Stellar density distribution in the NIR on the Galactic plane at longitudes 15–27 deg. Clues for the Galactic bar?

Abstract

Abstract. Garzón et al. (1997), López-Corredoira et al. (1999) and Hammersley et al. (2000) have identified in TMGS and DENIS data a large excess of stars at l = 27• and b = 0 • which might correspond to an in-plane bar. We compared near infrared CAIN star counts and simulations from the Besançon Model of Galaxy on 15 fields between 15• and 45• in longitude and −2• and 2• in latitude. Comparisons confirm the existence of an overdensity at longitudes lower than 27• which is inhomogeneous and decreases very steeply off the Galactic plane. The observed excess in the star distribution over the predicted density is even higher than 100%. Its distance from the sun is estimated to be lower than 6 kpc. If this overdensity corresponds to the stellar population of the bar, we estimate its half-length to 3.9 ± 0.4 kpc and its angle from the Sun-center direction to 45 ± 9 degrees.

Tracing the long bar with red-clump giants

“…5.3), as this line of sight does run close to a major star formation region (Garay et al 1998;Sridharan et al 2005). Furthermore, the over-density is is apparently somewhat inhomogeneous, as was noted by Picaud et al (2003) at l = 20…”

“…López-Corredoira et al (2002) developed a method to obtain the star density and interstellar extinction along a line of sight by extracting the red-clump population from the NIR colour-magnitude diagrams (CMDs). This method has proved very powerful for analysing the structure of the thin (López-Corredoira et al 2002 and thick ) discs of the Milky Way, as well as in the study of the distribution of interstellar extinction (Drimmel et al 2003;Picaud et al 2003;Duran & van Kerkwijk 2006). The absolute magnitude (M K ) and intrinsic colour, (J − K s ) 0 , of the red-clump giants are well established (Alves 2000;Grocholski & Sarajedini 2002;Salaris & Girardi 2002;Pietrzyński et al 2003).…”

A three-dimensional Galactic extinction model

“…This method has been used for near-plane regions in both the outer and inner Galactic disc (L02; Lopez-Corredoira et al 2003, in preparation) with very satisfactory results. Some estimations of interstellar extinction have also been obtained in this way for the star count predictions of the Besançon model (Robin & Creze 1986) in the Galactic Plane and the results shown there are in good agreement between the observed extinction in the K-band and the model predictions (Picaud et al 2003). The main strength of the method is that it is empirical and we can extract the red-clump giants from the CMDs assuming only their mean absolute magnitude and intrinsic color.…”

3D outer bulge structure from near infrared star counts

“…Nakai 1992; Weinberg 1992; Deguchi et al 1998;Sevenster et al 1999;López-Corredoira et al 2001). The reason for this difference is that they deal with two different things: López-Corredoira et al (2001), then Picaud et al (2003), showed the existence of a structure at l = 20…”