Two stellar components in the halo of the Milky Way

Date

2007

Authors

Carollo, Daniela
Beers, Timothy C.
Lee, Young Sun
Chiba, Masahi
Norris, John
Wilhelm, Ronald
Sivarani, T.
Marsteller, Brian
Munn, Jeffrey A.
Bailer-Jones, C. A. L.

Journal Title

Journal ISSN

Volume Title

Publisher

Macmillan Publishers Ltd

Abstract

The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components - an inner and an outer halo - that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.

Description

Keywords

Keywords: helium; hydrogen; iron; abundance; astronomy; evolution; article; astronomy; cosmos; kinematics; priority journal; space

Citation

Source

Nature

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

DOI

10.1038/nature06460

Restricted until

2037-12-31