Resolving small-scale cold circumgalactic gas in TNG50
ABSTRACT We use the high-resolution TNG50 cosmological magnetohydrodynamical simulation to explore the properties and origin of cold circumgalactic medium (CGM) gas around massive galaxies (M⋆ > 1011 M⊙ ) at intermediate redshift ($z \sim 0.5$). We discover a significant abundance of small-scale,...
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Published in | Monthly notices of the Royal Astronomical Society Vol. 498; no. 2; pp. 2391 - 2414 |
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Main Authors | , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Oxford University Press
01.10.2020
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Subjects | |
Online Access | Get full text |
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Summary: | ABSTRACT
We use the high-resolution TNG50 cosmological magnetohydrodynamical simulation to explore the properties and origin of cold circumgalactic medium (CGM) gas around massive galaxies (M⋆ > 1011 M⊙ ) at intermediate redshift ($z \sim 0.5$). We discover a significant abundance of small-scale, cold gas structure in the CGM of ‘red and dead’ elliptical systems, as traced by neutral H i and Mg ii. Halos can host tens of thousands of discrete absorbing cloudlets, with sizes of order a kpc or smaller. With a Lagrangian tracer analysis, we show that cold clouds form due to strong $\delta \rho / \bar{\rho } \gg 1$ gas density perturbations that stimulate thermal instability. These local overdensities trigger rapid cooling from the hot virialized background medium at ∼107 K to radiatively inefficient ∼104 K clouds, which act as cosmologically long-lived, ‘stimulated cooling’ seeds in a regime where the global halo does not satisfy the classic tcool/tff < 10 criterion. Furthermore, these small clouds are dominated by magnetic rather than thermal pressure, with plasma β ≪ 1, suggesting that magnetic fields may play an important role. The number and total mass of cold clouds both increase with resolution, and the mgas ≃ 8 × 104 M⊙ cell mass of TNG50 enables the ∼ few hundred pc, small-scale CGM structure we observe to form. Finally, we make a preliminary comparison against observations from the COS-LRG, LRG-RDR, COS-Halos, and SDSS LRG surveys. We broadly find that our recent, high-resolution cosmological simulations produce sufficiently high covering fractions of extended, cold gas as observed to surround massive galaxies. |
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ISSN: | 0035-8711 1365-2966 |
DOI: | 10.1093/mnras/staa2419 |