Thermal instabilities and shattering in the high-redshift WHIM: convergence criteria and implications for low-metallicity strong H i absorbers

Mandelker, Nir, van den Bosch, Frank C., Springel, Volker, van de Voort, Freeke ORCID: https://orcid.org/0000-0002-6301-638X, Burchett, Joseph N., Butsky, Iryna S., Nagai, Daisuke and Oh, S. Peng 2021. Thermal instabilities and shattering in the high-redshift WHIM: convergence criteria and implications for low-metallicity strong H i absorbers. Astrophysical Journal 923 (1) , 115. 10.3847/1538-4357/ac2d29

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Abstract

Using a novel suite of cosmological simulations zooming in on a megaparsec-scale intergalactic sheet (pancake) at z ∼ (3–5), we conduct an in-depth study of the thermal properties and H i content of the warm-hot intergalactic medium (WHIM) at those redshifts. The simulations span nearly three orders of magnitude in gas cell mass, ∼(7.7 × 106–1.5 × 104)M⊙, one of the highest-resolution simulations of such a large patch of the intergalactic medium (IGM) to date. At z ∼ 5, a strong accretion shock develops around the pancake. Gas in the postshock region proceeds to cool rapidly, triggering thermal instabilities and generating a multiphase medium. We find the mass, morphology, and distribution of H i in the WHIM to all be unconverged, even at our highest resolution. Interestingly, the lack of convergence is more severe for the less-dense, metal-poor intrapancake medium (IPM) in between filaments and far outside galaxies. With increased resolution, the IPM develops a shattered structure with most of the H i in kiloparsec-scale clouds. From our lowest-to-highest resolution, the covering fraction of metal-poor (Z < 10−3Z⊙) Lyman-limit systems (NH I > 1017.2cm−2) in the z ∼ 4 IPM increases from ∼(3–15)%, while that of metal-poor damped Lyα absorbers (NH I > 1020cm−2) increases from ∼(0.2–0.6)%, with no sign of convergence. We find that a necessary condition for the formation of a multiphase shattered structure is resolving the cooling length, lcool = cstcool, at T ∼ 105 K. If this is unresolved, gas "piles up" at T ≲ 105 K and further cooling becomes very inefficient. We conclude that state-of-the-art cosmological simulations are still unable to resolve the multiphase structure of the WHIM, with potentially far-reaching implications.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Astronomical Society
ISSN:	0004-637X
Date of First Compliant Deposit:	9 March 2022
Date of Acceptance:	4 October 2021
Last Modified:	23 Nov 2023 07:18
URI:	https://orca.cardiff.ac.uk/id/eprint/148170

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