First star formation in ultra-light particle dark matter cosmology

Abstract

The formation of the first stars in the high-redshift Universe is a sensitive probe of the small-scale, particle physics nature of dark matter (DM). We carry out cosmological simulations of primordial star formation in ultra-light, axion-like particle DM cosmology, with masses of $10^{-22}$ and $10^{-21}\mathrm{eV}$, with de Broglie wavelengths approaching galactic scales ($\sim$kpc). The onset of star formation is delayed, and shifted to more massive host structures. For the lightest DM particle mass explored here, first stars form at $z\sim 7$ in structures with $\sim 10^9{\mathrm{M}}_{\odot }$, compared to the standard minihalo environment within the $\Lambda$ cold dark matter ($\Lambda$CDM) cosmology, where $z\sim 20-30$ and $\sim 10^5-10^6{\mathrm{M}}_{\odot }$. Despite this greatly altered DM host environment, the thermodynamic behaviour of the metal-free gas as it collapses into the DM potential well asymptotically approaches a very similar evolutionary track. Thus, the fragmentation properties are predicted to remain the same as in $\Lambda$CDM cosmology, implying a similar mass scale for the first stars. These results predict intense starbursts in the axion cosmologies, which may be amenable to observations with the {\it James Webb Space Telescope}.

5 pages, 1 table, 3 figures, accepted for publication in MNRAS

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• Constraining the non-gravitational scattering of baryons and dark matter with early cosmic structure formation