IAUS379: Dynamical Masses of Local Group Galaxies

The vast multidimensional data observed in the Local Group (LG) provide us with the unique opportunity of comparing the properties of the LG with their simulated analogs in cosmological simulations. In such a comparison it has been found that the observed kinematic properties of satellite galaxies in the LG are very unusual when compared to cosmological simulations. In both the Milky Way and the Andromeda galaxy, satellite galaxies are found to be distributed and moving in flattened co-rotating systems. A configuration that is only found in 0.3-3% of the simulated galaxies. Such disagreement is known as the planes of satellites problem. More intriguing is that the disagreement is persistent even in different dark matter models and unlike other 'small-scale problems' it is not sensitive to the inclusion of baryonic processes in the simulations.

In this talk, I would provide new evidence of how a natural explanation of the observed co-rotation patterns are associated with the out-of-equilibrium state of the galaxy. Recent missions and surveys, such as Gaia, have revealed that the Milky Way galaxy is not in dynamical equilibrium. The barycenter of the galaxy is moving due to the ongoing interaction with the Large Magellanic Cloud. Using the Latte hydrodynamical high-resolution zoom-in simulation of MW-like galaxies A massive satellite moves the reference frame of the inner halo with respect to the outer halo. Resulting in some cases in apparent co-rotation motions of the outer halo when observed from the disk of the galaxies. I'll show how the orbital poles distribution of outer halo objects is strongly affected during the pericenter passages. I will further discuss what properties of the mergers, mass ratios, pericenter passages, and eccentricities, would be needed to reproduce the observational co-rotations pattern observed in the Milky Way and M31.

These results provide new insight into how the observed co-ration patterns can inform us about the out-of-equilibrium stare of the galaxy. Which is a natural explanation that does not depend on the nature of the Dark Matter particle and in baryonic processes. In the talk, I will also discuss the importance of taking into account the dynamic state of the LG when comparing it with LG analogs in cosmological simulations.