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Gravitational scattering of stars and clusters and the heating of the Galactic disk

Gustafsson, Bengt; Church, Ross P. LU ; Davies, Melvyn B. LU and Rickman, Hans (2016) In Astronomy and Astrophysics 593.
Abstract

Context. Could the velocity spread, increasing with time, in the Galactic disk be explained as a result of gravitational interactions of stars with giant molecular clouds (GMCs) and spiral arms? Do the old open clusters high above the Galactic plane provide clues to this question? Aims. We explore the effects on stellar orbits of scattering by inhomogeneities in the Galactic potential due to GMCs, spiral arms and the Galactic bar, and whether high-altitude clusters could have formed in orbits closer to the Galactic plane and later been scattered. Methods. Simulations of test-particle motions are performed in a realistic Galactic potential. The effects of the internal structure of GMCs are explored. The destruction of clusters in GMC... (More)

Context. Could the velocity spread, increasing with time, in the Galactic disk be explained as a result of gravitational interactions of stars with giant molecular clouds (GMCs) and spiral arms? Do the old open clusters high above the Galactic plane provide clues to this question? Aims. We explore the effects on stellar orbits of scattering by inhomogeneities in the Galactic potential due to GMCs, spiral arms and the Galactic bar, and whether high-altitude clusters could have formed in orbits closer to the Galactic plane and later been scattered. Methods. Simulations of test-particle motions are performed in a realistic Galactic potential. The effects of the internal structure of GMCs are explored. The destruction of clusters in GMC collisions is treated in detail with N-body simulations of the clusters. Results. The observed velocity dispersions of stars as a function of time are well reproduced. The GMC structure is found to be significant, but adequate models produce considerable scattering effects. The fraction of simulated massive old open clusters, scattered into orbits with /z/ > 400 pc, is typically 0.5%, in agreement with the observed number of high-altitude clusters and consistent with the present formation rate of massive open clusters. Conclusions. The heating of the thin Galactic disk is well explained by gravitational scattering by GMCs and spiral arms, if the local correlation between the GMC mass and the corresponding voids in the gas is not very strong. Our results suggest that the high-altitude metal-rich clusters were formed in orbits close to the Galactic plane and later scattered to higher orbits. It is possible, though not very probable, that the Sun formed in such a cluster before scattering occurred.

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Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: kinematics and dynamics, Open clusters and associations: individual: M 67, Stars: formation, Sun: evolution
in
Astronomy and Astrophysics
volume
593
pages
19 pages
publisher
EDP Sciences
external identifiers
  • scopus:84989229054
  • wos:000385820100002
ISSN
0004-6361
DOI
10.1051/0004-6361/201423916
language
English
LU publication?
yes
id
53465100-f6d7-4ff3-88dd-49bb6fe2d0c2
date added to LUP
2016-11-28 13:10:19
date last changed
2017-07-30 05:17:59
@article{53465100-f6d7-4ff3-88dd-49bb6fe2d0c2,
  abstract     = {<p>Context. Could the velocity spread, increasing with time, in the Galactic disk be explained as a result of gravitational interactions of stars with giant molecular clouds (GMCs) and spiral arms? Do the old open clusters high above the Galactic plane provide clues to this question? Aims. We explore the effects on stellar orbits of scattering by inhomogeneities in the Galactic potential due to GMCs, spiral arms and the Galactic bar, and whether high-altitude clusters could have formed in orbits closer to the Galactic plane and later been scattered. Methods. Simulations of test-particle motions are performed in a realistic Galactic potential. The effects of the internal structure of GMCs are explored. The destruction of clusters in GMC collisions is treated in detail with N-body simulations of the clusters. Results. The observed velocity dispersions of stars as a function of time are well reproduced. The GMC structure is found to be significant, but adequate models produce considerable scattering effects. The fraction of simulated massive old open clusters, scattered into orbits with /z/ &gt; 400 pc, is typically 0.5%, in agreement with the observed number of high-altitude clusters and consistent with the present formation rate of massive open clusters. Conclusions. The heating of the thin Galactic disk is well explained by gravitational scattering by GMCs and spiral arms, if the local correlation between the GMC mass and the corresponding voids in the gas is not very strong. Our results suggest that the high-altitude metal-rich clusters were formed in orbits close to the Galactic plane and later scattered to higher orbits. It is possible, though not very probable, that the Sun formed in such a cluster before scattering occurred.</p>},
  articleno    = {A85},
  author       = {Gustafsson, Bengt and Church, Ross P. and Davies, Melvyn B. and Rickman, Hans},
  issn         = {0004-6361},
  keyword      = {Galaxy: kinematics and dynamics,Open clusters and associations: individual: M 67,Stars: formation,Sun: evolution},
  language     = {eng},
  month        = {09},
  pages        = {19},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {Gravitational scattering of stars and clusters and the heating of the Galactic disk},
  url          = {http://dx.doi.org/10.1051/0004-6361/201423916},
  volume       = {593},
  year         = {2016},
}