Modeling the core-halo mass relation in fuzzy dark matter halos

Fuzzy dark matter (FDM) is an intriguing candidate alternative to the standard cold dark matter (CDM). The FDM model predicts that dark halos have characteristic core structures generated by the effect of quantum pressure, which is different from the structure of CDM halos. We devise a semianalytic model of an FDM halo density profile by assuming that the density distribution results from the redistribution of mass in a halo with the Navarro–Frenk–White profile. We calculate the mass redistribution radius by considering dynamical relaxation within the FDM halo. We adopt a concentration-halo mass relation with lower concentration compared to that in the CDM model below the half mode mass, which originates from the suppressed matter density fluctuations at small length scales. Our model reproduces the core-halo mass relation (CHMR) found in the numerical simulation of Schive et al. [Nat. Phys. 10, 496 (2014).] at $z<1$. We show that the CHMR is well described by a double power law, unlike previous studies that approximate it by a single power law. Our model predictions are in reasonable agreement with the results of the largest FDM simulation of May and Springel [Mon. Not. R. Astron. Soc. 506, 2603 (2021).] at $z=3$. We find that the core mass for a given halo mass follows the log-normal distribution, both in our model and in the simulation results for the first time, and quantitatively compare the variance of the distribution among them. Although our model does not fully explain the scatter of the CHMR, we show the scatter of the concentration-halo mass relation sizably contributes to them.