Mapping the Milky Way bulge at high resolution: the 3D dust extinction, CO, and X factor maps

Abstract

Context. Three dimensional interstellar extinction maps provide a powerful tool for stellar population analysis. However, until now, these 3D maps were rather limited by sensitivity and spatial resolution. Aims. We use data from the VISTA Variables in the Via Lactea survey together with the Besançon stellar population synthesis model of the Galaxy to determine interstellar extinction as a function of distance in the Galactic bulge covering −10 • < l < 10 • and −10 • < b < 5 • . Methods. We adopted a recently developed method to calculate the colour excess. First we constructed the H − Ks vs. Ks and J − Ks vs. Ks colour−magnitude diagrams based on the VVV catalogues that matched 2MASS. Then, based on the temperature−colour relation for M giants and the distance-colour relations, we derived the extinction as a function of distance. The observed colours were shifted to match the intrinsic colours in the Besançon model as a function of distance iteratively. This created an extinction map with three dimensions: two spatial and one distance dimension along each line of sight towards the bulge. Results. We present a 3D extinction map that covers the whole VVV area with a resolution of 6 × 6 for J − Ks and H − Ks using distance bins of 0.5 kpc. The high resolution and depth of the photometry allows us to derive extinction maps for a range of distances up to 10 kpc and up to 30 mag of extinction in A V (3.0 mag in A Ks ). Integrated maps show the same dust features and consistent values as other 2D maps. We discuss the spatial distribution of dust features in the line of sight, which suggests that there is much material in front of the Galactic bar, specifically between 5−7 kpc. We compare our dust extinction map with the high-resolution 12 CO maps (NANTEN2) towards the Galactic bulge, where we find a good correlation between 12 CO and A V . We determine the X factor by combining the CO map and our dust extinction map. Our derived average value X = 2.5 ± 0.47 × 10 20 cm −2 K −1 km −1 s is consistent with the canonical value of the Milky Way. The X-factor decreases with increasing extinction.

H i, CO, and Dust in the Perseus Cloud

“…This anti-correlation reflects that in the diffuse (low-W CO ) region CO molecule is photo-dissociated more effectively than H 2 , and therefore X CO increases. This trend is consistent with the result in Cotten & Magnani (2013); Schultheis et al (2014), and we can say that the spatial distribution of X CO can be well calculated by using the present method.…”

Milky Way demographics with the VVV survey

“…This is supported by the 3D dust extinction maps by Schultheis et al (2014), who found a large jump in extinction at low latitude located at a distance of about 6 kpc along the line of sight to the bulge. This may be the signature of a dust ring as seen in other galaxies that have suffered recent mergers (such as M 64 or NGC 5128).…”

A Detailed Observational Analysis of V1324 Sco, the Most Gamma-Ray-luminous Classical Nova to Date

“…We estimate -= ( ) E B V  1.16 0.12. Three-dimensional reddening maps of the Galaxy (Schultheis et al 2014) imply that V1324Sco is >6.5 kpc away (see also Munari et al 2015 for similar results). V1324Sco's location near or beyond the Galactic bulge implies that it is significantly more gamma-ray luminous than other gamma-ray-detected novae ( ǵ L 2 10 36 erg s −1 in the energy range 100 MeV-10 GeV, exceeding other novae by order of magnitude; Ackermann et al 2014;Finzell et al 2015).…”