A New Mechanism for Radial Migration in Galactic Disks: Spiral-Bar Resonance Overlap

Abstract

While it has long been known that a large number of short-lived transient spirals can cause stellar migration, here we report that another mechanism is also effective at mixing disks of barred galaxies. The resonance overlap of the bar and spiral structure induces a nonlinear response leading to a strong redistribution of angular momentum in the disk. We find that, depending on the amplitudes of the perturbers, the changes in angular momentum, ∆L, could occur up to an order of magnitude faster than in the case of recurrent spirals. The signature of this mechanism is a bimodality in ∆L with maxima near the bar's corotation and its outer Lindblad resonance; this is independent of the properties of the spiral structure. For parameters consistent with the Milky Way the disk mixes in about 3 Gyr and the stellar velocity dispersion increases with time in a manner roughly consistent with observations. This new mechanism could account for both the observed age-velocity relation and the absence of age-metallicity relation in the solar neighborhood. Spiral-bar interaction could also explain observations showing that strongly barred galaxies have weaker metallicity gradients than weakly barred or non-barred galaxies.

Radial migration of the Sun in the Milky Way: a statistical study

“…As we mentioned in the introduction, if the Sun is indeed not more metal rich than the stars of its same age and Galactocentric radius it is probable that the Sun has not experienced considerable migration over its lifetime. Minchev & Famaey (2010) studied the effects of the bar-spiral arm resonance overlap in the solar neighborhood. They found that a large fraction of stars that were located initially at inner and outer regions of the Galactic disk, ended up at a distance of ∼ 8 kpc after 3 Gyr of evolution.…”

“…This explains the observed lack of a metallicity gradient with age in the solar neighborhood (Haywood 2008); however, the same simulations show that after 3 Gyr of evolution, the peak of the initial radial distribution of stars that end up at 8 kpc is also around 8 kpc, meaning that most of the stars at solar radius, do not migrate. For their simulations, Minchev & Famaey (2010) modelled the central bar and spiral arms of the Galaxy as non-transient perturbations.…”

“…It has been demonstrated by Minchev & Famaey (2010) and Minchev et al (2011) that the dynamical effects of overlapping resonances from the bar and spiral arms provide an efficient mechanism for radial migration in galaxies. Depending of the strength of the perturbations, radial mixing in Galactic disks proceeds up to an order of magnitude faster than in the case of transient spiral arms.…”

“…However, the gravitational non-axisymmetric perturbations such as the central bar and spiral arms, rotate as rigid bodies. In consequence, stars at different radii will experience different forcing due to these non-axisymmetric structures (Minchev & Famaey 2010). There are specific locations in the Galactic disk where stars are in resonance with the perturbations.…”

The evolution of the Milky Way: new insights from open clusters

“…The larger changes in angular momentum of stars (churning) always occur near the corotation resonance that leads to the radial migration of stars of few kpc from their birth radii on a short period, while the effect at the inner/outer Lindblad resonances (blurring) is smaller (Sellwood & Binney 2002;Minchev & Famaey 2010). Through N-body simulations, Fujii & Baba (2012) find that clusters lose (gain) at most 50% of their angular momentum within 1 Gyr.…”