HST/WFPC2 and VLT/ISAAC observations of proplyds in the giant HII region NGC 3603

We report the discovery of three proplyd-like structures in the giant H II region NGC 3603. The emission nebulae are clearly resolved in narrowband an d broadband HST/WFPC2 observations in the optical and broadband VLT/ISAAC o bservations in the near-infrared. All three nebulae are tadpole shaped, wit h the bright ionization front at the head facing the central cluster and a fainter ionization front around the tail pointing away from the cluster. Ty pical sizes are 6000 AU x 20,000 AU The nebulae share the overall morpholog y of the proplyds (PROto PLanetarY DiskS) in Orion, but are 20 to 30 times larger in size. Additional faint filaments located between the nebulae and the central ionizing cluster can be interpreted as bow shocks resulting fro m the interaction of the fast winds from the high-mass stars in the cluster with the evaporation flow from the proplyds. Low-resolution spectra of the brightest nebula, which is at a projected separation of 1.3 pc from the cl uster, reveal that it has the spectral excitation characteristics of an ult ra compact H II region with electron densities well in excess of 10(4) cm(- 3). The near-infrared data reveal a point source superposed on the ionizati on front. The striking similarity of the tadpole-shaped emission nebulae in NGC 3603 to the proplyds in Orion suggests that the physical structure of both types of objects might be the same. We present two-dimensional radiati on hydrodynamical simulations of an externally illuminated star-disk-envelo pe system, which was still in its main accretion phase when first exposed t o ionizing radiation from the central cluster. The simulations reproduce th e overall morphology of the proplyds in NGC 3603 very well, but also indica te that mass-loss rates of up to 10(-5) M . yr(-1) are required in order to explain the size of the proplyds. Due to these high mass-loss rates, the proplyds in NGC 3603 should only sur vive approximate to 10(5) yr. Despite this short survival time, we detect t hree proplyds. This indicates that circumstellar disks must be common aroun d young stars in NGC 3603 and that these particular proplyds have only rece ntly been exposed to their present harsh UV environment.