Talk detail

Participant	Pawlowski, Marcel
Institution	Argelander Institute for Astronomy, University of Bonn - Auf dem Huegel 71 - Bonn - NRW - Germany

Session	EG4	Accepted	Yes	Order	9	Time	16:30 - 16:45
Talk	Oral abstract	Title	The Vast Polar Structure of the Milky Way and filamentary accretion of dark matter sub-halos
Co-authors
Abstract	The Milky Way (MW) is surrounded by numerous satellites: dwarf galaxies, globular clusters and streams of disrupted systems. I will show that the 'classical' (bright) satellite galaxies, the faint ones detected in the SDSS and globular clusters classified as young halo objects are all unevenly distributed. Each sample can be described by essentially the same plane, highly inclined to the Galactic disc. Together, these objects form a vast polar structure (VPOS), spreading from Galactocentric distances as small as 10 kpc out to 250 kpc. The orbital directions of satellite galaxies and the orientations of streams show that the objects preferentially orbit within this plane. This observed, highly correlated phase-space distribution is at odds with the expectations from cosmological simulations of structure formation based on cold-dark matter. An independent infall of cosmological sub-structure components onto the MW is essentially ruled out. The infall of a group of dwarf galaxies has also been shown not to reproduce the observed anisotropy. In the last attempt, the accretion of sub-halos along filaments is claimed to be the origin of the observed distribution, but so far publications claiming this did not test the scenario. We have performed such a test, using high-resolution cosmological simulations. It shows that filamentary accretion can not account for the large degree of correlation of the MW satellite orbits. I will motivate further arguments against this explanation and, in the end, briefly discuss a very natural alternative formation scenario of the observed VPOS.