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The dual nature of the Milky Way stellar halo

Published online by Cambridge University Press:  12 August 2011

Anna Curir ,
Giuseppe Murante ,
Eva Poglio  and
Álvaro Villalobos
Anna Curir
Affiliation:
INAF-Astronomical Observatory of Torino, strada Osservatorio 20, 10025 Pino Torinese (Torino)Italy email: curir@oato.inaf.it
Giuseppe Murante
Affiliation:
INAF-Astronomical Observatory of Torino, strada Osservatorio 20, 10025 Pino Torinese (Torino)Italy email: curir@oato.inaf.it
Eva Poglio
Affiliation:
Dept. of Physics, Turin University, Italy email: epoglio@studenti.ph.unito.it
Álvaro Villalobos
Affiliation:
INAF - Astronomical Observatory of Trieste, via Tiepolo 11, Trieste, Italy email: villalobos@oats.inaf.it
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Abstract

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The theory of the Milky Way formation, in the framework of the ΛCDM model, predicts galactic stellar halos to be built from multiple accretion events starting from the first structure to collapse in the Universe.

Evidences in the past few decades have indicated that the Galactic halo consists of two overlapping structural components, an inner and an outer halo. We provide a set of numerical N-body simulations aimed to study the formation of the outer Milky Way (MW) stellar halo through accretion events between a (bulgeless) MW-like system and a satellite galaxy. After these minor mergers take place, in several orbital configurations, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions of the mergers where a signal of retrograde rotation in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the MW stellar halo.

Our results show that the dynamical friction has a fundamental role in assembling the final velocity distributions originated by different orbits and that retrograde satellites moving on low inclination orbits deposit more stars in the outer halo regions and therefore can produce the counter-rotating behavior observed in the outer MW halo.

Keywords

Galaxy: formationkinematics and dynamicshalo
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S271: Astrophysical Dynamics: From Stars to Galaxies , June 2010 , pp. 145 - 152
Copyright
Copyright © International Astronomical Union 2011

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