Cosmography with the Einstein Telescope

Abstract

Einstein Telescope (ET) is a 3rd generation gravitational-wave (GW) detector that is currently undergoing a design study. ET can detect millions of compact binary mergers up to redshifts 2-8. A small fraction of mergers might be observed in coincidence as gamma-ray bursts, helping to measure both the luminosity distance and red-shift to the source. By fitting these measured values to a cosmological model, it should be possible to accurately infer the dark energy equation-of-state, dark matter and dark energy density parameters. ET could, therefore, herald a new era in cosmology.

Figures (2)

• Figure 1: The left panel shows the range of the Einstein Telescope for inspiral signals from binaries as a function of the intrinsic (red solid line) and observed (blue dashed line) total mass. We assume that a source is visible if it produces an SNR of at least 8 in ET. The right panel shows a realization of the source catalogue showing the measured luminosity distance (inferred from GW observation of neutron star-black hole mergers) versus their red-shift (obtained by optical identification of the source). This catalogue is then fitted to a cosmological model.
• Figure 2: The plot on the left shows the distribution of errors in $\Omega_{\rm M},$$\Omega_{\Lambda}$ and $w,$ obtained by fitting 5,190 realizations of a catalogue of BNS merger events to a cosmological model of the type given in Eq. (\ref{['eq:cosmology']}), with three free parameters. The fractional 1-$\sigma$ width of the distributions $\sigma_{\Omega_{\rm M}}/\Omega_{\rm M}$, $\sigma_{\Omega_{\Lambda}}/\Omega_{\Lambda}$, and $\sigma_w/|w|,$ are 18%, 4.2% and 18% (with weak lensing errors in $D_{\rm L}$, left panels) and 14%, 3.5% and 15% (if weak lensing errors can be corrected, right panels). The plot on the right is the same, but assuming that $\Omega_\Lambda$ is known to be $\Omega_\Lambda=0.73$, and fitting the "data" to the model with two free parameters. The fractional 1-$\sigma$ widths in the distribution $\sigma_{\Omega_{\rm M}}/\Omega_{\rm M}$ and and $\sigma_w/|w|$, are 9.4% and 7.6% (with weak lensing errors in $D_{\rm L}$, left panels) and 8.1% and 6.6% (if weak lensing errors can be corrected, right panels).