Ice chemistry in massive Young Stellar Objects: the role of metallicity

TL;DR

This study compares ice compositions in massive Young Stellar Objects across different metallicity environments, revealing how metallicity influences ice chemistry and the physical conditions of star-forming regions.

Contribution

It provides the first comparative analysis of water, CO, and CO2 ices in YSOs within the SMC, LMC, and Galaxy, highlighting metallicity's impact on ice abundances and environmental conditions.

Findings

CO and CO2 ices are enhanced in the LMC compared to the Galaxy.

CO ice is not detected in SMC YSOs.

Lower water column density in the LMC affects ice abundances.

Abstract

We present the comparison of the three most important ice constituents (water, CO and CO2) in the envelopes of massive Young Stellar Objects (YSOs), in environments of different metallicities: the Galaxy, the Large Magellanic Cloud (LMC) and, for the first time, the Small Magellanic Cloud (SMC). We present observations of water, CO and CO2 ice in 4 SMC and 3 LMC YSOs (obtained with Spitzer-IRS and VLT/ISAAC). While water and CO2 ice are detected in all Magellanic YSOs, CO ice is not detected in the SMC objects. Both CO and CO2 ice abundances are enhanced in the LMC when compared to high-luminosity Galactic YSOs. Based on the fact that both species appear to be enhanced in a consistent way, this effect is unlikely to be the result of enhanced CO2 production in hotter YSO envelopes as previously thought. Instead we propose that this results from a reduced water column density in the envelopes of LMC YSOs, a direct consequence of both the stronger UV radiation field and the reduced dust-to-gas ratio at lower metallicity. In the SMC the environmental conditions are harsher, and we observe a reduction in CO2 column density. Furthermore, the low gas-phase CO density and higher dust temperature in YSO envelopes in the SMC seem to inhibit CO freeze-out. The scenario we propose can be tested with further observations.