The Cosmic Merger Rate Density Evolution of Compact Binaries Formed in Young Star Clusters and in Isolated Binaries
Abstract
Next generation groundbased gravitationalwave detectors will observe binary black hole (BBH) mergers up to redshift $z\gtrsim 10$ , probing the evolution of compact binary (CB) mergers across cosmic time. Here, we present a new datadriven model to estimate the cosmic merger rate density (MRD) evolution of CBs, by coupling catalogs of CB mergers with observational constraints on the cosmic star formation rate (SFR) density and on the metallicity evolution of the universe. We adopt catalogs of CB mergers derived from recent Nbody and populationsynthesis simulations, to describe the MRD of CBs formed in young star clusters (hereafter, dynamical CBs) and in the field (hereafter, isolated CBs). The local MRD of dynamical BBHs is ${{ \mathcal R }}_{\mathrm{BBH}}={64}_{20}^{+34}$ Gpc^{3} yr^{1}, consistent with the 90% credible interval from the first and second observing runs (O1 and O2) of the LIGOVirgo collaboration, and with the local MRD of isolated BBHs ( ${{ \mathcal R }}_{\mathrm{BBH}}={50}_{37}^{+71}$ Gpc^{3} yr^{1}). The local MRD of dynamical and isolated black holeneutron star binaries is ${{ \mathcal R }}_{\mathrm{BHNS}}={41}_{23}^{+33}$ and ${49}_{34}^{+48}$ Gpc^{3} yr^{1}, respectively. Both values are consistent with the upper limit inferred from O1 and O2. Finally, the local MRD of dynamical binary neutron stars (BNSs, ${{ \mathcal R }}_{\mathrm{BNS}}={151}_{38}^{+59}$ Gpc^{3} yr^{1}) is a factor of two lower than the local MRD of isolated BNSs ( ${{ \mathcal R }}_{\mathrm{BNS}}={283}_{75}^{+97}$ Gpc^{3} yr^{1}). The MRD for all CB classes grows with redshift, reaching its maximum at $z\in [1.5,2.5]$ , and then decreases. This trend springs from the interplay between cosmic SFR, metallicity evolution, and delay time of binary compact objects.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 2020
 DOI:
 10.3847/15384357/ab9b78
 arXiv:
 arXiv:2004.09533
 Bibcode:
 2020ApJ...898..152S
 Keywords:

 Gravitational waves;
 Astrophysical black holes;
 Neutron stars;
 Star formation;
 Binary stars;
 678;
 98;
 1108;
 1569;
 154;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 11 pages, 5 figures, 1 table, accepted for publication in ApJ