearby disc galaxies. Both the stars and gas are commonly known to host lopsided asymmetry especially in the outer parts of a galaxy. The role of such asymmetry in the dynamical evolution of a galaxy has not been explored so far.Following Lindblad's original idea of kinematic density waves, we show that the outer part of an exponential disc is ideally suitable for hosting lopsided asymmetry. Further, we compute the transport of angular momentum in the combined stars and gas disc embedded in a dark matter halo. We show that in a pure star and gas disc, there is a transition point where the free precession frequency of a lopsided mode, Ω − κ, changes from retrograde to prograde and this in turn reverses the direction of angular momentum flow in the disc leading to an unphysical behaviour. We show that this problem is overcome in the presence of a dark matter halo, which sets the angular momentum flow outwards as required for disc evolution, provided the lopsidedness is leading in nature. This, plus the well-known angular momentum transport in the inner parts due to spiral arms, can facilitate an inflow of gas from outside perhaps through the cosmic filaments.

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A dynamical instability of bars in disk galaxies

Cited by 472 publications

References 12 publications

Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

A Unified Framework for the Orbital Structure of Bars and Triaxial Ellipsoids

Angular momentum transport and evolution of lopsided galaxies

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