Bibcode
López-Corredoira, M.; Abedi, H.; Garzón, F.; Figueras, F.
Bibliographical reference
Astronomy and Astrophysics, Volume 572, id.A101, 11 pp.
Advertised on:
12
2014
Journal
Citations
37
Refereed citations
36
Description
Aims: We derive the vertical velocities of disk stars in the
range of Galactocentric radii of R = 5 - 16 kpc within 2 kpc in height
from the Galactic plane. This kinematic information is connected to
dynamical aspects in the formation and evolution of the Milky Way, such
as the passage of satellites and vertical resonance and determines
whether the warp is a long-lived or a transient feature. Methods:
We used the PPMXL survey, which contains the USNO-B1 proper motions
catalog cross-correlated with the astrometry and near-infrared
photometry of the 2MASS point source catalog. To improve the accuracy of
the proper motions, the systematic shifts from zero were calculated by
using the average proper motions of quasars in this PPMXL survey, and we
applied the corresponding correction to the proper motions of the whole
survey, which reduces the systematic error. From the color-magnitude
diagram K versus (J - K) we selected the standard candles corresponding
to red clump giants and used the information of their proper motions to
build a map of the vertical motions of our Galaxy. We derived the
kinematics of the warp both analytically and through a particle
simulation to fit these data. Complementarily, we also carried out the
same analysis with red clump giants spectroscopically selected with
APOGEE data, and we predict the improvements in accuracy that will be
reached with future Gaia data. Results: A simple model of warp
with the height of the disk zw(R,φ) = γ(R -
R⊙)sin(φ - φw) fits the vertical
motions if dot {γ }/γ = -34±17 Gyr-1; the
contribution to dot {γ } comes from the southern warp and is
negligible in the north. If we assume this 2σ detection to be
real, the period of this oscillation is shorter than 0.43 Gyr at 68.3%
C.L. and shorter than 4.64 Gyr at 95.4% C.L., which excludes with high
confidence the slow variations (periods longer than 5 Gyr) that
correspond to long-lived features. Our particle simulation also
indicates a probable abrupt decrease of the warp amplitude in a time of
about one hundred Myr. Conclusions: The vertical motion in the
warp apparently indicates that the main S-shaped structure of the warp
is a long-lived feature, whereas the perturbation that produces an
irregularity in the southern part is most likely a transient phenomenon.
But we need higher accuracy in the systematic errors of proper motions
to confirm this tentative detection of vertical motion in the outer
disk. With the use of the Gaia end-of-mission products together with
spectroscopically classified red clump giants, the precision in vertical
motions can be increased by an order of magnitude at least.
Related projects
Morphology and dynamics of the Milky Way
This project consists of two parts, each differentiated but both complementary: morphology and dynamics. Detailed study of the morphology of the Milky Way pretends to provide a data base for the stellar distribution in the most remote and heavily obscured regions of our Galaxy, through the development of semiempirical models based on the
Martín
López Corredoira