First star formation in ultralight particle dark matter cosmology

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 ultralight, axion-like particle DM cosmology, with masses of 10(-22) and 10(-21) eV, with de Broglie wavelengths approaching galactic scales (similar to 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 similar to 7 in structures with similar to 10(9) M-circle dot, compared to the standard minihalo environment within the Lambda cold dark matter (Lambda CDM) cosmology, where z similar to 20-30 and similar to 10(5)-10(6)M(circle dot). 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 James Webb Space Telescope.