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The Milky Way in a cosmological context : finding the good dark halo

Proposition de stage au niveau M1.

Proposants : Paola Di Matteo (GEPI), Revaz Yves (Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne)

Subject : Galactic research has entered a thrilling epoch. Our knowledge of Galactic stellar populations, until few years ago mostly confined to stars at the solar vicinity, is rapidly extending to large regions of the disc and bulge of our Galaxy. Large spectroscopic surveys are acquiring an unprecedented amount of data, with radial velocities and chemical composition for hundred thousands stars, from the innermost regions to the periphery of the Milky Way disc, up to 15 kpc from the Galactic center. This unique, because unprecedented, cartography of our Galaxy will acquire all its potential with the publication of the data from Gaia, the European astrometric mission, which will deliver positions and proper motions for 1 billion objects, and radial velocities for about one tenth of them. The tremendous amount of data that the mission will deliver will need efficient tools for their analysis but also sophisticated models for their interpretation. We are interested to answer to some of the simplest but still unraveled questions of Galactic studies : What are the characteristics of the different Milky Way stellar populations ? How were they shaped over time ? What is the evolutionary link between them ? Which of them is the result of in-situ star formation or rather the deposit of structures accreted over time ?

In this internship, we propose to start answering some of these questions by analyzing a large volume cosmological N-body simulation developed by Yves Revaz, at the Ecole Polytechnique Fédérale de Lausanne, Switzerland. This simulation contains dark matter only, and no baryonic physics is included. The aim of this analysis is to select “good host halos” for the Milky Way, that is dark halos with masses and accretion histories compatible to what is expected for our Galaxy. Once a set of appropriate halos is selected, high resolution cosmological-zoom simulations including baryonic physics - with star formation and detailed chemical evolution - will be run.

The interested student will learn how to analyze the pure dark matter cosmological simulation, and possibly - depending on performances - she/he will also help in settling the scene for the cosmological-zoom simulations.