Characterizing Protoclusters and Protogroups at z ∼ 2.5 Using Lyα Tomography

• Published in: The Astrophysical journal Vol. 930; no. 2; pp. 109 - 126
• Main Authors: Qezlou, Mahdi, Newman, Andrew B., Rudie, Gwen C., Bird, Simeon
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.05.2022; IOP Publishing
• Subjects: Algorithms; Astrophysics; Dark matter; Dark matter density; Dark matter distribution; Galactic clusters; Galactic evolution; Galaxies; Galaxy environments; Intergalactic media; Intergalactic medium; Large-scale structure of the universe; Lyman alpha forest; Magnetohydrodynamical simulations; Opacity; Polls & surveys; Protoclusters; Red shift; Tomography
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac6259

Abstract Ly α tomography surveys have begun to produce 3D maps of the intergalactic medium opacity at z ∼ 2.5 with megaparsec 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. 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 z ∼ 2.5), 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 applied to dark-matter-only simulations; we conclude that while it is adequate for estimating the Ly α absorption signal from moderate-to-massive protoclusters (≳10 14.2 h −1 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 galactic evolution in the Cosmic Noon era.