Near-Infrared Study of M16: Star Formation in the Elephant Trunks

We present combined J, H, and Ks images of M16 that were obtained with SIRIUS (Simultaneous three-color InfraRed Imager for Unbiased Surveys) on the University of Hawaii 2.2 m telescope. In contrast to optical images, the infrared images show that the Eagle Nebula's "pillars" have head-tail structures, with the heads faced toward the central part of the star cluster NGC 6611 and the tails trailed toward the opposite side. We have found a number of previously unreported young stellar object (YSO) candidates associated with these head-tail pillars. In particular, the youngest YSOs are located at the tips of the pillars or globules, facing toward the central part of NGC 6611. Some are associated with near-infrared jets or cometary reflection nebulae, with indications of a circumstellar disk. This YSO distribution and the cloud structures suggest that the most recent star formation is taking place following the interaction with UV light from the OB stars in NGC 6611.