Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 781, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/781/1/L20
Keywords
Galaxy: abundances; Galaxy: disk; Galaxy: evolution; Galaxy: formation; Galaxy: kinematics and dynamics; solar neighborhood
Categories
Funding
- Australian Astronomical Observatory
- Leibniz-Institut fur Astrophysik Potsdam (AIP)
- Australian National University
- Australian Research Council
- French National Research Agency
- German Research Foundation [SPP 1177, SFB 881]
- European Research Council [ERC-StG 240271 galactica]
- Istituto Nazionale di Astrofisica at Padova
- Johns Hopkins University
- National Science Foundation of the USA [AST-0908326]
- W. M. Keck foundation
- Macquarie University
- Netherlands Research School for Astronomy
- Natural Sciences and Engineering Research Council of Canada
- Slovenian Research Agency
- Swiss National Science Foundation
- Science & Technology Facilities Council of the UK
- Opticon
- Strasbourg Observatory
- Universities of Groningen, Heidelberg
- Universities of Groningen, Sydney
- STFC [ST/G002509/1, ST/K000977/1, PP/D001242/1, ST/J00149X/1, ST/K00106X/1, ST/G002479/1, ST/K000985/1, PP/D001528/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/G002509/1, ST/K000977/1, ST/G002479/1, ST/K000985/1, PP/D001528/1, PP/D001242/1, ST/H00243X/1, ST/K00106X/1, ST/J00149X/1] Funding Source: researchfish
- UK Space Agency [PP/D006570/1, ST/K00056X/1, ST/I000852/1] Funding Source: researchfish
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The velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine, so a proxy like the abundance of alpha elements (e. g., Mg) with respect to iron, [alpha/Fe], is used. Here we report an unexpected behavior found in the velocity dispersion of a sample of giant stars from the Radial Velocity Experiment survey with high-quality chemical and kinematic information, in that it decreases strongly for stars with [Mg/Fe] > 0.4 dex (i.e., those that formed in the first gigayear of the Galaxy's life). These findings can be explained by perturbations from massive mergers in the early universe, which have affected the outer parts of the disk more strongly, and the subsequent radial migration of stars with cooler kinematics from the inner disk. Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations. Our results suggest that the Milky Way disk merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events.
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