Formation of proto-globular cluster candidates in cosmological simulations of dwarf galaxies at z > 4.

We perform cosmological hydrodynamical simulations to study the formation of proto-globular cluster candidates in progenitors of present-day dwarf galaxies |$(M_{\rm vir} \approx 10^{10}\, {\rm M}_\odot$| at z = 0) as part of the 'Feedback in Realistic Environment' (FIRE) project. Compact (r _1/2 < 30 pc), relatively massive (0.5 × 10⁵ ≲ M _⋆/M_⊙ ≲ 5 × 10⁵), self-bound stellar clusters form at 11 ≳ z ≳ 5 in progenitors with |$M_{\rm vir} \approx 10^9\, \mathrm{M}_{\odot }$|⁠. Cluster formation is triggered when at least |$10^7\, \mathrm{M}_{\odot }$| of dense, turbulent gas reaches |$\Sigma _{\rm gas} \approx 10^4\, {\rm M}_\odot \, {\rm pc}^{-2}$| as a result of the compressive effects of supernova feedback or from cloud–cloud collisions. The clusters can survive for |$2-3\, {\rm Gyr}$|⁠ ; absent numerical effects, they could possibly survive substantially longer, perhaps to z = 0. The longest lived clusters are those that form at significant distance – several hundreds of pc – from their host galaxy. We therefore predict that globular clusters forming in progenitors of present-day dwarf galaxies will be offset from any pre-existing stars within their host dark matter haloes as opposed to deeply embedded within a well-defined galaxy. Properties of the nascent clusters are consistent with observations of some of the faintest and most compact high-redshift sources in Hubble Space Telescope lensing fields and are at the edge of what will be detectable as point sources in deep imaging of non-lensed fields with JWST. By contrast, the star clusters' host galaxies will remain undetectable. [ABSTRACT FROM AUTHOR]