Issue |
A&A
Volume 487, Number 3, September I 2008
|
|
---|---|---|
Page(s) | 951 - 963 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20079240 | |
Published online | 06 May 2008 |
Global properties of the H I distribution in the outer Milky Way
Planar and extra-planar gas
Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: [pkalberla;ldedes]@astro.uni-bonn.de
Received:
13
December
2007
Accepted:
31
March
2008
Context. The determination of the global structure of the planar and extra-planar
Milky Way disk depends critically on a reliable database but also on
reasonable assumptions about the shape of the Milky Way rotation curve.
Aims. We derive the 3D volume density distribution for the Galactic disk out to
kpc.
Methods. Our analysis is based on parameters for the warp and rotation curve derived previously. The data are taken from the Leiden/Argentine/Bonn all sky 21 cm line survey.
Results. The Milky Way disk is significantly warped but shows a coherent
structure out to
kpc. The radial surface density distribution,
the densities in the middle of the warped plane, and the
scale
heights all follow exponential relations. The radial scale length for the
surface density distribution of the
disk is 3.75 kpc. Gas at the
outskirts for
kpc is described best by a distribution
with an exponential radial scale length of 7.5 kpc and a velocity
dispersion of 74 km s-1. Such a highly turbulent medium fits also well with
the average shape of the high velocity profile wings observed at high
latitudes. The turbulent pressure gradient of such extra-planar gas is
on average in balance with the gravitational forces. About 10% of the
Milky Way
gas is in this state. The large scale
distribution is
lopsided; for
kpc there is more gas in the south. The
flaring indicates that this asymmetry is caused by a dark matter wake,
located at
kpc in direction of the Magellanic System.
Conclusions. The disk is made up of two major components. Most prominent is the
normal
disk which can be traced to
kpc. This is surrounded
by a patchy distribution of highly turbulent gas reaching large scale
heights but also large radial distances. At the position of the Sun the
exponential scale height in the z direction is 3.9 kpc. This component
resembles the anomalous gas discovered previously in some galaxies.
Key words: Galaxy: disk / Galaxy: halo / Galaxy: structure / Galaxy: kinematics and dynamics / ISM: structure
© ESO, 2008
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