Carina's Defiant Finger: HST Observations of a Photoevaporating Globule in NGC3372

Abstract

We present HST/WFPC2 images of a prominent externally-ionized molecular globule in the Carina Nebula (NGC3372), supplemented with ground-based IR images and visual-wavelength spectra. This molecular globule has a shape resembling a human hand, with an extended finger that points toward its likely source of ionizing radiation. The dominant ionizing source of the globule is either the WNL star WR25 (HD93162), the O4 If-type star Tr16-244, or perhaps both. We estimate a mass-loss rate of ~2e-5 Msun/yr from the main evaporating surface of the globule, suggesting a remaining lifetime of 10^5.3 to 10^6 years. We find a total mass for the entire globule of more than 6 Msun, in agreement with previous estimates. The hydrogen column density through the globule is a few times 10^22/cm2. Although a few reddened stars are seen within the boundary of the globule in near-IR continuum images, these may be background stars. We do not detect a reddened star at the apex of the finger, for example, down to a limiting magnitude of K=17. However, considering the physical properties of the globule and the advancing ionization front, it appears that future star formation is likely in the Finger globule, induced by radiation-driven implosion.