Searching for the in-plane Galactic bar and ring in DENIS

Free access article

Issue		A&A Volume 373, Number 1, July I 2001


Page(s)		139 - 152
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20010560

A&A 373, 139-152 (2001)
DOI: 10.1051/0004-6361:20010560

Searching for the in-plane Galactic bar and ring in DENIS

M. López-Corredoira¹, P. L. Hammersley¹, F. Garzón^{1, 2}, A. Cabrera-Lavers¹, N. Castro-Rodríguez¹, M. Schultheis³ and T. J. Mahoney¹

¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
² Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
³ Institut d'Astrophysique de Paris, 75014 Paris, France

(Received 21 February 2001 / Accepted 10 April 2001)

Abstract
New evidence for a long thin Galactic bar (in contradistinction to the bulge), as well as for the existence of the ring and the truncation of the inner disc, are sought in the DENIS survey. First, we examine DENIS and Two Micron Galactic Survey star counts for the characteristic signatures of an in-plane bar and ring. The star counts in the plane for $30^\circ> l> -30^\circ$ are shown to be highly asymmetric with considerably more sources at positive than at negative longitudes. At $\vert b\vert\approx 1.5^\circ$ , however, the counts are nearly symmetric. Therefore, the asymmetry is not due to the disc, which is shown to have an inner truncation, or to the bulge, so there has to be another major component in the inner Galaxy that is causing the asymmetries. This component provides up to 50% of the detected sources in the plane between the bulge and $l=27^\circ$ or $l=-14^\circ$ . This component is shown to be consistent with an in-plane bar with a position angle of $40^\circ$ and half-length of 3.9 kpc. However, there is also a major peak in the counts at $l=-22^\circ$ , which coincides with the tangential point of the so-called 3 kpc arm. This is shown to be most probably a ring or a pseudo-ring. The extinction in the plane is also shown to be asymmetric with more extinction at negative than at positive longitudes. For $l< 8^\circ$ the extinction is shown to be slightly tilted with respect to $b=0^\circ$ in the same manner as the HI disc. We conclude that the Galaxy is a fairly typical ringed barred spiral galaxy.

Key words: Galaxy: general -- Galaxy: stellar content -- Galaxy: structure -- infrared: stars

Offprint request: M. López-Corredoira, martinlc@ll.iac.es

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