Revising Natal Kick Prescriptions in Population Synthesis Simulations

Abstract

Abstract Natal kicks are a matter of debate and they significantly affect the merger rate density of compact objects. Here, we present a new simple formalism for natal kicks of neutron stars (NSs) and black holes (BHs). We describe the magnitude of the kick as , where f H05 is a normalization factor, drawn from a Maxwellian distribution with one-dimensional rms velocity σ = 265 km s−1, m ej is the mass of the supernova (SN) ejecta, and m rem is the mass of the compact object. This formalism matches the proper motions of young Galactic pulsars and can naturally account for the differences between core-collapse SNe of single stars, electron-capture SNe and ultra-stripped SNe occurring in interacting binaries. Finally, we use our new kick formalism to estimate the local merger rate density of binary NSs (R BNS), BH–NS binaries (R BHNS), and binary BHs (R BBH), based on the cosmic star formation rate density and metallicity evolution. In our fiducial model, we find R BNS ∼ 600 Gpc−3 yr−1, R BHNS ∼ 10 Gpc−3 yr−1, and R BBH ∼ 50 Gpc−3 yr−1, fairly consistent with the numbers inferred from the LIGO–Virgo collaboration.