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ABSTRACT In the local Universe, star formation is typically inefficient both globally and when considered as the fraction of gas converted into stars per local free-fall time. An important exception to this inefficiency is regions of high gravitational accelerations g, or equivalently surface densities $$\Sigma = g/(\pi \, G)$$, where stellar feedback is insufficient to overcome the self-gravity of dense gas clouds. In this paper, I explore whether dark matter can play an analogous role in providing the requisite accelerations on the scale of entire galaxies in the early cosmos. The key insight is that characteristic accelerations in dark matter haloes scale as $(1+z)^2$ at fixed halo mass. I show this is sufficient to make dark matter the source of intense accelerations that might induce efficient star formation on galactic scales at cosmic dawn in sufficiently massive haloes. The mass characterizing this regime scales as $$(1+z)^{-6}$$ and corresponds to a relatively constant comoving number density of $$n(>\!M_{\rm {vir}}) \approx 10^{-4}\, {\rm Mpc}^{-3}$$ at $$z \gtrsim 8$$. For somewhat rarer haloes, this model predicts stellar masses of $$M_{\star }\sim 10^{9}\, {\rm M}_{\odot }$$ can form in regions that end up with sizes $$\mathcal {O}(100\, {\rm pc})$$ over $$40\, {\rm Myr}$$ time-scales at $$z\approx 12-14$$; these numbers compare well to measurements for some of the brightest galaxies at that epoch from JWST observations. Dark matter and standard cosmological evolution may therefore be crucial for explaining the surprisingly high levels of star formation in the early Universe revealed by JWST.
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Stress testing ΛCDM with high-redshift galaxy candidates
Abstract Early data from the James Webb Space Telescope (JWST) have revealed a bevy of high-redshift galaxy candidates with unexpectedly high stellar masses. An immediate concern is the consistency of these candidates with galaxy formation in the standard Λ CDM cosmological model, wherein the stellar mass ( M ⋆ ) of a galaxy is limited by the available baryonic reservoir of its host dark matter halo. The mass function of dark matter haloes therefore imposes an absolute upper limit on the number density n (> M ⋆ , z ) and stellar mass density ρ ⋆ (> M ⋆ , z ) of galaxies more massive than M ⋆ at any epoch z . Here I show that the most massive galaxy candidates in JWST observations at z ≈ 7–10 lie at the very edge of these limits, indicating an important unresolved issue with the properties of galaxies derived from the observations, how galaxies form at early times in Λ CDM or within this standard cosmology itself.
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- PAR ID:
- 10429698
- Date Published:
- Journal Name:
- Nature Astronomy
- Volume:
- 7
- Issue:
- 6
- ISSN:
- 2397-3366
- Page Range / eLocation ID:
- 731 to 735
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s41550-023-01937-7
