First Phase Space Portrait of a Hierarchical Stellar Structure in the Milky Way

Emanuele Dalessandro*, A. L. Varri, M. Tiongco, E. Vesperini, C. Fanelli, A. Mucciarelli, L. Origlia, M. Bellazzini, S. Saracino, E. Oliva, N. Sanna, M. Fabrizio, A. Livernois

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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° diameter) surrounding the well-known h and χ Persei double stellar cluster in the Perseus Arm. Gaia-EDR3 shows that the area is populated by seven comoving clusters, three of which were previously unknown, and by an extended and quite massive (M ~ 105 M⊙) halo. All stars and clusters define a complex structure with evidence of possible mutual interactions in the form of intra-cluster overdensities and/or bridges. They share the same chemical abundances (half-solar metallicity) and age (t ~ 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 pieces of evidence suggests that stars distributed within a few degrees from h and χ Persei are part of a common, substructured 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 times 105 M⊙) stellar system. We argue that such a 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.
Original languageEnglish
Article number90
Pages (from-to)1-10
Number of pages10
JournalAstrophysical Journal
Volume909
Issue number1
DOIs
Publication statusPublished - 9 Mar 2021

Keywords

  • astro-ph.GA
  • astro-ph.SR

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