Searching for the shadows of giants: characterizing protoclusters with line of sight Lyman-α absorption
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, δ _{τ_{eff}}, averaged over 15 h^{-1} cMpc scales, although scatter in the δm-δ _{τ_{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 ∼106cMpc3 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} 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 δ _{τ_eff}> 3.5 trace protoclusters. It is furthermore possible to identify a model-dependent δ _{τ_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 δ _{τ_eff}> 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2019
- DOI:
- 10.1093/mnras/stz2504
- arXiv:
- arXiv:1909.02513
- Bibcode:
- 2019MNRAS.489.5381M
- Keywords:
-
- galaxies: clusters: general;
- intergalactic medium;
- quasars: absorption lines;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 18 pages, 18 figures, 3 tables