The Effect of Dark Matter–Dark Radiation Interactions on Halo Abundance: A Press–Schechter Approach

We study halo mass functions with the Press-Schechter formalism for interacting dark matter models, where matter power spectra are damped due to dark acoustic oscillations in the early universe. After adopting a smooth window function, we calibrate the analytical model with numerical simulations from the "effective theory of structure formation" (ETHOS) project and fix the model parameters in the high mass regime, $M_{\rm h}\gtrsim3\times10^{10}\;{\rm M}_{\odot}$. We also perform high-resolution cosmological simulations with halo masses down to $M_{\rm h}\sim10^8\;{\rm M}_{\odot}$ to cover a wide mass range for comparison. Although the model is calibrated with ETHOS1 and CDM simulations for high halo masses at redshift $z=0$, it successfully reproduces simulations for two other ETHOS models in the low mass regime at low and high redshifts. As an application, we compare the cumulative number density of haloes to that of observed galaxies at $z=6$, and find the interacting dark matter models with a kinetic decoupling temperature below $0.5\ \rm{keV}$ is disfavored. We also perform the abundance-matching analysis and derive the stellar-halo mass relation for these models at $z=4$. Suppression in halo abundance leads to less massive haloes that host observed galaxies in the stellar mass range $M_*\simeq 10^5-10^7\ {\rm M}_{\odot}$.