Thermal Instabilities and Shattering in the High-redshift WHIM: Convergence Criteria and Implications for Low-metallicity Strong H I Absorbers
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 < 10-3 Z ⊙) Lyman-limit systems (N H I > 1017.2cm-2) in the z ~ 4 IPM increases from ~(3-15)%, while that of metal-poor damped Lyα absorbers (N H 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, l cool = c s t cool, 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.
- Publication:
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The Astrophysical Journal
- Pub Date:
- December 2021
- DOI:
- 10.3847/1538-4357/ac2d29
- arXiv:
- arXiv:2107.03395
- Bibcode:
- 2021ApJ...923..115M
- Keywords:
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- 343;
- 902;
- 813;
- 1966;
- 811;
- 1317;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 24 pages, 15 (rather large) figures, 2 tables, 1 appendix (main body 21 pages) Comments welcome! Main observational results in sections 3-4 (Table 2) Main theory result in section 6.1