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Searching for the shadows of giants: characterizing protoclusters with line of sight Lyman-? absorption

Miller, Joel S A; Bolton, James S; Hatch, Nina


Joel S A Miller

Associate Professor


© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. 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, δτeff, averaged over 15 h−1 cMpc scales, although scatter in the δm–δτeff 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 cMpc3 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 δτeff > 3.5 trace protoclusters. It is furthermore possible to identify a model-dependent δτeff 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 δτeff > 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.


Miller, J. S. A., Bolton, J. S., & Hatch, N. (2019). Searching for the shadows of giants: characterizing protoclusters with line of sight Lyman-? absorption. Monthly Notices of the Royal Astronomical Society, 489(4), 5381-5397.

Journal Article Type Article
Acceptance Date Sep 5, 2019
Online Publication Date Sep 7, 2019
Publication Date 2019-11
Deposit Date Sep 16, 2019
Publicly Available Date Sep 24, 2019
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 489
Issue 4
Pages 5381-5397
Keywords Space and Planetary Science; Astronomy and Astrophysics
Public URL
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Additional Information This is a pre-copyedited, author-produced PDF of an article accepted for publication in [insert journal title] following peer review. The version of record [insert complete citation information here] is available online at: xxxxxxx [insert URL that the author will receive upon publication here].


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