Low-extinction windows in the inner Galactic Bulge

Abstract

We built K band extinction maps in the area of two candidate low-extinction windows in the inner Bulge: W0.2-2.1 at (l,b) = (0.25o,-2.15o), and W359.4-3.1 at (l,b) = (359.40o,-3.10o). We employed JHKs photometry from the 2MASS Point Source Catalog. Extinction values were determined by fitting the upper giant branch found in the present 2MASS Ks x J-Ks diagrams to a de-reddened bulge stellar population reference giant branch. We tested the method on the well known Baade's and Sgr I windows: the 2MASS mean extinction values in these fields agreed well with those of previous studies. We confirm the existence of low-extinction windows in the regions studied, as local minima in the A_K maps reaching A_K values about 2 standard deviations below the mean values found in the neighbouring areas. Schlegel et al.'s (1998) FIR extinction maps, which integrate dust contributions throughout the Galaxy, are structurally similar to those derived with 2MASS photometry in the two studied windows. We thus conclude that the dust clouds affecting the 2MASS and FIR maps in these directions are basically the same and are located on foreground of the bulk of bulge stars. However, the A_K absolute values differ significantly. In particular, the FIR extinction values for W359.4-3.1 are a factor ~1.45 larger than those derived from the 2MASS photometry. Possible explanations of this effect are discussed. The lower Galactic latitudes of the low-extinction windows W359.4-3.1 and W0.2-2.1, as compared to Baade's Window, make them promising targets for detailed studies of more central bulge regions.Comment: 8 pages, 10 figures, LaTeX, aa.cls. To appear in Astron. & Astroph., in pres