期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 482, 期 3, 页码 3868-3879出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sty2806
关键词
stars: variables: RR Lyrae; Galaxy: kinematics and dynamics; Galaxy: stellar content; Galaxy: structure; galaxies: individual (Milky Way)
资金
- Royal Society Newton International Fellowship
- European Research Council under the European Union [308024]
- European Research Council (ERC) [308024] Funding Source: European Research Council (ERC)
We use the Gaia DR2 RR Lyrae sample to gain an uninterrupted view of the Galactic stellar halo. We dissect the available volume in slices parallel to the Milky Way's disc to show that within similar to 30 kpc from the Galactic centre the halo is triaxial, with the longest axis misaligned by similar to 70 degrees with respect to the Galactic x-axis. This anatomical procedure exposes two large diffuse overdensities aligned with the semimajor axis of the halo: the Hercules-Aquila Cloud and the Virgo overdensity. We reveal the kinematics of the entire inner halo by mapping out the amplitudes and directions of the RR Lyrae proper motions. These are then compared to simple models with different anisotropies to demonstrate that the inner halo is dominated by stars on highly eccentric orbits. We interpret the shape of the density and the kinematics of the Gaia DR2 RR Lyrae as evidence in favour of a scenario in which the bulk of the halo was deposited in a single massive merger event.
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