Significance Mode Analysis SigMA for hierarchical structures An application to the Sco-Cen OB association by Sebastian Ratzenböck et al. on Tuesday 29 November

We present a new clustering method, Significance Mode Analysis (SigMA), to

extract co-spatial and co-moving stellar populations from large-scale surveys

such as ESA Gaia. The method studies the topological properties of the density

field in the multidimensional phase space. We validate SigMA on simulated

clusters and find that it outperforms competing methods, especially in cases

where many clusters are closely spaced. We apply the new method to Gaia DR3

data of the closest OB association to Earth, Scorpio-Centaurus (Sco-Cen), and

find more than 13,000 co-moving young objects, with about 19% of these having a

sub-stellar mass. SigMA finds 37 co-moving clusters in Sco-Cen. These clusters

are independently validated by their narrow HRD sequences and, to a certain

extent, by their association with massive stars too bright for Gaia, hence

unknown to SigMA. We compare our results with similar recent work and find that

the SigMA algorithm recovers richer populations, is able to distinguish

clusters with velocity differences down to about 0.5 km s$^{-1}$, and reaches

cluster volume densities as low as 0.01 sources/pc$^3$. The 3D distribution of

these 37 coeval clusters implies a larger extent and volume for the Sco-Cen OB

association than typically assumed in the literature. Additionally, we find the

association to be more actively star-forming and dynamically more complex than

previously thought. We confirm that the star-forming molecular clouds in the

Sco-Cen region, namely, Ophiuchus, L134/L183, Pipe Nebula, Corona Australis,

Lupus, and Chamaeleon, are part of the Sco-Cen The application of SigMA to

Sco-Cen demonstrates that advanced machine learning tools applied to the superb

Gaia data allows to construct an accurate census of the young populations, to

quantify their dynamics, and to reconstruct the recent star formation history

of the local Milky Way.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14225v1