Stellar diffusion in barred spiral galaxies

Abstract

We characterize empirically the radial diffusion of stars in the plane of a typical barred disk galaxy by calculating the local spatial diffusion coefficient and diffusion time-scale for bulge-disk-halo N-body self-consistent systems which initially differ in the SafronovToomre-Q T parameter. We find different diffusion scenarios that depend on the bar strength and on the degree of instability of the disk. Marginally stable disks, with Q T ∼ 1, have two families of bar orbits with different values of angular momentum and energy, which determine a large diffusion in the corotation region. In hot disks, Q T > 1, stellar diffusion is reduced with respect to the case of marginally stable disks. In cold models, we find that spatial diffusion is not constant in time and strongly depends on the activity of the bar, which can move stars all over the disk recurrently. We conclude that to realistically study the impact of radial migration on the chemical evolution modeling of the Milky Way the role of the bar has to be taken into account.

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

“…This is surprising in view of the theory developed by Sellwood & Binney (2002), where the CR is effective only if structure is transient. This is consistent with the findings of Brunetti et al (2011).…”

“…This fact renders the bars in our simulations the most effective drivers of radial migration, despite the fact that they are not transient, but only slowly evolving. This is surprising in view of the theory developed by Sellwood & Binney (2002), where the CR is effective only if structure is transient, but agrees with the work by Brunetti et al (2011) and Minchev et al (2012c).…”

“…We showed that although asymmetries developed later (well after the initial relaxation) when a higher number of particles was employed, the overall results were in agreement. This means that independently of the initial relaxation of the system, it is the appearance and presence of strong stellar asymmetries that drives migration (also in agreement with Brunetti et al 2011).…”

Constraining the Milky Way assembly history with Galactic Archaeology

“…In such a setup angular momentum redistribution arises from the overlap of resonances associated with different modes or from the stellar mass transiency as perturbers with different pattern speeds interfere constructively (see Comparetta & Quillen 2012), but not from the growth and decay of transient modes. This work, along with studies of diffusion coefficients in barred discs (Brunetti et al 2011;Shevchenko 2011), predicts a variation in migration efficiency with time and disc radius, establishing that the dynamical influence of the bar plays an integral part of Milky Way disc modeling. Aside from internal structure, pertur-bations due to minor mergers have also been shown to be effective at mixing the outer discs (Bird et al 2012;Quillen et al 2009), but also can, indirectly, affect the entire disc by inducing (reinforcing) spiral and bar instabilities (e.g., Purcell et al 2011).…”

“…The formation of galactic thick discs has been an important topic ever since their discovery in external galaxies (Burstein 1979;Tsikoudi 1979) and in the Milky Way (Gilmore & Reid 1983). The large uncertainties in important observational constraints in the Milky Way, such as the agevelocity-metallicity relation, abundance gradients and their evolution, have led to different scenarios to be proposed for the formation of the Galactic thick disc.…”