Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS

Abstract

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 − K s ) color of red clump giants in small subfields of 2 × 2 to 6 × 6 in the following bulge area:• . To determine the reddening values E(J − K s ) for each region, we measure the RC color and compare it to the (J − K s ) 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 A Ks 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.

Infrared spectroscopy of asymptotic giant branch stars in the Galactic bulge

“…Therefore, all other naked stars must be subject to more interstellar extinction than NGC 6522-15. Note that this also agrees with the literature values by Schultheis et al (1999) and Gonzalez et al (2012). For each of the remaining naked stars, we then created a set of extinction-corrected spectra, using A K values (the indicating that these may not reflect 'true' A K values) ranging from 0 to 1 mag in steps of 0.01, and we divided each corrected spectrum by the reference spectrum .…”

“…The interstellar PAH emission is clearly patchy and variable even on these scales, and there is also some variation in the literature extinction values (see Table 4). Schultheis et al (1999) find that extinction values for our targets range from A K = 0.48 to 0.60 with a median of A K = 0.51; Gonzalez et al (2012) on the other hand find a range A K = 0.73−0.84 with the median at A K = 0.78. The variations in A K furthermore appear to correspond qualitatively with the intensity of the PAH emission in the images: extinction is lowest (at A K = 0.48 when using the Schultheis values) for c32-13 (left off centre) where little PAH emission is apparent; it is somewhat Figure B1.…”

“…b Sumi (2004). c Gonzalez et al (2012). d This work; determined from the best-fitting slab models and adopting the GC extinction law.…”

“…For our fields, especially the work by Schultheis et al (1999) and Sumi (2004) are relevant. More recently, also Gonzalez et al (2012) produced an extinction map for the Galactic bulge. The corresponding A K values for all three sources are listed in Table 2.…”

Separation of stellar populations by an evolving bar: implications for the bulge of the Milky Way

“…Fig. 20 shows the projected mean distance to red clump stars from Gonzalez et al (2012) compared to that from RR Lyrae. We used the individual distances to the RR Lyrae from Dékány et al (2013) to calculate a mean RR Lyrae distance using a Gaussian fit to the distance distribution in each line of sight.…”