Illuminating the Tadpole's metamorphosis I: MUSE observations of a small globule in a sea of ionizing photons

TL;DR

This study uses MUSE/VLT observations to analyze a small globule in the Carina H II region, revealing its physical properties, ionization structure, and potential role in star formation and the initial mass function.

Contribution

First detailed spatially-resolved analysis of a globule in Carina, challenging previous mass estimates and implications for star formation in small globules.

Findings

Globule has high temperature (~10^4 K) and modest density (~200 cm$^{-3}$).

Bonnor-Ebert mass of ~3.7 M$_{ ext{odot}}$ suggests larger mass than previously thought.

Globule will be photoevaporated in about 7 million years.

Abstract

We present new MUSE/VLT observations of a small globule in the Carina H II region that hosts the HH 900 jet+outflow system. Data were obtained with the GALACSI ground-layer adaptive optics system in wide-field mode, providing spatially-resolved maps of diagnostic emission lines. These allow us to measure the variation of the physical properties in the globule and jet+outflow system. We find high temperatures ($T_e \approx 10^4$ K), modest extinction ($A_V \approx 2.5$ mag), and modest electron densities ($n_e \approx 200$ cm$^{-3}$) in the ionized gas. Higher excitation lines trace the ionized outflow; both the excitation and ionization in the outflow increase with distance from the opaque globule. In contrast, lower excitation lines that are collisionally de-excited at densities $\gtrsim 10^4$ cm$^{-3}$ trace the highly collimated protostellar jet. Assuming the globule is an isothermal sphere confined by the pressure of the ionization front, we compute a Bonnor-Ebert mass of $\sim 3.7$ M$_{\odot}$. This is two orders of magnitude higher than previous mass estimates, calling into question whether small globules like the Tadpole contribute to the bottom of the IMF. Derived globule properties are consistent with a cloud that has been and/or will be compressed by the ionization front on its surface. At the estimated globule photoevaporation rate of $\sim 5 \times 10^{-7}$ M$_{\odot}$ yr$^{-1}$, the globule will be completely ablated in $\sim 7$ Myr. Stars that form in globules like the Tadpole will emerge into the H II later and may help resolve some of the temporal tension between disk survival and enrichment.