The Lagoon Nebula and its vicinity

The Lagoon Nebula is an HII region in the Sagittarius Arm, about 1.3 kpc away, associated with the young (1-3 Myr) open cluster NGC6530, which contains several O stars and several dozen B stars. Lower-mass cluster members, detected by X-ray and Hα emission, and by near-IR excess, number more than a thousand. Myr-old star formation is traced by the optically-visible HII region and cluster; observations of infrared and submillimetre-wave emission, and of optical emission features, indicate ongoing star formation in several locations across the Lagoon. The most prominent of these are the Hourglass Nebula and M8 E. Submillimetre-wave observations also reveal many clumps of dense molecular gas, which may form the next generation of stars. The complex structure of the region has been shaped by the interaction of the underlying molecular gas with multiple massive stars and episodes of star formation. NGC6530 is the oldest component, with the newest stars found embedded in the molecular gas behind the cluster and at its southern rim. A degree to the east of the Lagoon, Simeis 188 is a complex of emission and reflection nebulae, including the bright-rimmed cloud NGC6559; the presence of Hα emission stars suggests ongoing star formation.