Publication Date:
2019-09-07
Description:
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, $delta _{au _extrm{eff}}$, averaged over $15~h^{-1}, extrm{cMpc}$ scales, although scatter in the δm–$delta _{au _extrm{eff}}$ 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$
m 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 $15h^{-1}
m , cMpc$ scales, although these correspond to a wide range in mass overdensity. Assuming perfect removal of contamination by Ly α absorbers with damping wings, more than half of the remaining sightlines with $delta _{au _{
m eff}}gt 3.5$ trace protoclusters. It is furthermore possible to identify a model-dependent $delta _{au _{
m eff}}$ threshold that selects only protoclusters. However, such regions are rare: excluding absorption caused by damped systems, less than 0.1 per cent of sightlines that pass through a protocluster have $delta _{au _{
m eff}}gt 3.5$, meaning that any protocluster sample 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.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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