The Galaxy in the cosmological context

Abstract

A new view on our Galaxy has recently emerged, with large consequences on its formation scenarios. Not only new dwarf satellites have been detected, still orbiting and tidally disrupting, but also a multitude of stellar streams or tidal debris have been observed suggesting the formation of the halo through successive accretions. The large scatter in the age-metallicity relation in the solar neighborhood points towards several accretion episodes, while the chemical evolution of the disk requires a more or less continuous gas infall. The global kinematics and morphology refined by large surveys such as 2MASS suggest the existence of two embedded bars, as is frequently observed in external galaxies. The mass of the central black hole has been refined through stellar proper motions, and is compatible with the M$_{bh}$-$σ$ relation valid for all bulges. The baryonic dark matter is no longer thought to lie in compact objects, and on the contrary, more dark cold gas is revealed by gamma-ray observations. The star forming history can be built, and confronted to numerical models of galaxy evolution both through hierarchical and secular scenarios. Our Galaxy plays thus the role of a prototype to probe galaxy formation theories, and in particular thin and thick disk formation.