A&A press release: Deriving the shape of the Galactic stellar disc (16 March 2006)
- Published on 16 March 2006
A&A press release
Released on March 16th, 2006
Deriving the shape of the Galactic stellar disc
Based on the article “Outer structure of the Galactic warp and flare: explaining the Canis Major over-density”, by Y. Momany et al.
(To be published in Astronomy & Astrophysics. )
This press release is issued as a collaboration with the Italian Institute for Astrophysics (INAF) and Astronomy & Astrophysics.
Using the 2MASS all-sky near infrared catalogue, Yazan Momany and his collaborators reconstructed the outer structure of the Galactic stellar disc, in particular, its warp. Their work will soon be published in Astronomy & Astrophysics. Observationally, the warp is a bending of the Galactic plane upwards in the first and second Galactic longitude quadrants (0<l<180 degrees) and downwards in the third and fourth quadrants (180<l<360 degrees). Although the origin of the warp remains unknown, this feature is seen to be a ubiquitous property of all spiral galaxies. As we are located inside the Galactic disc, it is difficult to unveil specific details of its shape. To appreciate a warped stellar disc one should, therefore, look at other galaxies. Figure 1 shows a good example of what a warped galaxy looks like.
The new analysis by Momany and his team provides the first clear and complete view of the outer stellar disc warp. They analyzed the distribution of over 115 million stars from the all-sky 2MASS catalogue that comprise the totality of the Galactic disc. Among the many different stellar types, M-giant stars were found to be the ideal stellar tracer for reconstructing the outer disc structure. They are, in fact, highly luminous but relatively cool and evolved stars, and these unique properties allow better determination of their distance. The analysis also shows that M-giants stars located at distances between 3,000 and of 17,000 pc from the Sun draw the same stellar warp signature. This means that a global and large-scale Milky Way feature has been identified to about 25,000 pc from the Galactic centre: the team thus clearly demonstrates that there is no truncation of the stellar disc beyond 14,000 pc. The figures below illustrate the shape of the Galactic outer stellar disc. Figure 2 shows the density maps as derived from the 2MASS M-giant sample at 14,000 pc from the Galactic centre. The presence of the warp is quite clear at both ends of the stellar disc. Figure 3 quantitatively shows the amplitude and orientation of the disc’s stellar warp as a function of the Galactic longitude. It also shows the consistency of the warp signature in the three disc components (gas, dust, and stars). It is a natural consequence of the close physical correlation between these three Galactic disc components, and proves once more the existence of a global and regular warp signature for the Galactic disc.
 The team includes Y. Momany, S. Zaggia, G.P. Piotto (Italy), G. Gilmore, F. De Angeli (United Kingdom), G. Carraro (Chile) and L. Bedin (Germany).
Outer structure of the Galactic warp and flare: explaining the Canis Major over-density, by Y. Momany, S. Zaggia, G. Gilmore, G.P. Piotto, G. Carraio, L. Bedin & F. De Angeli.
To be published in Astronomy & Astrophysics (DOI number: 10.1051/0004-6361:20054081)
Dr. Momany Yazan
Email: momany (at) pd.astro.it
Phone: +39 340 6156797
Dr. Zaggia Simone
Email: zaggia (at) oats.inaf.it
Phone: +39 040 3199212
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