First phase space portrait of a hierarchical stellar structure in the Milky Way

Abstract

We present the first detailed observational picture of a possible ongoing massive cluster hierarchical assembly in the Galactic disk as revealed by the analysis of the stellar full phase-space (3D positions and kinematics and spectro-photometric properties) of an extended area ($6^{\circ }$ diameter) surrounding the well-known $h$ and $\chi$ Persei double stellar cluster in the Perseus Arm. Gaia-EDR3 shows that the area is populated by seven co-moving clusters, three of which were previously unknown, and by an extended and quite massive ($M\sim 10^5{M}_{\odot }$) halo. All stars and clusters define a complex structure with evidence of possible mutual interactions in the form of intra-cluster over-densities and/or bridges. They share the same chemical abundances (half-solar metallicity) and age ($t\sim 20$ Myr) within a small confidence interval and the stellar density distribution of the surrounding diffuse stellar halo resembles that of a cluster-like stellar system. The combination of these evidences suggests that stars distributed within a few degrees from $h$ and $\chi$ Persei are part of a common, sub-structured stellar complex that we named LISCA I. Comparison with results obtained through direct $N$-body simulations suggest that LISCA I may be at an intermediate stage of an ongoing cluster assembly that can eventually evolve in a relatively massive (a few $10^5{M}_{\odot }$) stellar system. We argue that such cluster formation mechanism may be quite efficient in the Milky Way and disk-like galaxies and, as a consequence, it has a relevant impact on our understanding of cluster formation efficiency as a function of the environment and redshift.

19 pages, 8 figures, 1 table; accepted for publication in ApJ

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Cited by in corpus (10)

• Binary open clusters in the Gaia data
• Investigating Galactic binary cluster candidates with Gaia EDR3
• Ongoing hierarchical massive cluster assembly: the LISCA II structure in the Perseus complex
• Enlightening the dynamical evolution of Galactic open clusters: an approach using Gaia DR3 and analytical descriptions
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• The Formation of Binary Star Clusters in the Milky Way and Large Magellanic Cloud
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