We contrast predictions for the high-redshift galaxy population and reionization history between cold dark matter ( CDM ) and an alternative self-interacting dark matter model based on the recently developed ETHOS framework that alleviates the small-scale CDM challenges within the Local Group .
We perform the highest resolution hydrodynamical cosmological simulations ( a 36 Mpc ^ { 3 } volume with gas cell mass of \sim 10 ^ { 5 } { M _ { \odot } } and minimum gas softening of \sim 180 pc ) within ETHOS to date – plus a CDM counterpart – to quantify the abundance of galaxies at high redshift and their impact on reionization .
We find that ETHOS predicts galaxies with higher ultraviolet ( UV ) luminosities than their CDM counterparts and a faster build-up of the faint end of the UV luminosity function .
These effects , however , make the optical depth to reionization less sensitive to the power spectrum cut-off : the ETHOS model differs from the CDM \tau value by only 10 per cent and is consistent with Planck limits if the effective escape fraction of UV photons is 0.1-0.5 .
We conclude that current observations of high-redshift luminosity functions can not differentiate between ETHOS and CDM models , but deep JWST surveys of strongly-lensed , inherently faint galaxies have the potential to test non-CDM models that offer attractive solutions to CDM ’ s Local Group problems .