Characterizing Protoclusters and Protogroups at z 2.5 Using Lyα Tomography
Abstract
Ly-α tomography surveys have begun to produce three-dimensional (3D) maps of the intergalactic medium (IGM) opacity at z 2.5 with Mpc resolution. These surveys provide an exciting new way to discover and characterize high-redshift overdensities, including the progenitors of today's massive groups and clusters of galaxies, known as protogroups and protoclusters. We use the IllustrisTNG-300 hydrodynamical simulation to build mock maps that realistically mimic those observed in the Ly-α Tomographic IMACS Survey (LATIS). We introduce a novel method for delineating the boundaries of structures detected in 3D Ly-α flux maps by applying the watershed algorithm. We provide estimators for the dark matter masses of these structures (at z2.5), their descendant halo masses at z=0, and the corresponding uncertainties. We also investigate the completeness of this method for the detection of protogroups and protoclusters. Compared to earlier work, we apply and characterize our method over a wider mass range that extends to massive protogroups. We also assess the widely used fluctuating Gunn-Peterson approximation (FGPA) applied to dark-matter-only simulations; we conclude while it is adequate for estimating the Ly-α absorption signal from moderate-to-massive protoclusters ( 1014.2 M), it artificially merges a minority of lower-mass structures with more massive neighbors. Our methods will be applied to current and future Ly-α~tomography surveys to create catalogs of overdensities and study environment-dependent galaxy evolution in the Cosmic~Noon~era.
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