Exploring compact binary populations with the Einstein Telescope

Abstract

The Einstein Telescope (ET), a wide-band, future third generation gravitational wave detector, is expected to have detection rates of $\sim 10^5 - 10^6$ binary black hole (BBH) detections and $\sim 7 \times 10^4$ binary neutron star (BNS) detections in one year. The coalescence of compact binaries with a total mass of 20 - 100 $M_{\odot}$, typical of BH-BH or BH-NS binaries, will be visible up to redshift $z\approx 20$ and even higher, thus facilitating the understanding of the dark era of the Universe preceding the birth of the first stars. The ET will therefore be a crucial instrument for population studies. We analysed the compact binaries originating in stars from (i) Population (Pop) I+II, (ii) Pop III, and (iii) globular clusters (GCs), with the single ET instrument, using the ET-D design sensitivity for the analysis. We estimated the constraints on the chirp mass, redshift, and merger rate as function of redshift for these classes of compact object binaries. We conclude that the ET as a single instrument is capable of detecting and distinguishing different compact binary populations separated in chirp mass - redshift space. While compact binaries originating in stars from Pop III are clearly distinguishable, owing to the separation in chirp mass - redshift space, the other two populations, Pop I+II, and GCs, can be distinguished with just 500 detections, corresponding to an observation time of $\sim 1$ hr. The mass distribution characteristics of such different compact binary populations can also be estimated with the single ET instrument.