Spitzer View of Young Massive Stars in the LMC HII Complexes. II. N159

TL;DR

This study investigates the star formation activity in the N159 HII complex of the LMC, identifying YSOs and analyzing their properties to understand the influence of environment and feedback on massive star formation.

Contribution

It provides a detailed analysis of YSO populations in N159's GMCs, revealing differences in star formation stages and feedback effects, and compares various star formation rate indicators.

Findings

Massive YSOs are found in N159B, N159-E, and N159-W, but not in N159-S.

Star formation in N159-W appears spontaneous, while N159-E may have triggered collapse.

Star formation rates from YSO counts align with those from H-alpha and 24 micron luminosities.

Abstract

The HII complex N159 in the Large Magellanic Cloud (LMC) is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their SEDs to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N159B, a maser source, and several ultracompact HII regions. Massive O-type YSOs are found in GMCs N159-E and N159-W, which are associated with ionized gas, i.e., where massive stars formed a few Myr ago. The third GMC, N159-S, has neither O-type YSOs nor evidence of previous massive star formation. This correlation between current and antecedent formation of massive stars suggests that energy feedback is relevant. We present evidence that N159-W is forming YSOs spontaneously, while collapse in N159-E may be triggered. Finally, we compare star formation rates determined from YSO counts with those from integrated H-alpha and 24 micron luminosities and expected from gas surface densities. Detailed dissection of extragalactic GMCs like the one presented here is key to revealing the physics underlying commonly used star formation scaling laws.