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Growth and Evolution of Thermal Instabilities in Idealized Galaxy-Cluster Cores
Cosmology and Nongalactic Astrophysics · Submitted 24 Feb 2015
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio tcool /tff < 10 is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation.
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The abstract, sentence by sentence
Heat input roughly balances radiative cooling in the gaseous cores of galaxy clusters even when the central cooling time is short, implying that cooling triggers a feedback loop that maintains thermal balance. Furthermore, cores with short cooling times tend to have multiphase structure, suggesting that the intracluster medium (ICM) becomes locally thermally unstable for cooling times < 1 Gyr. In this work, we use 2D and 3D hydrodynamic simulations to study the onset of condensation in idealized galaxy-cluster cores. In particular, we look at how the condensation process depends on the ratio of cooling time to freefall time and on the geometry of the gravitational potential. We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio tcool /tff < 10 is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation. We find that instability leads to convection and that perturbations continue to grow while the gas convects. Condensation occurs when the timescale ratio in the low-entropy tail of the perturbation distribution drops below tcool /tff < 3, even if the volume-averaged timescale ratio is substantially greater. In our simulations, the geometry of the gravitational potential does not have a strong effect on thermal stability. Finally, we find that if condensation is powering feedback, a conversion efficiency of around 10^-3 for converting the condensed mass into thermal energy is sufficient to maintain thermal balance in the ICM.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Heat input roughly balances radiative cooling in the gaseous cores of galaxy clusters even when the central cooling time is short, implying that cooling triggers a feedback loop that maintains thermal balance. | background 0.96 | 0.10 | 0.08 | asserted 0.81 |
| s1 | Furthermore, cores with short cooling times tend to have multiphase structure, suggesting that the intracluster medium (ICM) becomes locally thermally unstable for cooling times < 1 Gyr. | background 0.96 | 0.12 | 0.04 | hedged possibility 0.99 |
| s2 | In this work, we use 2D and 3D hydrodynamic simulations to study the onset of condensation in idealized galaxy-cluster cores. | method 0.55 | 0.96 | 0.02 | asserted 0.76 |
| s3 | In particular, we look at how the condensation process depends on the ratio of cooling time to freefall time and on the geometry of the gravitational potential. | method 0.55 | 0.78 | 0.02 | unclear 0.51 |
| s4 | We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio tcool /tff < 10 is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation. | result 0.97 | 0.92 | 0.87 | asserted 0.99 |
| s5 | We find that instability leads to convection and that perturbations continue to grow while the gas convects. | result 1.00 | 0.90 | 0.05 | asserted 1.00 |
| s6 | Condensation occurs when the timescale ratio in the low-entropy tail of the perturbation distribution drops below tcool /tff < 3, even if the volume-averaged timescale ratio is substantially greater. | result 1.00 | 0.91 | 0.12 | asserted 1.00 |
| s7 | In our simulations, the geometry of the gravitational potential does not have a strong effect on thermal stability. | result 1.00 | 0.95 | 0.04 | asserted 1.00 |
| s8 | Finally, we find that if condensation is powering feedback, a conversion efficiency of around 10^-3 for converting the condensed mass into thermal energy is sufficient to maintain thermal balance in the ICM. | result 0.92 | 0.94 | 0.12 | asserted 0.98 |
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Original abstract
Heat input roughly balances radiative cooling in the gaseous cores of galaxy clusters even when the central cooling time is short, implying that cooling triggers a feedback loop that maintains thermal balance. Furthermore, cores with short cooling times tend to have multiphase structure, suggesting that the intracluster medium (ICM) becomes locally thermally unstable for cooling times < 1 Gyr. In this work, we use 2D and 3D hydrodynamic simulations to study the onset of condensation in idealized galaxy-cluster cores. In particular, we look at how the condensation process depends on the ratio of cooling time to freefall time and on the geometry of the gravitational potential. We conclude that the ICM can always evolve to a state in which condensation occurs if given enough time, but that an initial timescale ratio tcool /tff < 10 is needed for thermal instability to grow quickly enough to affect realistic cluster cores within a timescale that is relevant for cosmological structure formation. We find that instability leads to convection and that perturbations continue to grow while the gas convects. Condensation occurs when the timescale ratio in the low-entropy tail of the perturbation distribution drops below tcool /tff < 3, even if the volume-averaged timescale ratio is substantially greater. In our simulations, the geometry of the gravitational potential does not have a strong effect on thermal stability. Finally, we find that if condensation is powering feedback, a conversion efficiency of around 10^-3 for converting the condensed mass into thermal energy is sufficient to maintain thermal balance in the ICM.
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References
How the literature uses it
1 arXiv paper cite this in 1 sentence
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When the entropy profile is used to infer a cooling time, [ref] a central entropy of 30 KeV corresponds to a cooling time of around 1 billion years, consistent with a cooling time to freefall time ratio of around 10.
Regulation of star formation in giant galaxies by precipitation, feedback, and conduction · Observations of Multiphase Gas · 0.85
Cites as support 1 paper
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The analysis of [ref] strongly suggests that the latter “cold feedback” mode is more important, because of a universal floor observed in the radial cooling-time profiles of galaxy clusters that corresponds to the predicted threshold for condensation of cold clouds [ref] .
Regulation of star formation in giant galaxies by precipitation, feedback, and conduction · Introduction · 0.99
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