Publication
Searching for the shadows of giants: characterizing protoclusters with line of sight Lyman-α absorption
Publisher:
Oxford University Press (OUP)
Date:
07-09-2019
DOI:
10.1093/MNRAS/STZ2504
Abstract: We use state-of-the-art hydrodyamical simulations from the Sherwood, EAGLE, and Illustris projects to examine the signature of Mz = 0 ≃ 1014 M⊙ protoclusters observed in Ly α absorption at z ≃ 2.4. We find that there is a weak correlation between the mass overdensity, δm, and the Ly α effective optical depth relative to the mean, $\\delta _{\\tau _\\textrm{eff}}$, averaged over $15~h^{-1}\\, \\textrm{cMpc}$ scales, although scatter in the δm–$\\delta _{\\tau _\\textrm{eff}}$ plane means it is not possible to uniquely identify large-scale overdensities with strong Ly α absorption. Although all protoclusters are associated with large-scale mass overdensities, most sightlines through protoclusters in a ∼106$\\rm cMpc^{3}$ volume probe the low column density Ly α forest. A small subset of sightlines that pass through protoclusters exhibit coherent, strong Ly α absorption on $15h^{-1}\\rm \\, cMpc$ scales, although these correspond to a wide range in mass overdensity. Assuming perfect removal of contamination by Ly α absorbers with d ing wings, more than half of the remaining sightlines with $\\delta _{\\tau _{\\rm eff}}\\gt 3.5$ trace protoclusters. It is furthermore possible to identify a model-dependent $\\delta _{\\tau _{\\rm eff}}$ threshold that selects only protoclusters. However, such regions are rare: excluding absorption caused by d ed systems, less than 0.1 per cent of sightlines that pass through a protocluster have $\\delta _{\\tau _{\\rm eff}}\\gt 3.5$, meaning that any protocluster s le selected in this manner will also be highly incomplete. On the other hand, coherent regions of Ly α absorption also provide a promising route for identifying and studying filamentary environments at high redshift.