On the Tidal Radius of Satellites on Prograde and Retrograde Orbits

2016

ApJ

Self Cite

Orbits are the key building blocks of any density distribution and their study helps us understand the kinematical structure and the evolution of galaxies. Here we investigate orbits in a tidally induced bar of a dwarf galaxy, using an N -body simulation of an initially disky dwarf galaxy orbiting a Milky Way-like host. After the first pericenter passage, a tidally induced bar forms in the stellar component of the dwarf. The bar evolution is different than in isolated galaxies and our analysis focuses on the period before it buckles. We study the orbits in terms of their dominant frequencies, which we calculate in a Cartesian coordinate frame rotating with the bar. Apart from the well-known x 1 orbits we find many other types, mostly with boxy shapes of various degree of elongation. Some of them are also near-periodic, admitting frequency ratios of 4/3, 3/2 and 5/3. The box orbits have various degrees of vertical thickness but only a relatively small fraction of those have banana (i.e. smile/frown) or infinity-symbol shapes in the edge-on view. In the very center we also find orbits known from the potential of triaxial ellipsoids. The elongation of the orbits grows with distance from the center of the bar in agreement with the variation of the shape of the density distribution. Our classification of orbits leads to the conclusion that more than 80% of them have boxy shapes, while only 8% have shapes of classical x 1 orbits.

Section: The Simulationsupporting

confidence: 55%

The Orbital Structure of a Tidally Induced Bar

Gajda

Łokas

2016

ApJ

Self Cite

“…However, haloes in our simulations are heavily stripped at all radii and heavily perturbed. On the fiducial orbit, the size of the halo drops from 6 kpc after the first pericenter to 3 kpc at the end, as can be estimated from the break in the dark matter density profile (see Figure 1 in Gajda & Lokas 2016). Moreover, the halos lose mass also from the inner parts.…”

Section: Angular Momentum and Corotationmentioning

confidence: 93%

“…retrograde) angular momentum. This is a direct result of the preferential stripping of particles on prograde orbits, in contrast to the retrograde ones (Hénon 1970;Gajda & Lokas 2016, and references therein). The spikes appearing just after the pericenter passages are due to the disturbance by the tidal force.…”

Section: Angular Momentum Transfermentioning

confidence: 97%

Tidally Induced Bars in Dwarf Galaxies on Different Orbits around a Milky Way-like Host

Gajda

Łokas

2017

ApJ

Self Cite

Bars in galaxies may develop through a global instability or due to an interaction with another system. We study bar formation in disky dwarf galaxies orbiting a Milky Way-like galaxy. We employ N -body simulations to study the impact of initial orbital parameters: the size of the dwarf galaxy orbit and the inclination of its disc with respect to the orbital plane. In all cases a bar develops in the center of the dwarf during the first pericenter on its orbit around the host. Between subsequent pericenter passages the bars are stable, but at the pericenters they are usually weakened and shortened. The initial properties and details of the further evolution of the bars depend heavily on the orbital configuration. We find that for the exactly prograde orientation, the strongest bar is formed for the intermediate-size orbit. On the tighter orbit, the disc is too disturbed and stripped to form a strong bar. On the wider orbit, the tidal interaction is too weak. The dependence on the disc inclination is such that weaker bars form in more inclined discs. The bars experience either a very weak buckling or none at all. We do not observe any secular evolution, possibly because the dwarfs are perturbed at each pericenter passage. The rotation speed of the bars can be classified as slow (R CR /l bar ∼ 2 − 3). We attribute this to the loss of a significant fraction of the disc's rotation during the encounter with the host galaxy.

“…More recently, numerical experiments suggest a dwarf-dwarf galaxy interaction origin for the offset bar and one-arm structure (Besla et al 2012;Yozin & Bekki 2014). The tidal interactions between dwarf galaxies with different masses play a key role in the stellar and gas stripping in low-mass systems as a consequence of resonant interactions between spinning disks (D'Onghia et al 2009Gajda & Lokas 2015;Łokas et al 2015) and explain the morphology and the origin of the Magellanic Stream (Besla et al 2010(Besla et al , 2012.…”

Section: Introductionmentioning

confidence: 99%

Tidally Induced Offset Disks in Magellanic Spiral Galaxies

Pardy¹,

D’Onghia²,

et al. 2016

ApJ

Magellanic spiral galaxies are a class of one-armed systems that often exhibit an offset stellar barand are rarely found around massive spiral galaxies. Using a set of N-body and hydrodynamic simulations, we consider a dwarfdwarf galaxy interaction as the driving mechanism for the formation of this peculiar class of systems. We investigate here the relation between the dynamical, stellar, and gaseous disk center and the bar. In all our simulations the bar center always coincides with the dynamical center, while the stellar disk becomes highly asymmetric during the encounter, causing the photometric center of the Magellanic galaxy disk to become mismatched with both the bar and the dynamical center. The disk asymmetries persist for almost 2 Gyr, the time that it takes for the disk to be recentered with the bar, and well after the companion has passed. This explains the nature of the offset bar found in many Magellanic-type galaxies, including the Large Magellanic Cloud (LMC) and NGC 3906. In particular, these results, once applied to the LMC, suggest that the dynamical center should reside in the bar center instead of the H I center as previously assumed, pointing to a variation in the current estimate of the north component of the LMC proper motion.