Hunting for open clusters in Gaia EDR3: 628 new open clusters found with OCfinder

Context. The improvements in the precision of the published data in Gaia EDR3 with respect to Gaia DR2, particularly for parallaxes and proper motions, offer the opportunity to increase the number of known open clusters in the Milky Way by detecting farther and fainter objects that have thus far gone unnoticed. Aims. Our aim is to continue to complete the open cluster census in the Milky Way with the detection of new stellar groups in the Galactic disc. We use Gaia EDR3 up to magnitude G = 18 mag, increasing the magnitude limit and therefore the search volume explored in one unit with respect to our previous studies. Methods. We used the OCfinder method to search for new open clusters in Gaia EDR3 using a big data environment. As a first step, OCfinder identified stellar statistical overdensities in five-dimensional astrometric space (position, parallax, and proper motions) using the DBSCAN clustering algorithm. Then, these overdensities were classified into random statistical overdensities or real physical open clusters using a deep artificial neural network trained on well-characterised G, G(BP) - G(RP) colour-magnitude diagrams. Results. We report the discovery of 628 new open clusters within the Galactic disc, with most of them being located beyond 1 kpc from the Sun. From the estimation of ages, distances, and line-of-sight extinctions of these open clusters, we see that young clusters align following the Galactic spiral arms while older ones are dispersed in the Galactic disc. Furthermore, we find that most open clusters are located at low Galactic altitudes with the exception of a few groups older than 1 Gyr. Conclusions. We show the success of the OCfinder method leading to the discovery of a total of 1274 open clusters (joining the discoveries here with the previous ones based on Gaia DR2), which represents almost 50% of the known population. Our ability to perform big data searches on a large volume of the Galactic disc, together with the higher precision in Gaia EDR3, enable us to keep completing the census with the discovery of new open clusters.

Automated summary

This study used Gaia EDR3 data and the OCfinder method to discover 628 new open clusters in the Galactic disc, with most of them located beyond 1 kpc from the Sun. Young clusters align along the Galactic spiral arms, while older clusters are dispersed in the disc, and most open clusters are located at low Galactic altitudes.