OUR MILKY WAY AS A PURE-DISK GALAXY-A CHALLENGE FOR GALAXY FORMATION
- Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China)
- Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, CA (United States)
- Department of Astronomy, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712 (United States)
- Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
Bulges are commonly believed to form in the dynamical violence of galaxy collisions and mergers. Here, we model the stellar kinematics of the Bulge Radial Velocity Assay (BRAVA) and find no sign that the Milky Way contains a classical bulge formed by scrambling pre-existing disks of stars in major mergers. Rather, the bulge appears to be a bar seen somewhat end-on, as hinted from its asymmetric boxy shape. We construct a simple but realistic N-body model of the Galaxy that self-consistently develops a bar. The bar immediately buckles and thickens in the vertical direction. As seen from the Sun, the result resembles the boxy bulge of our Galaxy. The model fits the BRAVA stellar kinematic data covering the whole bulge strikingly well with no need for a merger-made classical bulge. The bar in our best-fit model has a half-length of {approx}4 kpc and extends 20{sup 0} from the Sun-Galactic center line. We use the new kinematic constraints to show that any classical bulge contribution cannot be larger than {approx}8% of the disk mass. Thus, the Galactic bulge is a part of the disk and not a separate component made in a prior merger. Giant, pure-disk galaxies like our own present a major challenge to the standard picture in which galaxy formation is dominated by hierarchical clustering and galaxy mergers.
- OSTI ID:
- 21452838
- Journal Information:
- Astrophysical Journal Letters, Vol. 720, Issue 1; Other Information: DOI: 10.1088/2041-8205/720/1/L72; ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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