HST and VLT observations of PROPLYDS in the giant HII region NGC 3603

Wolfgang Brandner, Eva K. Grebel, You-Hua Chu, Horacio Dottori, Bernhard Brandl, Sabine Richling, Harold W. Yorke, Sean D. Points, and Hans Zinnecker

2000 AJ 119, 292


We report the discovery of three proplyd-like structures in the giant HII region NGC 3603. The emission nebulae are clearly resolved in narrow-band and broad-band HST/WFPC2 observations in the optical and broad-band VLT/ISAAC observations in the near-infrared. All three nebulae are tadpole shaped, with the bright ionization front at the head facing the central cluster and a fainter ionization front around the tail pointing away from the cluster. Typical sizes are 6,000 A.U. times 20,000 A.U. The nebulae share the overall morphology 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 from 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 cluster, reveal that it has the spectral excitation characteristics of an Ultra Compact HII region with electron densities well in excess of 10E4/cm^3. The near-infrared data reveal a point-source superimposed on the ionization 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 2D radiation hydrodynamical simulations of an externally illuminated star-disk-envelope system, which was still in its main accretion phase when first exposed to ionizing radiation from the central cluster. The simulations reproduce the overall morphology of the proplyds in NGC 3603 very well, but also indicate that mass-loss rates of up to 10E-5 Mo/yr 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 survive approx 10E5 yr. Despite this short survival time, we detect three proplyds. This indicates that circumstellar disks must be common around young stars in NGC 3603 and that these particular proplyds have only recently been exposed to their present harsh UV environment.

A copy of the article is available at AJ and the LANL Preprint Server.
More information on NGC 3603 is available here.