ARGOS IV: The kinematics of the Milky Way bulge

Ness, M. and Freeman, K. and Athanassoula, E. and Wylie-de-Boer, E. and Bland-Hawthorn, J. and Asplund, M. and Lewis, G. F. and Yong, D. and Lane, R. R. and Kiss, L. László and Ibata, R. (2013) ARGOS IV: The kinematics of the Milky Way bulge. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 432 (3). pp. 2092-2103. ISSN 0035-8711

Preview

Text 1303.6656v1.pdf Available under License Creative Commons Attribution. Download (788kB) | Preview

Abstract

We present the kinematic results from our ARGOS spectroscopic survey of the Galactic bulge of the Milky Way. Our aim is to understand the formation of the Galactic bulge. We ex- amine the kinematics of about 17,400 stars in the bulge located within 3.5 kpc of the Galactic centre, identified from the 28,000-star ARGOS survey. We aim to determine if the formation of the bulge has been internally driven from disk instabilities as suggested by its boxy shape, or if mergers have played a significant role as expected from ΛCDM simulations. From our velocity measurements across latitudes b = –5◦, –7.5◦ and –10◦ we find the bulge to be a cylindrically rotating system that transitions smoothly out into the disk. Within the bulge, we find a kinematically distinct metal-poor population ([Fe/H ] < −1.0) that is not rotating cylin- drically. The 5% of our stars with [Fe/H] < −1.0 are a slowly rotating spheroidal population, which we believe are stars of the metal-weak thick disk and halo which presently lie in the in- ner Galaxy. The kinematics of the two bulge components that we identified in ARGOS paper III (mean [Fe/H] ≈ –0.25 and [Fe/H] ≈ +0.15, respectively) demonstrate that they are likely to share a common formation origin and are distinct from the more metal-poor populations of the thick disk and halo which are co-located inside the bulge. We do not exclude an underlying merger generated bulge component but our results favour bulge formation from instabilities in the early thin disk.

Actions (login required)

Edit Item