A two-dimensional map of the color excess in NGC 3603

Using archival Hubble Space Telescope/Wide Field Camera 3 images centered on the young HD97950 star cluster in the giant H II region NGC3603, we computed the pixel-to-pixel distribution of the color excess, E(B - V)_g, of the gas associated with this cluster from its Hα/Paβ flux ratio. At the assumed distance of 6.9kpc, the resulting median color excess within 1pc from the cluster center is E(B - V)_g = 1.51 ± 0.04mag. Outside the cluster (at r > 1pc), the color excess is seen to increase with cluster-centric distance toward both north and south, reaching a value of about 2.2mag at r = 2pc from the cluster center. The radial dependence of E(B - V)_g westward of the cluster appears rather flat at about 1.55mag over the distance range 1.2pc <r < 3pc. In the eastern direction, E(B - V)_g steadily increases from 1.5mag at r = 1pc to 1.7mag at r = 2pc and stays nearly constant at 1.7mag for 2pc <r < 3pc. The different radial profiles and the pixel-to-pixel variations of E(B - V)_g clearly indicate the presence of significant differential reddening across the 4.9pc × 4.3pc area centered on the HD97950 star cluster. We interpret the variations of E(B - V)_g as the result of stellar radiation and stellar winds interacting with an inhomogeneous dusty local interstellar medium whose density varies spatially. From the E(B - V)_g values measured along the rims of the prominent pillars MM1 and MM2 in the southwest and southeast of the HD97950 cluster, we estimate an H₂ column density of and extrapolate it to in the pillars' interior. We find the pillars to be closer to us than the central ionizing cluster and suggest that star formation may be occurring in the pillar heads.