Author(s): , , , , , , , , , , , ,
Institution(s): 1. Max Planck Institute for Astronomy, 2. Nagoya University, 3. National Astronomical Observatory of Japan, 4. Oska Prefecture University, 5. Space Science Institute, 6. Space Telescope Science Institute, 7. The Johns Hopkins University, 8. University of Illinois, 9. University of Toulouse, 10. University of Virginia
High-mass stars usually form in giant molecular clouds (GMCs) as part of a young stellar cluster, but some isolated O/B stars are observed. What are the initial conditions that lead to the formation of these objects? The aim of this study is to measure the distribution and basic physical properties of the neutral gas associated with isolated intermediate- and high-mass young stellar objects (YSOs) in the Large Magellanic Cloud.
As part of the SAGE Spitzer Legacy program for the LMC, we have identified and confirmed the YSOs using Spitzer IRAC photometry and IRS spectroscopy. By examining the spatial coincidence between the YSOs and 12CO(1-0) emission detected by the NANTEN mapping survey, we identified more than one hundred intermediate/massive YSOs in the LMC that appear to be isolated, i.e. not associated with CO emission. Deeper follow-up CO observations by our team with the higher resolution Mopra Telescope (beam=30") detected CO emission at the YSO position for ~80% of the isolated LMC YSOs. The CO emission associated with the YSOs was sometimes spatially extended, but in some cases, the CO emission was only detected exactly coincident with the YSO position. The molecular clouds associated with these YSOs must therefore have sizes smaller than 8 pc and masses less than a few thousand solar masses.
We obtained ALMA observations of some of the targets during Cycle 2. We targeted a small but representative (in terms of their association with neutral gas tracers) sample of the isolated high-mass YSOs that we have been studying in the LMC. All of our 14 targets are separated by more than 200pc from known CO clouds or the edges of HI supershells to exclude potential "runaway" sources. Our preliminary analysis of the ALMA data shows that a compact 13CO(1-0) cloud whose mass is a few thousand solar masses or smaller is associated with most of the YSOs.