Title: Resolved Massive Star Formation at Low-Metallicity Environment

Speaker: Dr. Rosie Chen (MPIfR)

Time: 13:30, Friday, December 30, 2011

Location: Room 620, Physics Building, NTHU

Abstract:

Massive stars drive the evolution of the interstellar medium and hence play an important role in the evolution of their host galaxies, yet their formation remains poorly understood. Recent Spitzer mid-IR surveys reveal a large number of individually resolved massive young stellar objects (YSOs) in the Magellanic system (LMC, SMC, and Magellanic Bridge). This system covers metallicities of 1/3-1/8 Zo and a range of galaxy-galaxy interactions, providing an excellent opportunity to examine environmental effects on massive star formation and to illuminate what occurred in the early universe. We have used Spitzer and complementary near-IR and optical data to study massive YSOs in HII complexes in the LMC and high N(HI) portion of the Magellanic Bridge (Chen et al. 2009, 2010, 2011). We have modeled spectral energy distributions of YSOs and found their masses ranging 4-45 Mo in the LMC, while 4-10 Mo in the Bridge. Furthermore, for the same mass range, YSOs in the Bridge appear less embedded as almost all of them are visible at optical, opposed to only half in the LMC. The smaller extinction is likely due to the Bridge's lower dust content in the molecular clouds or circumstellar envelopes, or both. To assess the environmental effects, we have estimated the instantaneous star formation efficiency (SFE) using complete lists of YSOs in the LMC and Bridge. We found that the LMC has ~3 times higher SFE than the Bridge, but the trend reverses at N(HI) < 10^21 cm^-2. This reverse is likely caused by different formation mechanisms of molecular clouds, such as colliding flows.