Semi-analytic forecasts for Roman -- the beginning of a new era of deep-wide galaxy surveys

TL;DR

This paper presents extensive semi-analytic galaxy lightcone simulations tailored for the upcoming Roman Space Telescope, enabling forecasts of galaxy survey outcomes and optimization strategies for deep-wide galaxy surveys.

Contribution

It introduces five large-scale simulated galaxy lightcones with over 25 million galaxies, specifically designed for Roman, Euclid, and Rubin surveys, to forecast survey performance and improve scientific planning.

Findings

Forecasts for galaxy number density and cosmic SFR improve with survey size.

Field-to-field variance and galaxy clustering are quantified for future surveys.

Comparison of semi-analytic and empirical models highlights differences in galaxy property predictions.

Abstract

The Nancy Grace Roman Space Telescope, NASA's next flagship observatory, will redefine deep-field galaxy survey with a field of view two orders of magnitude larger than Hubble and an angular resolution of matching quality. These future deep-wide galaxy surveys necessitate new simulations to forecast their scientific output and to optimise survey strategies. In this work, we present five realizations of 2-deg^2 lightcones, containing a total of >25 million simulated galaxies with -16 < MUV < -25 spanning z ~ 0 to 10. This dataset enables a new set of experiments with the impacts of survey size on the derived galaxy formation and cosmological constraints. The intrinsic and observable galaxy properties are predicted using a well-established, physics-based semi-analytic modelling approach. We provide forecasts for number density, cosmic SFR, field-to-field variance, and angular two-point correlation functions, and demonstrate how the future wide-field surveys will be able to improve these measurements relative to current generation surveys. We also present a comparison between these lightcones and others that have been constructed with empirical models. The mock lightcones are designed to facilitate the exploration of multi-instrument synergies and connecting with current generation instruments and legacy surveys. In addition to Roman, we also provide photometry for a number of other instruments on upcoming facilities, including Euclid and Rubin, as well as the instruments that are part of many legacy surveys. Full object catalogues and data tables for the results presented in this work are made available through a web-based, interactive portal https://www.simonsfoundation.org/semi-analytic-forecasts.