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Title: Characterizing the pressure smoothing scale of the intergalactic medium

Abstract

The thermal state of the intergalactic medium (IGM) at z < 6 constrains the nature and timing of cosmic reionization events, but its inference from the Lyα forest is degenerate with the 3D structure of the IGM on ∼100 kpc scales, where, analogous to the classical Jeans argument, the pressure of the T ≃ 10{sup 4} K gas supports it against gravity. We simulate the IGM using smoothed particle hydrodynamics, and find that, at z < 6, the gas density power spectrum does not exhibit the expected filtering scale cutoff, because dense gas in collapsed halos dominates the small-scale power masking pressure smoothing effects. We introduce a new statistic, the real-space Lyα flux, F{sub real}, which naturally suppresses dense gas, and is thus robust against the poorly understood physics of galaxy formation, revealing pressure smoothing in the diffuse IGM. The F{sub real} power spectrum is accurately described by a simple fitting function with cutoff at λ{sub F}, allowing us to rigorously quantify the pressure smoothing scale for the first time: we find λ{sub F} = 79 kpc (comoving) at z = 3 for our fiducial thermal model. This statistic has the added advantage that it directly relates to observations ofmore » correlated Lyα forest absorption in close quasar pairs, recently proposed as a method to measure the pressure smoothing scale. Our results enable one to quantify the pressure smoothing scale in simulations, and ask meaningful questions about its dependence on reionization and thermal history. Accordingly, the standard description of the IGM in terms of the amplitude T{sub 0} and slope γ of the temperature–density relation T=T{sub 0}(ρ/ ρ-bar ){sup γ−1} should be augmented with a third pressure smoothing scale parameter λ{sub F}.« less

Authors:
;  [1]; ;  [2];  [3]
  1. Institute of Astronomy and Kavli Institute of Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  2. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
  3. Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
22882501
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 812; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; Journal ID: ISSN 0004-637X
Country of Publication:
United Kingdom
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; COMPUTERIZED SIMULATION; DENSITY; GALAXIES; GRAVITATION; HYDRODYNAMICS; INTERGALACTIC SPACE; QUASARS; RED SHIFT; SPECTRA; STARS; STATISTICS; UNIVERSE

Citation Formats

Kulkarni, Girish, Rorai, Alberto, Hennawi, Joseph F., Oñorbe, Jose, and Springel, Volker. Characterizing the pressure smoothing scale of the intergalactic medium. United Kingdom: N. p., 2015. Web. doi:10.1088/0004-637X/812/1/30.
Kulkarni, Girish, Rorai, Alberto, Hennawi, Joseph F., Oñorbe, Jose, & Springel, Volker. Characterizing the pressure smoothing scale of the intergalactic medium. United Kingdom. https://doi.org/10.1088/0004-637X/812/1/30
Kulkarni, Girish, Rorai, Alberto, Hennawi, Joseph F., Oñorbe, Jose, and Springel, Volker. Sat . "Characterizing the pressure smoothing scale of the intergalactic medium". United Kingdom. https://doi.org/10.1088/0004-637X/812/1/30.
@article{osti_22882501,
title = {Characterizing the pressure smoothing scale of the intergalactic medium},
author = {Kulkarni, Girish and Rorai, Alberto and Hennawi, Joseph F. and Oñorbe, Jose and Springel, Volker},
abstractNote = {The thermal state of the intergalactic medium (IGM) at z < 6 constrains the nature and timing of cosmic reionization events, but its inference from the Lyα forest is degenerate with the 3D structure of the IGM on ∼100 kpc scales, where, analogous to the classical Jeans argument, the pressure of the T ≃ 10{sup 4} K gas supports it against gravity. We simulate the IGM using smoothed particle hydrodynamics, and find that, at z < 6, the gas density power spectrum does not exhibit the expected filtering scale cutoff, because dense gas in collapsed halos dominates the small-scale power masking pressure smoothing effects. We introduce a new statistic, the real-space Lyα flux, F{sub real}, which naturally suppresses dense gas, and is thus robust against the poorly understood physics of galaxy formation, revealing pressure smoothing in the diffuse IGM. The F{sub real} power spectrum is accurately described by a simple fitting function with cutoff at λ{sub F}, allowing us to rigorously quantify the pressure smoothing scale for the first time: we find λ{sub F} = 79 kpc (comoving) at z = 3 for our fiducial thermal model. This statistic has the added advantage that it directly relates to observations of correlated Lyα forest absorption in close quasar pairs, recently proposed as a method to measure the pressure smoothing scale. Our results enable one to quantify the pressure smoothing scale in simulations, and ask meaningful questions about its dependence on reionization and thermal history. Accordingly, the standard description of the IGM in terms of the amplitude T{sub 0} and slope γ of the temperature–density relation T=T{sub 0}(ρ/ ρ-bar ){sup γ−1} should be augmented with a third pressure smoothing scale parameter λ{sub F}.},
doi = {10.1088/0004-637X/812/1/30},
url = {https://www.osti.gov/biblio/22882501}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 812,
place = {United Kingdom},
year = {2015},
month = {10}
}