Euclid. V. The Flagship galaxy mock catalogue: a comprehensive simulation for the Euclid mission (2405.13495v1)

Abstract: We present the Flagship galaxy mock, a simulated catalogue of billions of galaxies designed to support the scientific exploitation of the Euclid mission. Euclid is a medium-class mission of the European Space Agency optimised to determine the properties of dark matter and dark energy on the largest scales of the Universe. It probes structure formation over more than 10 billion years primarily from the combination of weak gravitational lensing and galaxy clustering data. The breath of Euclid's data will also foster a wide variety of scientific analyses. The Flagship simulation was developed to provide a realistic approximation to the galaxies that will be observed by Euclid and used in its scientific analyses. We ran a state-of-the-art N-body simulation with four trillion particles, producing a lightcone on the fly. From the dark matter particles, we produced a catalogue of 16 billion haloes in one octant of the sky in the lightcone up to redshift z=3. We then populated these haloes with mock galaxies using a halo occupation distribution and abundance matching approach, calibrating the free parameters of the galaxy mock against observed correlations and other basic galaxy properties. Modelled galaxy properties include luminosity and flux in several bands, redshifts, positions and velocities, spectral energy distributions, shapes and sizes, stellar masses, star formation rates, metallicities, emission line fluxes, and lensing properties. We selected a final sample of 3.4 billion galaxies with a magnitude cut of H_E<26, where we are complete. We have performed a comprehensive set of validation tests to check the similarity to observational data and theoretical models. In particular, our catalogue is able to closely reproduce the main characteristics of the weak lensing and galaxy clustering samples to be used in the mission's main cosmological analysis. (abridged)

• The paper introduces a high-fidelity galaxy mock catalogue generated from a 4 trillion-particle N-body simulation spanning a 3600 Mpc box.
• It employs halo occupation and abundance matching techniques to assign realistic properties such as luminosity, color, and clustering to galaxies.
• Validation against observed lensing, number densities, and clustering statistics underpins its applicability for refining Euclid’s dark matter and dark energy studies.

Overview of the Euclid Flagship Galaxy Mock Catalogue

The Euclid Flagship Galaxy Mock Catalogue is an extensive synthetic dataset developed for optimizing and analyzing the Euclid mission—a project by the European Space Agency aimed at understanding the Universe's accelerated expansion through dark matter and dark energy investigations. This mock catalogue serves as a central tool for simulating galaxy observations expected from Euclid, relying on one of the largest $N$-body simulations to date, with a focus on weak gravitational lensing and galaxy clustering data. The Flagship simulation involves over four trillion particles distributed in a simulated Universe extending to a redshift of $z=3$, creating a comprehensive mock catalogue of galaxies derived from dark matter haloes.

Simulation Specifications

The backbone of the Flagship mock is an advanced $N$-body simulation executed on the Piz Daint supercomputer. It employs a computational box of 3600 $h^{-1}$ Mpc per side populated with $16,000^3$ particles, yielding a mass resolution of $10^9$ $h^{-1}\, M_{\odot}$. The simulation adheres to the Euclid reference cosmology, precisely modeling physical phenomena such as radiation and massive neutrinos. The lightcone generated provides a detailed all-sky particle lightcone where haloes are identified to simulate realistic galaxy distributions. These features ensure it meets the necessary volume and resolution requirements for tracing the faintest galaxies and the largest cosmological scales probed by Euclid.

Derivation of Galaxy Properties

The transformation of halo catalogues into a mock galaxy catalogue is accomplished by employing halo occupation distribution (HOD) models along with abundance matching techniques. Central and satellite galaxies are associated with dark matter haloes through a probabilistic framework calibrated against real-world observations, capturing essential galaxy properties such as luminosity, color, spectral energy distributions (SEDs), stellar masses, and emission lines. Furthermore, the mock implements realistic clustering and weak lensing signals essential for Euclid's cosmological probes.

Validation and Observational Reliability

Validation of the Flagship galaxy mock against empirical data spans several key observational aspects. The simulation's consistency with observed galaxy number densities, colours, luminosities, and clustering statistics demonstrates its reliability. It successfully captures the expected shear and galaxy-galaxy lensing correlations, providing a sound basis for anticipated Euclid mission analyses. These validations ensure that the Flagship mock accord with theoretical predictions while allowing for exploration of astrophysical phenomena on varying scales and characteristics.

Implications and Future Directions

This comprehensive simulation strategy sets a new standard for creating mock catalogues for next-generation cosmic surveys. The detailed dataset facilitates improvements in survey strategies, instrument calibration, and data analysis pipelines. It also serves as an anticipated benchmark for diverse scientific studies, ranging from galaxy evolution to further studies of gravitational lensing and dark matter distributions.

In future developments, enhancements targeting higher-resolution lensing maps and refined SED assignments could be envisaged. Moreover, addressing the incorporation of additional physical effects such as baryonic feedback and AGN influences would further increase the mock's utility for astrophysical studies beyond Euclid's primary science goals.

In summary, the Euclid Flagship Galaxy Mock Catalogue represents a significant advancement in synthetic astronomical datasets, ensuring the Euclid mission's capability to unravel some of the most profound topics in modern cosmology.