The population of merging compact binaries inferred using gravitational waves through GWTC-3

Kavli Affiliate: Chao-Lin Kuo

| First 5 Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, R. Abbott, T. D. Abbott

| Summary:

We report on the population properties of 76 compact binary mergers detected
with gravitational waves below a false alarm rate of 1 per year through GWTC-3.
The catalog contains three classes of binary mergers: BBH, BNS, and NSBH
mergers. We infer the BNS merger rate to be between 10 $rm{Gpc^{-3} yr^{-1}}$
and 1700 $rm{Gpc^{-3} yr^{-1}}$ and the NSBH merger rate to be between 7.8
$rm{Gpc^{-3}, yr^{-1}}$ and 140 $rm{Gpc^{-3} yr^{-1}}$ , assuming a constant
rate density versus comoving volume and taking the union of 90% credible
intervals for methods used in this work. Accounting for the BBH merger rate to
evolve with redshift, we find the BBH merger rate to be between 17.9
$rm{Gpc^{-3}, yr^{-1}}$ and 44 $rm{Gpc^{-3}, yr^{-1}}$ at a fiducial
redshift (z=0.2). We obtain a broad neutron star mass distribution extending
from $1.2^{+0.1}_{-0.2} M_odot$ to $2.0^{+0.3}_{-0.3} M_odot$. We can
confidently identify a rapid decrease in merger rate versus component mass
between neutron star-like masses and black-hole-like masses, but there is no
evidence that the merger rate increases again before 10 $M_odot$. We also find
the BBH mass distribution has localized over- and under-densities relative to a
power law distribution. While we continue to find the mass distribution of a
binary’s more massive component strongly decreases as a function of primary
mass, we observe no evidence of a strongly suppressed merger rate above $sim
60 M_odot$. The rate of BBH mergers is observed to increase with redshift at a
rate proportional to $(1+z)^{kappa}$ with $kappa = 2.9^{+1.7}_{-1.8}$ for
$zlesssim 1$. Observed black hole spins are small, with half of spin
magnitudes below $chi_i simeq 0.25$. We observe evidence of negative aligned
spins in the population, and an increase in spin magnitude for systems with
more unequal mass ratio.

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