Euclid: Forecasts from redshiftspace distortions and the AlcockPaczynski test with cosmic voids
Abstract
Euclid is poised to survey galaxies across a cosmological volume of unprecedented size, providing observations of more than a billion objects distributed over a third of the full sky. Approximately 20 million of these galaxies will have their spectroscopy available, allowing us to map the threedimensional largescale structure of the Universe in great detail. This paper investigates prospects for the detection of cosmic voids therein and the unique benefit they provide for cosmological studies. In particular, we study the imprints of dynamic (redshiftspace) and geometric (AlcockPaczynski) distortions of average void shapes and their constraining power on the growth of structure and cosmological distance ratios. To this end, we made use of the Flagship mock catalog, a stateoftheart simulation of the data expected to be observed with Euclid. We arranged the data into four adjacent redshift bins, each of which contains about 11 000 voids and we estimated the stacked voidgalaxy crosscorrelation function in every bin. Fitting a lineartheory model to the data, we obtained constraints on f/b and D_{M}H, where f is the linear growth rate of density fluctuations, b the galaxy bias, D_{M} the comoving angular diameter distance, and H the Hubble rate. In addition, we marginalized over two nuisance parameters included in our model to account for unknown systematic effects in the analysis. With this approach, Euclid will be able to reach a relative precision of about 4% on measurements of f/b and 0.5% on D_{M}H in each redshift bin. Better modeling or calibration of the nuisance parameters may further increase this precision to 1% and 0.4%, respectively. Our results show that the exploitation of cosmic voids in Euclid will provide competitive constraints on cosmology even as a standalone probe. For example, the equationofstate parameter, w, for dark energy will be measured with a precision of about 10%, consistent with previous more approximate forecasts.
This paper is published on behalf of the Euclid Consortium.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 2022
 DOI:
 10.1051/00046361/202142073
 arXiv:
 arXiv:2108.10347
 Bibcode:
 2022A&A...658A..20H
 Keywords:

 cosmology: observations;
 cosmological parameters;
 dark energy;
 largescale structure of Universe;
 methods: data analysis;
 surveys;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 15 pages, 7 figures. Accepted by A&