The large Lower Centaurus-Crux moving group as seen by Gaia DR2

Scorpius-Centaurus is the nearest OB association and its hundreds of members have been divided into several large sub-groups, including Lower Centaurus-Crux. Here we investigate the stellar and substellar content of the Lower Centaurus Crux area using the Gaia DR2 astrometric and photometric measurements. We report the discovery of more than 1800 intermediate- and low-mass young stellar objects and brown dwarfs located in this area, that had escaped identification until Gaia DR2 provided accurate astrometry and photometry to perform a kinematic and photometric selection. The median distance of this region is 114.5 pc and 80% of the stars lie between 102 and 135 pc from the Sun. Our new members cover a mass range of 5 M$_\odot$ to 0.02 M$_\odot$, with a completeness of 50% at the low-mass end, and add up to a total mass of about 700 M$_\odot$. The present-day mass function follows a log-normal law with m$_c$ = 0.22 M$_\odot$ and $\sigma$ = 0.64, and we find more than 200 brown dwarfs in our sample. The star formation rate had its maximum of $8\times10^{-5}\rm M_\odot yr^{-1}$ at about 9 Myr ago, We grouped the new members in four denser subgroups, which have increasing age from 7 to 10 Myr, surrounded by "free-floating" young stars with mixed ages. The whole complex is presently expanding, and the expansion started between 8 to 10 Myr ago. Two hundred members show infrared excess compatible with circumstellar disks in various stages of evolution from full to debris disks. This discovery provides a large sample of nearby young stellar and sub-stellar objects for disk and exoplanet studies.