Thomas Bensby
Senior lecturer
Young stars in an old bulge: a natural outcome of internal evolution in the Milky Way
Author
Summary, in English
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.
Department/s
- Lund Observatory - Has been reorganised
Publishing year
2014
Language
English
Publication/Series
Astrophysical Journal Letters
Volume
787
Issue
2
Document type
Journal article
Publisher
IOP Publishing
Topic
- Astronomy, Astrophysics and Cosmology
Keywords
- Galaxy: bulge
- Galaxy: evolution
- Galaxy: formation
- Galaxy: stellar
- content
Status
Published
ISBN/ISSN/Other
- ISSN: 2041-8213