Open superclusters I: The most populated primordial groups of open clusters in the third quadrant of the Galactic disc

TL;DR

This study identifies and characterizes 17 open superclusters in the third galactic quadrant using Gaia data, revealing their composition, substructure, and implications for star formation and cluster evolution.

Contribution

It provides the first detailed survey of open superclusters in this region, discovering new members and subgroups, and supports the primordial group hypothesis.

Findings

17 OSCs identified in the third galactic quadrant

Discovery of four new young clusters within OSCs

OSC subgroups indicate multiple star formation episodes

Abstract

An open supercluster (OSC) is defined as a cluster of at least six open clusters (OCs) born from the same giant molecular cloud (GMC). We survey the recent catalogs of OCs based on Gaia data and relevant literature to find 17 OSCs of the third galactic quadrant, along with 190 likely members of them. OSCs are frequent enough to be considered an extra class of objects in the hierarchy of star formation. Some of these supersystems are new and most of them contain more members than previously thought. The detailed study of some OSCs has leaded to the discovery of four new young clusters that are members of them, named Casado-Hendy 2 to 5. In certain instances, subgroups with distinct PMs or 3D positions have been found within an OSC, suggesting the presence of multiple generations of stars formed from several bursts of star formation within the same GMC. OSCs are typically unbound and tend to disintegrate on timescales of 0.1 Gyr. The present results support the Primordial Group hypothesis (Casado 2022) and suggest that globular clusters are not formed from the accretion of open superclusters, at least in the local Universe at late times.