Halo abundance and assembly history with extreme-axion wave dark matter at z ≥ 4

Wave dark matter (psi DM) composed of extremely light bosons (m(psi) similar to 10(-22) eV), with quantum pressure suppressing structures below a kpc-scale de Broglie wavelength, has become a viable dark matter candidate. Compared to the conventional free-particle psi DM(FP psi DM), the extreme-axion psi DM model (EA psi DM) proposed by Zhang & Chiueh features a larger cut-off wavenumber and a broad spectral bump in the matter transfer function. Here, we conduct cosmological simulations to compare the halo abundances and assembly histories at z = 4-11 between three different scenarios: FP psi DM, EA psi DM and cold dark matter (CDM). We show that EA psi DM produces significantly more abundant low-mass haloes than FP psi DM with the same m(psi), and therefore could alleviate the tension in m(psi) required by the Ly alpha forest data and by the kpc-scale dwarf galaxy cores. We also find that, compared to the CDM counterparts, massive EA psi DM haloes are, on average, 3-4 times more massive at z = 10-11 due to their earlier formation, undergo a slower mass accretion at 7 less than or similar to z less than or similar to 11, and then show a rapidly rising major merger rate exceeding CDM by similar to 50 per cent at 4 less than or similar to z less than or similar to 7. This fact suggests that EA psi DM haloes may exhibit more prominent starbursts at z <= 7.