ODIN: Where Do Lyα Blobs Live? Contextualizing Blob Environments within Large-scale Structure

Abstract

While many Ly α 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 5352 Ly α emitters (LAEs) and 129 LABs at z = 3.1 identified over a ∼9.5 deg ^2 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 ∼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 to establish firmly a connection between LABs as a population and filaments of the cosmic web for the first time.

Keywords

• High-redshift galaxy clusters
• Galaxy clusters
• Lyman-alpha galaxies