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Halving and Doubling: Boosting the Detection of Relativistic Effects in the Galaxy Bispectrum with Optimal Subsample Selection

Samantha Josephine Rossiter, Stefano Camera, Federico Montano, Chris Clarkson, Dionysios Karagiannis, Roy Maartens

Abstract

On the scale of the cosmic horizon, signatures that are unique to general relativity are concealed within the statistics of the large scale distribution of galaxies. These were thought to be beyond the reach of all but the most ambitious galaxy surveys, as they are substantially suppressed relative to standard redshift-space distortions. We show that the detectability of these higher-order relativistic effects can be dramatically enhanced by a sampling strategy that splits a galaxy catalogue into faint and bright subsamples and then combines their auto-bispectra. For current surveys such as DESI, this implies that this new signal will be detectable for the first time using our new strategy.

Halving and Doubling: Boosting the Detection of Relativistic Effects in the Galaxy Bispectrum with Optimal Subsample Selection

Abstract

On the scale of the cosmic horizon, signatures that are unique to general relativity are concealed within the statistics of the large scale distribution of galaxies. These were thought to be beyond the reach of all but the most ambitious galaxy surveys, as they are substantially suppressed relative to standard redshift-space distortions. We show that the detectability of these higher-order relativistic effects can be dramatically enhanced by a sampling strategy that splits a galaxy catalogue into faint and bright subsamples and then combines their auto-bispectra. For current surveys such as DESI, this implies that this new signal will be detectable for the first time using our new strategy.
Paper Structure (5 sections, 8 equations, 4 figures)

This paper contains 5 sections, 8 equations, 4 figures.

Table of Contents

  1. Introduction.
  2. Formalism.
  3. Subsample optimisation.
  4. Joint analysis of faint- and bright-subsample bispectra.
  5. Conclusions.

Figures (4)

  • Figure 1: Percentage difference of SNRs for the non-Newtonian faint- and bright-subsample bispectra compared to the bispectrum of the total sample, across different magnitude splits, $m_{\rm s}\in[18,19.8]$.
  • Figure 2: Histogram demonstrating the percentage increase of the total relativistic SNR for faint- and bright-subsamples and the F+B bispectra compared to the bispectrum of the total sample, across different magnitude splits, $m_{\rm s}\in[18,19.8]$. Dashed horizontal lines show the $5$ and $3\,\sigma$ detection significance thresholds.
  • Figure 3: Comparison of relativistic contributions to the relativistic bispectrum SNR, full GR and 2nd-order only. Shading corresponds to contributions grouped by scaling with powers of $\mathcal{H}/k$.
  • Figure 4: Comparison of the cumulative relativistic SNR for each sample analysis at the optimum magnitude split of $m_{\rm s}=18.4$ ($82 \%$ faint sources).