Simulating kilonovae in the ΛCDM universe

Abstract

ABSTRACT Kilonovae are optical flashes produced in the aftermath of neutron star–neutron star mergers or neutron star–black hole mergers. In this work, we use the Millennium Simulation, combined with semi-analytic galaxy formation model gabe (Galaxy Assembly with Binary Evolution) to explore the cosmic event rate of kilonovae, and the properties of their host galaxies in a cosmological context. We find that model with supernova kick velocity of $V_{\rm kick}=0\, \, {\rm km}\, \, {\rm s}^{-1}$ fits the observation best, satisfying the preference for low kick velocity binary system in theoretical models. With $V_{\rm kick}=0\, \, {\rm km}\, \, {\rm s}^{-1}$, the cosmic event rate of NNMs and NBMs at z = 0 are 283 and $91\, \, {\rm Gpc}^{-3}\, \, {\rm yr}^{-1}$, respectively, marginally consistent with the constraint from LVC GWTC-1. For Milky Way-mass galaxies, we predict the NNM rate is $25.7^{+59.6}_{-7.1}\, {\rm Myr}^{-1}$, which is also in good agreement with the observed properties of binary neutron stars in the Milky Way. Taking all the kilonovae into account in the history of Milky Way-mass galaxies, we find that the averaged r-process elements yield (A > 79) in an NNM/NBM event should be $0.01\, {\rm M}_\odot$ to be consistent with observation. We conclude that NGC 4993, the host galaxy of GW170817, is a typical host galaxy for NNMs. However, generally, NNMs and NBMs tend to reside in young, blue, star-forming, late-type galaxies, with stellar mass, and gaseous metallicity distribution peaking at $M_{\rm *}=10^{10.65}\, {\rm M}_\odot$ and 12 + log (O/H) = 8.72 − 8.85, respectively. By exploring the connection between kilonovae and their host galaxies in the cosmological background, it is promising to constrain model better when we have more events in the forthcoming future.