| Description |
Stars form from contracting molecular cores, but this process relies heavily on the ability of the core to cool. This depends on chemical composition and could therefore lead to different outcomes at low metallicity. However, most of what we know about star formation is derived from studies of Galactic YSOs. Herschel provides the unmissableopportunity to extend such analysis to the low-metallicity environments of the Large and Small Magellanic Clouds (LMC and SMC), by observing the main cooling lines: fine-structure lines of oxygen and carbon, and rotational transitions of abundant molecules.Our Spitzer Legacy Programs (SAGE; SAGE-SMC) and Herschel Key Program (HERITAGE)identified 1000s of young stellar objects (YSOs), in both Clouds. Follow-up spectroscopy(Spitzer-IRS and ESO/VLT) provided unique insight into the abundances of ices in Magellanic YSOs, revealing differences in the composition of circumstellar material at lower metallicity. Since the gas and ice phase chemistry is inextricably linked, this opensthe possibility of significant variations to gas-phase abundances. Such differences could imply changes to cooling and heating rates, and consequently different star formation timescales and efficiencies.To investigate the role of metallicity we will observe a sample of embedded massive Magellanic YSOs. We will use PACS and SPIRE FTS spectrographs to measure the strengths of key gas-phase cooling species (OI, OIII, CII, H2O, CO, OH), in order to estimate temperature, density, ionization state and abundances. These observations will enable us to characterise the gas and constrain the cooling budget of the YSO envelopes. Together with our ice column density measurements, the Herschel observations are crucial to investigate how grain-surface reactions change the chemical make-up of the gas. By comparing the SMC and LMC, and Galactic YSO samples we will assess how the chemistry, and consequently the ability of the YSO envelopes to cool, differ at sub-solar metallicity. |
