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Young stars in an old bulge: a natural outcome of internal evolution in the Milky Way

Ness, M.; Debattista, Victor P.; Bensby, Thomas LU ; Feltzing, Sofia LU ; Roskar, R.; Cole, D. R.; Johnson, J. A. and Freeman, K. (2014) In Astrophysical Journal Letters 787(2).
Abstract
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: bulge, Galaxy: evolution, Galaxy: formation, Galaxy: stellar, content
in
Astrophysical Journal Letters
volume
787
issue
2
publisher
University of Chicago Press
external identifiers
  • wos:000336797700004
  • scopus:84901333107
ISSN
2041-8213
DOI
10.1088/2041-8205/787/2/L19
language
English
LU publication?
yes
id
f2c5c612-078b-451e-9682-d49f5e69d154 (old id 4552397)
date added to LUP
2014-07-17 10:40:44
date last changed
2017-10-01 03:09:35
@article{f2c5c612-078b-451e-9682-d49f5e69d154,
  abstract     = {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.},
  articleno    = {L19},
  author       = {Ness, M. and Debattista, Victor P. and Bensby, Thomas and Feltzing, Sofia and Roskar, R. and Cole, D. R. and Johnson, J. A. and Freeman, K.},
  issn         = {2041-8213},
  keyword      = {Galaxy: bulge,Galaxy: evolution,Galaxy: formation,Galaxy: stellar,content},
  language     = {eng},
  number       = {2},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal Letters},
  title        = {Young stars in an old bulge: a natural outcome of internal evolution in the Milky Way},
  url          = {http://dx.doi.org/10.1088/2041-8205/787/2/L19},
  volume       = {787},
  year         = {2014},
}