THE INNER STRUCTURE AND KINEMATICS OF THE SAGITTARIUS DWARF GALAXY AS A PRODUCT OF TIDAL STIRRING
- Nicolaus Copernicus Astronomical Center, 00-716 Warsaw (Poland)
- Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States)
- Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States)
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
- Institute for Theoretical Physics, University of Zuerich, CH-8057 Zuerich (Switzerland)
The tidal stirring model envisions the formation of dwarf spheroidal (dSph) galaxies in the Local Group and similar environments via the tidal interaction of disky dwarf systems with a larger host galaxy like the Milky Way. These progenitor disks are embedded in extended dark halos and during the evolution both components suffer strong mass loss. In addition, the disks undergo the morphological transformation into spheroids and the transition from ordered to random motion of their stars. Using collisionless N-body simulations, we construct a model for the nearby and highly elongated Sagittarius (Sgr) dSph galaxy within the framework of the tidal stirring scenario. Constrained by the present orbit of the dwarf, which is fairly well known, the model suggests that in order to produce the majority of tidal debris observed as the Sgr stream, but not yet transform the core of the dwarf into a spherical shape, Sgr must have just passed the second pericenter of its current orbit around the Milky Way. In the model, the stellar component of Sgr is still very elongated after the second pericenter and morphologically intermediate between the strong bar formed at the first pericenter and the almost spherical shape existing after the third pericenter. This is thus the first model of the evolution of the Sgr dwarf that accounts for its observed very elliptical shape. At the present time, there is very little intrinsic rotation left and the velocity gradient detected along the major axis is almost entirely of tidal origin. We model the recently measured velocity dispersion profile for Sgr assuming that mass traces light and estimate its current total mass within 5 kpc to be 5.2 x 10{sup 8} M{sub sun}. To have this mass at present, the model requires that the initial virial mass of Sgr must have been as high as 1.6 x 10{sup 10} M{sub sun}, comparable to that of the Large Magellanic Cloud, which may serve as a suitable analog for the pre-interaction, Sgr progenitor.
- OSTI ID:
- 21476715
- Journal Information:
- Astrophysical Journal, Vol. 725, Issue 2; Other Information: DOI: 10.1088/0004-637X/725/2/1516; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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