Formation of mass gap compact object and black hole binary from Population III stars

Abstract

We performed population synthesis simulations of Population III binary stars with Maxwellian kick velocity distribution when MGCOs (Mass Gap Compact Objects with mass 2--5$\,M_{\odot}$) are formed. We found that for eight kick velocity dispersion models of $σ_{\rm k}=0$--$500$ km/s, the mean mass of black hole (BH)-MGCO binary is $\sim (30 \,M_\odot,\,2.6 \,M_\odot)$. In numerical data of our simulations, we found the existence of BH-MGCO binary with mass $(22.9 \,M_\odot,\,2.5 \,M_\odot)$ which looks like GW190814.

Figures (6)

• Figure 1: The chirp mass distribution of BH-MGCO binaries which merge within the Hubble time for 8 kick models with $\sigma_{\rm k}=0,~100,~150,~200,~265,~300,~400$, and $500$ km/s, where $N_{\rm total}=10^6$ is the total number of binaries which we have simulated. The chirp mass distribution does not strongly depend on the kick velocity. The averaged individual masses are summarized in Table \ref{['tab:ER']}.
• Figure 2: The merger rate densities for 7 kick models with $\sigma_{\rm k}=100,~150,~200,~265,~300,~400$, and $500$ km/s. We note that the smaller kick velocity model, the lower redshift the peak of merger rate is.
• Figure 3: Evolutionary path of a Pop III BH-MGCO binary similar to GW190814. MS, CHeB, HeSB, and nHe mean the main sequence, Core He burning, He shell burning, and naked He stars, respectively. The naked He star is the remnant after the common envelope phase. $V_{\rm orb}$, and $V_{\rm kick}$ are the orbital velocity just before the SN, and the natal kick velocity, respectively. $a$ (in the solar radius $R_{\odot}$) and $e$ denote the orbital separation and eccentricity, respectively.
• Figure 4: Strain-noise fitted curves for 4 GW detector configurations: LIGO O3a-Livingston (O3a-L, green), LIGO O5 (O5, magenta), Einstein Telescope (ET-B) (red) and Cosmic Explorer (CE2) (purple). These fitting curves are obtained by using Refs. Aasi:2013wyaHild:2008ngMishra:2010tpReitze:2019iox. We have lower frequency cutoffs of 10 Hz, 1 Hz and 5 Hz for O3a-L and O5, ET-B and CE2, respectively.
• Figure 5: Mass distributions of MGCOs which merge within the Hubble time for 8 kick models with $\sigma_{\rm k}=0,~100,~150,~200,~265,~300,~400$, and $500$ km/s. We find that the lighter BHs can have various masses.