Research Division Seminar
The impossible Local Group of galaxies (CANCELLED/POSTPONED)
It is well known that the Milky Way and Andromeda have satellite galaxies which lie in thin planes and that these planes are highly correlated. For example, they are rotating in the same sense. Apart from this problem, all the other non-satellite galaxies in the Local Group are in thin (50kpc), extended (1.5Mpc) planes, equidistantly arranged from the Milky Way and from Andromeda. The remaining volume of the Local Group is empty. This ancient symmetrical structure of the Local Group is frightening for any cosmological model. Just outside the Local Group, the nearest 5 galaxies again lie in a 50kpc thick, 1.5Mpc extended plane, which is racing away from the Local Group but could not have escaped from it about 8Gyr ago due to dynamical friction on the various dark matter halos involved. Thus, where we have the very best 3D and velocity information of the arrangement of galaxies, this arrangement appears to be impossible to understand in terms of any currently known physical process. That other groups of galaxies may pose similar challenges is shown by the discovery of the very thin plane of satellites around Cen A, making such system the rule rather than the exception. In summary, real cosmological structure formation appears to lead to a very structured distribution of matter on Mpc scales.
About the talk
Univ. Bonn & Charles University, Prague