Cosmic wallflowers: the circumgalactic origins of isolated ultra-compact star clusters at $z>7$

Abstract

The discovery of gravitationally lensed stellar clusters at high redshift with the James Webb Space Telescope (JWST) has revealed extremely compact, massive star-forming systems in galaxies at $z>6$, providing a new window into early cluster formation. In this work, we investigate star cluster formation in the circumgalactic environments of gas-rich galaxies with stellar masses spanning between $\sim$$10^8$ - $10^{11}$ M${}_{\odot }$ at $z>7$, using the MassiveBlackPS cosmological hydrodynamical simulation with 2 pc resolution. We identify 55 baryon-dominated clusters forming outside galactic discs but within the virial radius of the primary halo. Star formation in these systems proceeds rapidly, reaching peak stellar surface densities above $10^5$ M${}_{\odot }$ pc${}^{-2}$, closely matching the compact clusters recently discovered by JWST in the lensed Cosmic Gems Arc at $z\approx 9.6$. Such extreme densities are a key pre-requisite to trigger runaway stellar collisions, indicating that a subset of our clusters would be a likely host of intermediate-mass black holes (IMBHs). We find that massive star clusters can form efficiently in the circumgalactic medium at early times through filament fragmentation, whereby high gas densities lead to rapid local collapse via a combination of thermal and gravitational instabilities. This formation pathway implies that some compact clusters formed in the quiet outskirts of forming galaxies rather than within their discs. Small variations in filament properties, including metallicity, density, and dark-matter content, influence the likelihood of a star cluster being able to form an IMBH seed. The formation of clusters in circumgalactic environments points to a potential evolutionary pathway connecting early off-disc clusters, present-day globular clusters, and the seeds of massive BHs.

14 pages, 11 figures, submitted to MNRAS

References in corpus (53)

• The James Webb Space Telescope
• Formation of Massive Galaxies at High Redshift: Cold Streams, Clumpy Disks and Compact Spheroids
• Star Formation and Feedback in Smoothed Particle Hydrodynamic Simulations--I. Isolated Galaxies
• A CEERS Discovery of an Accreting Supermassive Black Hole 570 Myr after the Big Bang: Identifying a Progenitor of Massive z > 6 Quasars
• JADES. The diverse population of infant Black Holes at 4<z<11: merging, tiny, poor, but mighty
• Formation of the first nuclear clusters and massive black holes at high redshift
• Damped Lyman Alpha Systems in Galaxy Formation Simulations
• STARFORGE: Toward a comprehensive numerical model of star cluster formation and feedback
• A dynamically cold disk galaxy in the early Universe
• A parsec-resolution simulation of the Antennae galaxies: Formation of star clusters during the merger
• Dynamical properties of z $\sim 4.5$ dusty star-forming galaxies and their connection with local early type galaxies
• CEERS Key Paper III: The Diversity of Galaxy Structure and Morphology at z=3-9 with JWST
• Panic! At the Disks: First Rest-frame Optical Observations of Galaxy Structure at $z>3$ with JWST in the SMACS 0723 Field
• Star clusters near and far; tracing star formation across cosmic time
• JWST/NIRCam Probes Young Star Clusters in the Reionization Era Sunrise Arc
• Stochastic modelling of star-formation histories II: star-formation variability from molecular clouds and gas inflow
• Gravitational Wave Recoil and the Retention of Intermediate Mass Black Holes
• Star formation at the smallest scales; A JWST study of the clump populations in SMACS0723
• Intermediate-mass Black Holes from High Massive-star Binary Fractions in Young Star Clusters
• Radii of Young Star Clusters in Nearby Galaxies
• The Sparkler: Evolved High-Redshift Globular Clusters Captured by JWST
• Origins and Demographics of Wandering Black Holes
• Orbital Decay of Supermassive Black Hole Binaries in Clumpy Multiphase Merger Remnants
• Regular rotation and low turbulence in a diverse sample of z ~ 4.5 galaxies observed with ALMA
• Radiation hydrodynamics simulations of massive star cluster formation in giant molecular clouds
• The Origins of Off-Centre Massive Black Holes in Dwarf Galaxies
• Star cluster formation and cloud dispersal by radiative feedback: dependence on metallicity and compactness
• Very Massive Stars and Pair-Instability Supernovae: Mass-loss Framework for low Metallicity
• LISA Definition Study Report
• JADES: Differing assembly histories of galaxies -- Observational evidence for bursty SFHs and (mini-)quenching in the first billion years of the Universe
• Unveiling the Population of Wandering Black Holes via Electromagnetic Signatures
• Simulations predict intermediate-mass black hole formation in globular clusters
• From giant clumps to clouds I: the impact of gas fraction evolution on the stability of galactic discs
• Clumpy high-z galaxies as a testbed for feedback-regulated galaxy formation
• The effect of non-equilibrium metal cooling on the interstellar medium
• Super-critical accretion of medium-weight seed black holes in gaseous proto-galactic nuclei
• Thermal instability and multi-phase interstellar medium in the first galaxies
• Star Cluster Formation and Survival in the First Galaxies
• The dawn of disks: unveiling the turbulent ionised gas kinematics of the galaxy population at $z\sim 4-6$ with JWST/NIRCam grism spectroscopy
• The mass budget for intermediate-mass black holes in dense star clusters
• Detectability of Wandering Intermediate-Mass Black Holes in the Milky Way Galaxy from Radio to X-rays
• Growth of Massive Black-Holes in FFB Galaxies at Cosmic Dawn
• Gas clump formation via thermal instability in high-redshift dwarf galaxy mergers
• Stellar cluster formation in a Milky Way-sized galaxy at z>4 -- I. The proto-globular cluster population and the imposter amongst us
• New constraints on the central mass contents of Omega Centauri from combined stellar kinematics and pulsar timing
• A panchromatic view of star cluster formation in a simulated dwarf galaxy starburst
• Formation of free-floating planetary mass objects via circumstellar disk encounters
• The Fraction of Clumpy Galaxies in JADES Over $2<z<9$
• On the origin of compressive turbulence in protoclumps in high redshift disks
• Seeding Cores: A Pathway for Nuclear Star Clusters from Bound Star Clusters in the First Billion Years
• The dynamical evolution of the stellar clumps in the Sparkler galaxy
• Signatures of star formation inside galactic outflows
• The Seven Dwarfs illuminated. The impact of radiation on dwarf galaxies and their circumgalactic medium

Cited by in corpus (1)

• FROST-CLUSTERS -- III. Metallicity-dependent intermediate mass black hole formation by runaway collisions in dense star clusters