Tracing the long bar with red-clump giants

¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain e-mail: antonio.cabrera@gtc.iac.es
² GTC Project Office, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain

Received: 4 August 2006
Accepted: 20 January 2007

Abstract

Context.Over the last decade a series of results have lent support to the hypothesis of the existence of a long thin bar in the Milky Way with a half-length of 4.5 kpc and a position angle of around 45°. This is apparently a very different structure from the triaxial bulge of the Galaxy.

Aims.In this paper, we analyse the stellar distribution in the inner 4 kpc of the Galaxy to see if there is clear evidence for two triaxial or barlike structures, or whether there is only one.

Methods.By using the red-clump population as a tracer of the structure of the inner Galaxy we determine the apparent morphology of the inner Galaxy. Star counts from 2MASS are used to provide additional support for this analysis.

Results.We show that there are two very different large-scale triaxial structures coexisting in the inner Galaxy: a long thin stellar bar constrained to the Galactic plane () with a position angle of 430 ± 18, and a distinct triaxial bulge that extends to at least with a position angle of 126 ± 32. The scale height of the bar source distribution is around 100 pc, whereas for the bulge the value of this parameter is five times larger.