We propose that cold filamentary accretion in massive galaxies at high redshifts can lead to the formation of starforming clumps in the halos of these galaxies without dark matter substructure. In certain cases, these clumps can be the birthplaces of metal-poor globular clusters (MP GCs). Using cosmological simulations, we show that narrow streams of dense gas feeding massive galaxies from the cosmic web can fragment, producing star-forming clumps. We then derive an analytical model for the properties of streams as a function of halo mass and redshift, and assess when these are gravitationally unstable, when this can lead to collapse and star formation in the halo, and when it may result in the formation of MP GCs. For stream metallicities ≳0.01Z⊙, this is likely to occur at z ≥ 4.5. At z ∼ 6, the collapsing clouds have masses of ∼(5'10) 107 M⊙, and the average stream pressure is ∼106 cm-3 K. The conditions for GC formation are met in the extremely turbulent "eyewall" at ∼0.3Rv, where counter-rotating streams can collide, driving very large densities. Our scenario can account for the observed kinematics and spatial distribution of MP GCs, the correlation between their mass and metallicity, and the mass ratio between the GC system and the host halo. For MW-mass halos, we infer that ∼30% of MP GCs could have formed in this way, with the remainder likely accreted in mergers. Our predictions for GC formation along circumgalactic filaments at high redshift are testable with JWST.
Bibliographical noteFunding Information:
We thank the anonymous referee for constructive comments, which have improved the quality of this manuscript. We are greatly indebted to Avishai Dekel for inspiring large parts of this work and for his continuous support. We thank Avishai Dekel and Joel Primack for the use of the VELA simulations. We gratefully acknowledge Avishai Dekel, Diederik Kruijssen, and Daisuke Nagai for their careful reading of and thoughtful comments on an earlier version of the mauscript. We thank Yuval Birnboim, Frederic Bournaud, Andi Burkert, Bruce Elmegreen, Kohei Inayoshi, Thorsten Naab, and Stefanie Walch for very helpful discussions. We thank Andrew P. Hearin for his help with the Colossus package used in creating Figure 1. N.M. and F.B. acknowledge support from the Klaus Tschira Foundation through the HITS-Yale Program in Astrophysics (HYPA). F.B. is supported by the US National Science Foundation through grant AST-1516962. J.B. acknowledges support from NSF grant AST-1616598. D.C. has been funded by the ERC Advanced grant STARLIGHT: Formation of the First Stars (project number 339177). The VELA simulations were performed at the National Energy Research Scientific Computing Center (NERSC), Lawrence Berkeley National Laboratory, and at NASA Advanced Supercomputing (NAS) at NASA Ames Research Center (PI: Joel Primack).
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- galaxies: formation
- globular clusters: general