Structure, Kinematics, And Chemical Abundances Of The Inner And Outer Halo Populations
Creators: name: Carollo, Daniela
Publisher: name: Zenodo
Year: 2011
Subjects: Galaxy
Structure
kinematics
Stars
Halo
Chemical abundances

description: PhD Thesis presented for the degree of Doctor of Philosophy of the Australian National University.

Abstract:

The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, which can be used to tightly con-strain models of galaxy formation and evolution.  This thesis presents a wide-ranging analysis of the global structure of the Galactic stellar halo system, comprising the inner and outer halos, through inference of its density profile(s) and determination of the kinematic and orbital parameters of its constituent stars (e.g., mean rotational velocity, velocity ellipsoids, eccentricities). The inner-halo component of the MilkyWay dominates the population of halo stars found at distances up to 10-15 kpc from the Galactic Centre, while the outer-halo component dominates in the regions beyond 15-20 kpc.  It has been shown that stars in the inner-halo population are non-spherically distributed about the centre of the Galaxy,  with an inferred axial ratio on the order of 0.6.  Inner-halo stars possess generally high orbital eccentricities, and exhibit a modest prograde rotation (between 0 and 50 km s-1) around the centre of the Galaxy (Galactocentric rotational velocity).  The metallicity distribution function (MDF) for stars in the inner halo peaks at [Fe/H] = -1.6, with tails extending to higher and lower metallicities.  The outer halo, by contrast, comprises stars that exhibit a much more spherical spatial distribution, with an axial ratio 0.9 to 1.0.  Outer-halo stars cover a wide range of orbital eccentricities,  including many with lower eccentricity orbits than found for most stars associated with the inner halo, and exhibit a clear retrograde net rotation (between -40 and-70 km s-1). The MDF of the outer halo peaks at lower metallicity than that of the inner halo, around [Fe/H] = -2.2, and includes a larger fraction of low-metallicity stars than does the MDF of the inner-halo population. The properties of the thick disk and Metal Weak Thick Disk are also investigated.

In addition, this study addresses the possible chemical distinction between the two halo components in terms of the frequency of the carbon-enhanced metal-poor (CEMP) stars among their membership.
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