期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 442, 期 3, 页码 2474-2486出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stu1003
关键词
methods: numerical; galaxies: formation; galaxies: kinematics and dynamics; galaxies: structure
资金
- Humboldt Research Fellowship
- Beckwith Trust
We study seven simulated disc galaxies, three with a quiescent merger history, and four with mergers in their last 9 Gyr of evolution. We compare their structure at z = 0 by decomposing them into 'mono-age populations' (MAPs) of stars within 500 Myr age bins. All studied galaxies undergo a phase of merging activity at high redshift, so that stars older than 9 Gyr are found in a centrally concentrated component, while younger stars are mostly found in discs. We find that most MAPs have simple exponential radial and vertical density profiles, with a scaleheight that typically increases with age. Because a large range of merger histories can create populations with simple structures, this suggests that the simplicity of the structure of mono-abundance populations observed in the Milky Way by Bovy et al. is not necessarily a direct indicator of a quiescent history for the Milky Way. Similarly, the anticorrelation between scalelength and scaleheight does not necessarily imply a merger-free history. However, mergers produce discontinuities between thin and thick disc components, and jumps in the age-velocity relation. The absence of a structural discontinuity between thin and thick disc observed in the Milky Way would seem to be a good indicator that no merger with a mass ratio larger than 1:15-1:10 occurred in the last 9 Gyr. Mergers at higher redshift might nevertheless be necessary to produce the thickest, hottest components of the Milky Way's disc.
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