Probing Large-scale Structure and the Multi-Phase IGM at the Cosmic Noon -- Insights from a Joint Survey with Euclid, CSST, JPCam, and JUST

TL;DR

This paper proposes a coordinated multi-instrument survey to study the multi-phase IGM and CGM at cosmic noon, enhancing photometric redshift accuracy and mapping large-scale structures, with simulations indicating the potential and limitations of current methods.

Contribution

It introduces a novel integrated survey framework combining Euclid, CSST, JPCam, and JUST data to probe the IGM and CGM at cosmic noon, including new simulation-based assessments.

Findings

Narrow-band photometry improves photo-z accuracy for star-forming galaxies.

Mock data shows successful reconstruction of large-scale structures from Lyalpha forest.

Detecting diffuse Mg II absorption remains challenging with current instruments.

Abstract

We present scientific and technical justifications of a potential coordinated Euclid/CSST/JPCam/JUST survey of the Euclid Deep Field North (EDF-N), aimed at probing the multi-phase circumgalactic and intergalactic medium (CGM/IGM) at the cosmic noon over ~20 deg$^2$. The survey is structured around three connected goals: (1) improving photometric redshift (photo-z) accuracy through the combination of broad- and narrow-band photometry, enabling reliable identification of large-scale structures; (2) probing extended CGM emission with dedicated narrow-band imaging; and (3) mapping foreground IGM via absorption-line spectroscopy of background galaxies. Together, these components establish an integrated observational framework to investigate galactic ecosystems -- linking galaxies to their circumgalactic and intergalactic environments -- at cosmic noon. We show that the J-PAS-like narrow-band system used in JPCam substantially improves photo-z accuracies from only the Euclid/CSST broad-band data, especially for star-forming galaxies at z~1.0-1.4. This enables the identification of galaxy groups and (proto-)clusters directly from photo-z measurements. Stacked JPCam narrow-band imaging should also detect extended [O II]-emitting CGM halos. We then construct mock 3D gas distribution model and realistic galaxy catalog, and further construct mock CSST and JUST background galaxy spectra adding Lyalpha and Mg II absorptions. The reconstructed 3D H I field from CSST Lyalpha forest reliably recovers large-scale structures; however, our simulations indicate that detecting diffuse IGM Mg II absorption with JUST is infeasible, either through spectral stacking or via the two-point correlation function method. We conclude that constraining the metallicity of the diffuse IGM will require significantly deeper and higher-resolution spectroscopy expected from future facilities such as the 39 m E-ELT.