ODIN: Where Do Lyman-alpha Blobs Live? Contextualizing Blob Environments within the Large-Scale Structure

TL;DR

This study uses a large survey to show that Lyman-alpha Blobs (LABs) are predominantly found in dense, filamentary regions of the early universe's large-scale structure, especially near protoclusters.

Contribution

It provides the first large-scale observational evidence linking LABs to specific cosmic web environments using extensive wide-field data.

Findings

LABs are located in higher-than-average density regions.

Approximately 70% of LABs are within 2.4 pMpc of a filament.

Protoclusters with LABs tend to have higher descendant masses.

Abstract

While many Lyman-alpha Blobs (LABs) are found in and around several well-known protoclusters at high redshift, how they trace the underlying large-scale structure is still poorly understood. In this work, we utilize 5,352 Lyman-alpha emitters (LAEs) and 129 LABs at z=3.1 identified over a $\sim$ 9.5 sq. degree area in early data from the ongoing One-hundred-deg$^2$ DECam Imaging in Narrowbands (ODIN) survey to investigate this question. Using LAEs as tracers of the underlying matter distribution, we identify overdense structures as galaxy groups, protoclusters, and filaments of the cosmic web. We find that LABs preferentially reside in regions of higher-than-average density and are located in closer proximity to overdense structures, which represent the sites of protoclusters and their substructures. Moreover, protoclusters hosting one or more LABs tend to have a higher descendant mass than those which do not. Blobs are also strongly associated with filaments of the cosmic web, with $\sim$ 70% of the population being within a projected distance of 2.4 pMpc from a filament. We show that the proximity of LABs to protoclusters is naturally explained by their association with filaments as large cosmic structures are where many filaments converge. The contiguous wide-field coverage of the ODIN survey allows us for the first time to firmly establish a connection between LABs as a population and their environment.