Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS⋆
II. The complete high resolution extinction map and implications for Galactic bulge studies
O. A. Gonzalez1, M. Rejkuba1, M. Zoccali2,3, E. Valenti1, D. Minniti2,4, M. Schultheis5, R. Tobar1 and B. Chen5
1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
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2 Departamento Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
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3 INAF – Osservatorio Astronomico di Bologna, via Ranzani, 40127 Bologna, Italy
4 Vatican Observatory, V00120 Vatican City State, Italy
5 Institut Utinam, CNRS UMR6213, OSU THETA, Université de Franche-Comté, 41bis avenue de l’Observatoire, 25000 Besançon, France
Received: 14 March 2012
Accepted: 15 April 2012
Context. The Milky Way bulge is the nearest galactic bulge and the most readily accessible laboratory for studies of stellar populations in spheroids based on individual stellar abundances and kinematics. These studies are challenged by the strongly variable and often large extinction on a small spatial scale.
Aims. We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution.
Methods. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J − Ks) color of red clump giants in small subfields of 2′ × 2′ to 6′ × 6′ in the following bulge area: − 10.3° ≤ b ≤ + 5.1° and − 10.0° ≤ l ≤ + 10.4°. To determine the reddening values E(J − Ks) for each region, we measure the RC color and compare it to the (J − Ks) color of RC stars measured in Baade’s Window, for which we adopt E(B − V) = 0.55. This allows us to construct a reddening map sensitive to small-scale variations minimizing the problems arising from differential extinction.
Results. The significant reddening variations are clearly observed on spatial scales as small as 2′. We find good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are unreliable for regions within |b| ≲ 6°. In the inner regions, we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map is of higher quality owing to both its higher resolution and a more complete spatial coverage of the bulge. We investigate the importance of differential reddening and demonstrate the need for high spatial resolution extinction maps for detailed studies of bulge stellar populations and structure.
Conclusions. We present the first extinction map covering uniformly ~315 sq. deg. of the Milky Way bulge at high spatial resolution. We consider a 30 arcmin window at a latitude of b = −4°, which corresponds to a frequently studied low extinction window, the so-called Baade’s Window, and find that its AKs values can vary by up to 0.1 mag. Larger extinction variations are observed at lower Galactic latitudes. The extinction variations on scales of up to 2′−6′ must be taken into account when analyzing the stellar populations of the Galactic bulge.
Key words: Galaxy: bulge / dust, extinction / stars: abundances
© ESO, 2012