Simulating the galactic system in interaction AM 2229-735 and the formation of its polar structure

We study the formation of polar ring galaxies via minor mergers. We used N-body+hydrodynamics simulations to reproduce the dynamics of the observed system AM 2229-735 that is a minor merger whose interaction signals are those of a progenitor for a polar ring galaxy. We used the observational information of the system to get initial conditions for the orbit and numerical realisations of the galaxies to run the simulations. Our simulations reproduce the global characteristics of interaction observed in the system such as arms and a material bridge connecting the galaxies. As a merger remnant, we found a quasi-stable and self gravitating planar tidal stream with dark matter, stars and gas orbiting in a plane approximately perpendicular to the main galaxy disk leading in the future to a polar ring galaxy. We studied the dynamical conditions of the polar structure and found evidence suggesting that this kind of merger remnant can settle down in a disk-like structure with isothermal support, providing inspiring evidence about the process of formation of galactic disks and providing a potentially independent scenario to study the presence of dark matter in this kind of galaxies.

Connecting interacting galaxies with manifolds

It is well known that the interaction between two disk galaxies generates tidal spiral arms and a connection in the form of a bridge. Here we address the question of the formation of tidal arms and bridges from a dynamical point of view. We model the bridges and tails observed in interacting galaxies using the invariant manifolds associated to the Lyapunov orbits of the Lagrangian points of the galactic system, when the two galaxies are considered as two point masses in a circular orbit.

DIVISION H COMMISSION 33: STRUCTURE & DYNAMICS OF THE GALACTIC SYSTEM

Research on the structure and dynamics of the Galactic System covers a large field of research, from formation scenarios to long-term evolution and secular processes. Today we speak of near-field cosmology where the oldest parts of the Galaxy are used to probe back to early times, e.g. studying the chemical signatures of the oldest star clusters and dwarf galaxies to learn about the byproducts of the first stars. Some of the most detailed work relates to the structure of the dark matter and baryons in order to compare with expectation from N-body models. Secular processes have been identified (e.g. stellar migration) where material within the Galaxy is being reorganized by dynamical resonances and feedback processes.

ANISOTROPY OF COSMIC ACCELERATION

In this paper, we study the anisotropy of cosmic acceleration by dividing the Union2 Type Ia supernova (SNIa) dataset into 12 subsets according to their positions in Galactic coordinate system. In each region, we derive the deceleration parameter q0 as the diagnostic to quantify the anisotropy level in the corresponding direction, and construct q0 anisotropic maps by combining these q0 values. In addition to the monopole component, we find the significant dipole effect in the q0-maps with the amplitude [Formula: see text], which deviates from zero at more than 2-σ level. The direction of the best-fit dipole is (θ = 108.8°, ϕ = 187.0°) in Galactic system. Interesting enough, we find the direction of this dipole is nearly perpendicular to the CMB kinematic dipole, and the angle between them is 95.7°. The perpendicular relation is anomalous at the 1-in-10 level.

DIVISION VII: THE GALACTIC SYSTEM

Division VII provides a forum for astronomers studying the Milky Way Galaxy and its constituents. Several meetings directly relevant to his subject were held at the General Assembly in Rio: IAU Symp. 262 Stellar Populations, IAU Symp. 265 Chemical Abundances in the Universe, IAU Symp. 266 Star Clusters, Joint Discussion 5 Modeling the Milky Way in the Era of Gaia, and Special Session 5 The Galactic Plane. Division VII therefore did not organize a separate science session at Rio, but business meetings were held for both the Division and for Commissions 33 and 37.

COMMISSION 33: STRUCTURE AND DYNAMICS OF THE GALACTIC SYSTEM

Commission 33 held its business session in the afternoon of Friday 7 August 2009. The president briefly described developments during the previous months. A short discussion followed about the activities of the Commission and whether it should play a more active role in view of the many on-going surveys relevant to the subject of the Galaxy.