Euclid: Cosmological forecasts from the void size function

Abstract

The Euclid mission -with its spectroscopic galaxy survey covering a sky area over 15 000 deg 2 in the redshift range 0.9 < z < 1.8 -will provide a sample of tens of thousands of cosmic voids. This paper thoroughly explores for the first time the constraining power of the void size function on the properties of dark energy (DE) from a survey mock catalogue, the official Euclid Flagship simulation. We identify voids in the Flagship light-cone, which closely matches the features of the upcoming Euclid spectroscopic data set. We model the void size function considering a state-of-the art methodology: we rely on the volume conserving (Vdn) model, a modification of the popular Sheth & van de Weygaert model for void number counts, extended by means of a linear function of the large-scale galaxy bias. We find an excellent agreement between model predictions and measured mock void number counts. We compute updated forecasts for the Euclid mission on DE from the void size function and provide reliable void number estimates to serve as a basis for further forecasts of cosmological applications using voids. We analyse two different cosmological models for DE: the first described by a constant DE equation of state parameter, w, and the second by a dynamic equation of state with coefficients w 0 and w a . We forecast 1σ errors on w lower than the 10%, and we estimate an expected figure of merit (FoM) for the dynamical DE scenario FoM w 0 ,wa = 17 when considering only the neutrino mass as additional free parameter of the model. The analysis is based on conservative assumptions to ensure full robustness, and is a pathfinder for future enhancements of the technique. Our results showcase the impressive constraining power of the void size function from the Euclid spectroscopic sample, both as a stand-alone probe, and to be combined with other Euclid cosmological probes.

The halo bias inside cosmic voids

“…Our theoretical modeling of the HMF and halo bias may have several applications in data analyses exploiting the relation between the halo and dark matter distributions inside voids, as for instance measurements of the void size function 4 (Contarini et al 2019;Verza et al 2019;Contarini et al 2022). A further application could be represented by redshift-space distortions around voids, that in ongoing and upcoming galaxy surveys will provide impressive power in constraining the growth of structures and the expansion history of the Universe (Hamaus et al 2020;Nadathur et al 2020;Hamaus et al 2022).…”

“…halos with different minimum masses) we consider only voids for which the tracer density, averaged over a sphere of radius R eff /4, is less than the mean tracer density in the simulated comoving snapshot (box) at the redshift considered. Moreover, to avoid contamination from resolution effects (Verza et al 2019;Contarini et al 2022), we show our analysis only for voids with radius, R eff , larger than 2.5 the mean halo separation (mhs), i.e. R eff ≥ 2.5 × mhs, where mhs ≡ (N h /V ) −1/3 and N h is the total number of halos in a simulated box of volume V .…”

“…Recently, many cosmological statistics of cosmic voids have been explored, as for instance the void size function and void clustering which can probe the underlying cosmological model of the Universe (Pisani et al 2015;Hamaus et al 2015;Sahlén et al 2016;Cai et al 2016;Chuang et al 2017;Achitouv et al 2017;Hawken et al 2017;Hamaus et al 2017;Sahlén & Silk 2018;Achitouv 2019;Nadathur et al 2019;Kreisch et al 2019;Verza et al 2019;Pisani et al 2019;Hamaus et al 2020;Hawken et al 2020;Nadathur et al 2020;Aubert et al 2020;Bayer et al 2021;Kreisch et al 2021;Moresco et al 2022;Woodfinden et al 2022;Contarini et al 2022).…”

“…Cosmic voids are large underdense regions in the largescale structure of the Universe, span a large range of scales and constitute the largest observable objects in the Universe. Their size and underdense nature make them particularly suited to probe dark energy and modified gravity (Lee & Park 2009;Biswas et al 2010;Li & Efstathiou 2012;Clampitt et al 2013;Spolyar et al 2013;Cai et al 2015;Pisani et al 2015;Zivick et al 2015;Pollina et al 2016;Achitouv 2016;Sahlén et al 2016;Falck et al 2018;Sahlén & Silk 2018;Paillas et al 2019;Perico et al 2019;Verza et al 2019;Contarini et al 2021Contarini et al , 2022, massive neutrinos (Massara et al 2015;Banerjee & Dalal 2016;Kreisch et al 2019;Sahlén 2019;Schuster et al 2019;Zhang et al 2020;Kreisch et al 2021;Contarini et al 2022), primordial non-Gaussianity (Chan et al 2019), and physics beyond the standard model (Peebles 2001;Reed et al 2015;Yang et al 2015;Baldi & Villaescusa-Navarro 2016;Lester & Bolejko 2021;Arcari et al 2022).…”

Euclid: Forecasts from the void-lensing cross-correlation

“…This paper presents the first forecasts on cosmological parameters based on the combination of galaxy weak lensing, voidlensing cross-correlation, and angular void clustering, where voids are found in the galaxy photometric catalog of the Euclid survey, an ESA medium-class mission, currently scheduled for launch in 2023. The paper belongs to a series of companion papers investigating the scientific return that can be expected from voids from the Euclid mission (Hamaus et al 2021;Contarini et al 2022).…”