A Two-dimensional Map of Color Excess in NGC 3603
  Using archival HST/WFC3 images centered on the young HD 97950 star cluster in
the giant HII region NGC 3603, we computed the pixel-to-pixel distribution of
the color excess, E(B-V)g, of the gas associated with this cluster from its
H_alpha/Pa_beta flux ratio. At the assumed distance of 6.9 kpc, the resulting
median color excess within 1 pc from the cluster center is E(B-V)g =1.51 \pm
0.04 mag. Outside the cluster (at r > 1 pc), the color excess is seen to
increase with cluster-centric distance towards both North and South, reaching a
value of about 2.2 mag at r = 2 pc from the cluster center. The radial
dependence of E(B-V)g westward of the cluster appears rather flat at about 1.55
mag over the distance range 1.2 pc < r < 3 pc. In the eastern direction,
E(B-V)g steadily increases from 1.5 mag at r = 1 pc to 1.7 mag at r = 2 pc, and
stays nearly constant at 1.7 mag for 2 pc < r < 3 pc. 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 4.9 pc \times 4.3 pc
area centered on the HD 97950 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 (ISM) 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 HD 97950 cluster we
estimate an H2 column density of log10(N(H2))=21.7 and extrapolate it to
log10(N(H2))=23 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.
