Recent years have seen excellent progress in modelling the entrainment of T ∼ 104 K atomic gas in galactic winds. However, the entrainment of cool, dusty T ∼ 10–100 K molecular gas, which is also observed outflowing at high velocity, is much less understood. Such gas, which can be 105 times denser than the hot wind, appears extremely difficult to entrain. We run 3D wind-tunnel simulations with photoionization self-shielding and evolve thermal dust sputtering and growth. Unlike almost all such simulations to date, we do not enforce any artificial temperature floor. We find efficient molecular gas formation and entrainment, as well as dust survival and growth through accretion. Key to this success is the formation of large amounts of 104 K atomic gas via mixing, which acts as a protective ‘bubble wrap’ and reduces the cloud overdensity to χ ∼ 100. This can be understood from the ratio of the mixing to cooling time. Before entrainment, when shear is large, tmix/tcool ≲ 1, and gas cannot cool below the ‘cooling bottleneck’ at 5000 K. Thus, the cloud survival criterion is identical to the well-studied purely atomic case. After entrainment, when shear falls, tmix/tcool > 1, and the cloud becomes multiphase, with comparable molecular and atomic masses. The broad temperature PDF, with abundant gas in the formally unstable $50 \, {\rm K} \lt T \lt 5000 \, {\rm K}$ range, agrees with previous ISM simulations with driven turbulence and radiative cooling. Our findings have implications for dusty molecular gas in stellar and active galactic nuclei outflows, cluster filaments, ‘jellyfish’ galaxies, and asymptomatic giant branch winds.
Much progress has been made recently in the acceleration of ∼104 K clouds to explain absorption line measurements of the circumgalactic medium and the warm, atomic phase of galactic winds. However, the origin of the cold, molecular phase in galactic winds has received relatively little theoretical attention. Studies of the survival of ∼104 K clouds suggest efficient radiative cooling may enable the survival of expelled material from galactic discs. Alternatively, gas colder than 104 K may form within the outflow, including molecules if dust survives the acceleration process. We explore the survival of dusty clouds in a hot wind with three-dimensional hydrodynamic simulations including radiative cooling and dust modelled as tracer particles. We find that cold ∼103 K gas can be destroyed, survive, or transformed entirely to ${\sim}10^4\,$ K gas. We establish analytic criteria distinguishing these three outcomes that compare characteristic cooling times to the system’s ‘cloud crushing’ time. In contrast to typically studied ∼104 K clouds, colder clouds are entrained faster than the drag time as a result of efficient mixing. We find that while dust can in principle survive embedded in the accelerated clouds, the survival fraction depends critically on the time dust spends in the hot phase and on the effective threshold temperature for destruction. We discuss our results in the context of polluting the circumgalactic medium with dust and metals, as well as understanding observations suggesting rapid acceleration of molecular galactic winds and ram-pressure-stripped tails of jellyfish galaxies.
more » « less- NSF-PAR ID:
- 10360878
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 510
- Issue:
- 1
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 551-567
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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