Near-infrared imaging observations of the N159/N160 complex in the large magellanic cloud: Large clusters of Herbig Ae/Be stars and sequential cluster formation

We have carried out deep near-infrared imaging observations of the N159/N160 star-forming region in the Large Magellanic Cloud. We observed an area of ∼380 arcmin ² (∼80,000 pc ² at the distance of the LMC) in the J, H, and K _s bands. The observations are deep enough to detect Herbig Ae/Be stars down to ∼3 M _⊙ in the LMC. We discovered a total of 338 and 464 candidate Herbig Ae/Be and OB stars, respectively, based on the near-infrared colors and magnitudes. The Herbig Ae/Be candidates comprise 10 clusters, the OB star candidates 13. We discovered an embedded Herbig Ae/Be cluster in the N159 East giant molecular cloud (GMC) and a Herbig Ae/Be cluster at the northeast tip of the N159 South GMC. Together with two neighboring H II regions, the Herbig Ae/Be cluster at the tip of the N159S GMC provides a hint of the beginning of sequential cluster formation in N159S. The spatial distributions of the Herbig Ae/Be and OB clusters, in conjunction with previously known optical clusters and embedded massive stars, indicate (1) sequential cluster formation within each of the N159 and N160 star-forming regions and (2) large-scale sequential cluster formation over the entire observed region from N160 to N159S. Possible triggers for the large-scale cluster formation are the supergiant shell SGS 19 and an expanding superbubble. Some of the Herbig Ae/Be clusters in the N159/N160 complex are significantly larger in spatial extent than pre-main-sequence clusters of similar age in the Milky Way. Highly turbulent gas motion in the LMC is probably responsible for forming the large young clusters.