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(abridged) NGC6530 is a young cluster with a complex morphology andstar-formation history. We present a statistical study of its global propertiesusing a new large list of candidate members down to masses of 0.2-0.4 Msun andGaia DR2 astrometry. We consider a wider sky region compared to previousstudies, to investigate the whole cluster and its neighborhood. We study thedistribution of extinction and age across the different regions, and obtainconstraints on the star-formation history. Cluster membership is determined onthe basis of X-ray data, H-alpha emission, near-IR and UV excesses from VPHAS+,UKIDSS and other surveys, and Gaia DR2 astrometry; we also use a novel methodfor photometric selection of M-type pre-main-sequence cluster members. The listof candidates includes nearly 3700 stars, of which we estimate ~2700 genuineNGC6530 members. Using Gaia parallaxes, the cluster distance is found to be1325 pc, with errors of 0.5% (statistical) and 8.5% (systematic), in agreementwith previous determinations. The cluster morphology and boundaries areestablished with great confidence, from members selected using differentcriteria. There is no diffuse population of members around the cluster, butthere are minor member subgroups (associated with the stars 7 Sgr (F2II-III)and HD 164536 (O7.5V)) in addition to the two main groups in the cluster coreand in the Hourglass nebula. We find a pattern of sequential star formation,between ages of <0.5 Myr and ~5 Myr. Extinction is spatially non-uniform, withpart of the population still obscured by thick dust. The precise Gaia propermotion data indicate that the NGC6530 parent cloud collided with the Galacticplane ~4 Myr ago, and we suggest that event as the trigger of the bulk of starformation in NGC6530. The internal cluster dynamics is also partially resolvedby the Gaia data, indicating expansion of the main cluster population.

A wide-area photometric and astrometric (Gaia DR2) study of the young cluster NGC 6530