Cosmology with LIGO/Virgo dark sirens: Hubble parameter and modified gravitational wave propagation

Abstract

We present a detailed study of the methodology for correlating 'dark sirens' (compact binaries coalescences without electromagnetic counterpart) with galaxy catalogs. We propose several improvements on the current state of the art, and we apply them to the GWTC-2 catalog of LIGO/Virgo gravitational wave (GW) detections, and the GLADE galaxy catalog, performing a detailed study of several sources of systematic errors that, with the expected increase in statistics, will eventually become the dominant limitation. We provide a measurement of H 0 from dark sirens alone, finding as the best result H 0 = 67.3 +27.6 −17.9 km s −1 Mpc −1 (68% c.l.) which is, currently, the most stringent constraint obtained using only dark sirens. Combining dark sirens with the counterpart for GW170817 we find H 0 = 72.2 +13.9 −7.5 km s −1 Mpc −1 . We also study modified GW propagation, which is a smoking gun of dark energy and modifications of gravity at cosmological scales, and we show that current observations of dark sirens already start to provide interesting limits. From dark sirens alone, our best result for the parameter Ξ 0 that measures deviations from GR (with−1.2 . We finally discuss limits on modified GW propagation under the tentative identification of the flare ZTF19abanrhr as the electromagnetic counterpart of the binary black hole coalescence GW190521, in which case our most stringent result is Ξ 0 = 1.8 +0.9 −0.6 . We release the publicly available code DarkSirensStat, which is available under open source license at https://github.com/CosmoStatGW/DarkSirensStat.

A pixelated approach to galaxy catalogue incompleteness: improving the dark siren measurement of the Hubble constant

“…And if the resolution of the catalogue was increased at some point in the future, the number of out-of-catalogue calculations required would not increase, allowing incredibly high resolution of features such as empty patches and boundaries between surveys, with no extra computational cost. Following a similar approach to Finke et al (2021), and computing a completeness map (but in terms of th ) that assigns pixels to groups of similar completeness would be one way to do this. In summary, the pixelated analysis demonstrated in this paper shows a clear improvement on the analysis in Abbott et al (2021b).…”

“…The contribution from an individual event is less informative than in the counterpart case, but combining information from multiple events reduces the uncertainty and allows an additional constraint on 0 to be made (see, e.g. MacLeod & Hogan (2008); Chen et al (2018); Fishbach et al (2019); Soares-Santos et al (2019); Gray et al (2020); Abbott et al (2020); Palmese et al (2020); Vasylyev & Filippenko (2020); Finke et al (2021). An alternative, cross-correlating GW events with galaxies of known redshift, is presented in Mukherjee et al (2021)).…”

“…The issue of non-uniform catalogue incompleteness was addressed in Finke et al (2021), in which areas of the sky with similar levels of completeness were grouped together, and a completeness correction was applied. The methods of completeness correction used in Finke et al (2021) differ to the one used here (and in Gray et al (2020); Abbott et al (2021b)), where the limiting magnitude of the telescope is used to assess the probability of any galaxy being 'seen'.…”

“…The issue of non-uniform catalogue incompleteness was addressed in Finke et al (2021), in which areas of the sky with similar levels of completeness were grouped together, and a completeness correction was applied. The methods of completeness correction used in Finke et al (2021) differ to the one used here (and in Gray et al (2020); Abbott et al (2021b)), where the limiting magnitude of the telescope is used to assess the probability of any galaxy being 'seen'. Under the same set of assumptions these two methods should give consistent results, however the methodology outlined here allows for a more complete treatment of the GW mass priors (see section 3.1 for details), including consistency between the prior applied to individual events and the prior used to compute GW selection effects, which is necessary for an unbiased estimate of 0 .…”

A Pixelated Approach to Galaxy Catalogue Incompleteness: Improving the Dark Siren Measurement of the Hubble Constant

“…The contribution from an individual event is less informative than in the counterpart case, but combining information from multiple events reduces the uncertainty and allows an additional constraint on 𝐻 0 to be made (see, e.g. MacLeod & Hogan (2008); Chen et al (2018); Fishbach et al (2019); Soares-Santos et al (2019); Gray et al (2020); Abbott et al (2020); Palmese et al (2020); Vasylyev & Filippenko (2020); Finke et al (2021)). One important aspect of this method is acknowledging that galaxy catalogues are incomplete, and therefore may not contain the real host galaxy of the GW event.…”