The Morphology of the Milky Way

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Figure 1:The density map and contours of the R~7.3 kpc 2MASS red giant sample. One can trace by eye the warp signature. Over-plotted is also the location of the mean mid-plane warped disk as a function of longitude.

Characterizing the global Milky Way morphology is of fundamental importance in re-constructing its early formation epoch, particularly during the period of accretion of dwarf galaxies, which are thought to be the building blocks of massive galaxies.   In a recently published paper (Momany, Zaggia, Gilmore et al. 2006 link see also the A&A and INAF press release), we used the 2MASS catalogue covering the entire disk regions. We re-constructed the disk overall shape, focusing on the properties of warp (a downward bending in the first 2 quadrant and upward bending the second 2 quadrant) and flare (increasing disk thickness as a function of distance from the Galactic center).

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Figure 2:The upper left panel displays the stellar warp as derived from 2MASS red giants at R~7.3kpc. In the lower left panel we compare the derived warp with those based on two red clump samples between 6

The resulting picture is one in which a strong warp signature is being observed already in the solar circle, and is detectable out to 24 Kpc from the Galactic center. Interestingly, the amplitude and phase-angle of this stellar-based derived warp show excellent agreement with the ones derived for the Milky Way interstellar dust and neutral atomic hydrogen. This agreement argues against recent claims that a dwarf galaxy is now being accreted in the Milky Way disk (the Canis Major dwarf galaxy). 

People: Y. Al Momany, S. Zaggia

Collaboration: G. Gilmore, F. De Angeli (Cambridge, UK), M. Lopez-Corredoira (Ins. de Astrofísica de Canarias, Spain), G. Piotto, G. Carraro (Padova Univ.)

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