LATIS: Comparing Galaxy and IGM Tomography Maps as Tracers of Large-scale Structure and Protoclusters at $z \sim 2.5$

TL;DR

This study compares galaxy and IGM tomography maps at redshift 2.5 to understand large-scale structures and protoclusters, revealing potential UV-dim protoclusters missed by traditional surveys and emphasizing the need for further multi-wavelength follow-up.

Contribution

It demonstrates the effectiveness of combining IGM and galaxy maps to identify protoclusters and uncovers candidate UV-dim protoclusters that challenge existing galaxy detection methods.

Findings

IGM and galaxy maps are largely consistent in tracing large-scale structures.

Identification of candidate UV-dim protoclusters with no LBG overdensity.

Follow-up observations suggest these regions may host galaxies with low star formation.

Abstract

We investigate the consistency of intergalactic medium (IGM) tomography and galaxy surveys as tracers of the cosmic web and protoclusters at $z \sim 2.5$. We use maps from the Ly$\alpha$ Tomography IMACS Survey (LATIS), which trace the distributions of Lyman-break galaxies (LBGs) and IGM Ly$\alpha$ absorption on $\simeq 4$ $h^{-1}$ cMpc scales within the same large volume. Overall, the joint distribution of IGM absorption and LBG density is well constrained and accurately described by a simple physical model. However, we identify several exceptional locations exhibiting strong IGM absorption indicative of a massive protocluster, yet no coincident overdensity of LBGs. As discussed by Newman et al., whose results we revise using the complete LATIS survey data, these are candidate ultraviolet (UV)-dim protoclusters that may harbor distinct galaxy populations missed by rest-UV spectroscopic surveys. We present follow-up observations targeting one such candidate embedded within Antu, an extended region of IGM absorption at $z=2.685$ that contains five IGM-selected protoclusters and has a total mass of $3 \times 10^{15}~M_{\odot}$. Ly$\alpha$ emitters trace the overall structure of Antu but avoid the center of the candidate UV-dim protocluster, which also appears to contain no submillimeter-selected sources. A near-infrared spectroscopic galaxy census is needed to determine whether this large region is dominated by galaxies with reduced or absent star-formation activity. This work adds to a growing and puzzling literature on discrepancies among different galaxy and IGM tracers, whose resolution promises to shed light on the early stages of environment-dependent galaxy evolution.