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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 710096.0, MPI für Astronomie / Publikationen_mpia
Young stars in an old bulge: A natural outcome of internal evolution in the Milky Way
Authors:Ness, M.; Debattista, V. P.; Bensby, T.; Feltzing, S.; Roskar, R.; Cole, D. R.; Johnson, J. A.; Freeman, K.
Date of Publication (YYYY-MM-DD):2014
Title of Journal:The Astrophysical Journal Letters
Issue / Number:2
Start Page:id. L19 (6 pp)
Audience:Not Specified
Abstract / Description:The center of our disk galaxy, the Milky Way, is dominated by a boxy/peanut-shaped bulge. Numerous studies of the bulge based on stellar photometry have concluded that the bulge stars are exclusively old. The perceived lack of young stars in the bulge strongly constrains its likely formation scenarios, providing evidence that the bulge is a unique population that formed early and separately from the disk. However, recent studies of individual bulge stars using the microlensing technique have reported that they span a range of ages, emphasizing that the bulge may not be a monolithic structure. In this Letter we demonstrate that the presence of young stars that are located predominantly nearer to the plane is expected for a bulge that has formed from the disk via dynamical instabilities. Using an N-body+ smoothed particle hydrodynamics simulation of a disk galaxy forming out of gas cooling inside a dark matter halo and forming stars, we find a qualitative agreement between our model and the observations of younger metal-rich stars in the bulge. We are also able to partially resolve the apparent contradiction in the literature between results that argue for a purely old bulge population and those that show a population comprised of a range in ages; the key is where to look.
Free Keywords:Galaxy: bulge; Galaxy: evolution; Galaxy: formation; Galaxy: stellar content
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-637X %R 10.1088/2041-8205/787/2/L19
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