A comparison of shock–cloud and wind–cloud interactions: effect of increased cloud density contrast on cloud evolution

Abstract

The similarities, or otherwise, of a shock or wind interacting with a cloud of density contrast χ = 10 were explored in a previous paper. Here, we investigate such interactions with clouds of higher density contrast. We compare the adiabatic hydrodynamic interaction of a Mach 10 shock with a spherical cloud of χ = 10 3 with that of a cloud embedded in a wind with identical parameters to the post-shock flow. We find that initially there are only minor morphological differences between the shock-cloud and wind-cloud interactions, compared to when χ = 10. However, once the transmitted shock exits the cloud, the development of a turbulent wake and fragmentation of the cloud differs between the two simulations. On increasing the wind Mach number we note the development of a thin, smooth tail of cloud material, which is then disrupted by the fragmentation of the cloud core and subsequent "mass-loading" of the flow. We find that the normalised cloud mixing time (t mix ) is shorter at higher χ. However, a strong Mach number dependence on t mix and the normalised cloud drag time, t drag , is not observed. Mach-number-dependent values of t mix and t drag from comparable shock-cloud interactions converge towards the Mach-number-independent time-scales of the wind-cloud simulations. We find that high χ clouds can be accelerated up to 80 − 90% of the wind velocity and travel large distances before being significantly mixed. However, complete mixing is not achieved in our simulations and at late times the flow remains perturbed.

Charge-exchange emission and cold clumps in multiphase galactic outflows

“…The Hα filaments are not the CX line emitters. They are trails of gas torn off from neutral clumps by the fast flowing gas around them (see simulations of Suchkov et al 1994;Cooper et al 2008Cooper et al , 2009Scannapieco & Brüggen 2015;Banda-Barragán et al 2016;Brüggen & Scannapieco 2016;Banda-Barragán et al 2018;Goldsmith & Pittard 2018). The stripped material from the cooler CX emitting clumps, when warmed appropriately, emits Hα lines and appears as Hα filaments.…”

Shock-multicloud interactions in galactic outflows -- II. Radiative fractal clouds and cold gas thermodynamics

“…Adiabatic simulations of wind-cloud and shock-cloud interactions have shown that the hotter environment can very effectively remove material from the clouds, heat up their gas, and destroy them via dynamical instabilities (e.g., see Klein, McKee & Colella 1994;Xu & Stone 1995;Nakamura et al 2006;Banda-Barragán et al 2016;Pittard & Parkin 2016;Goldsmith & Pittard 2018). On the other hand, simulations that include the effect of radiative cooling have shown that the lifetime of clouds can be prolonged when cooling is efficient (e.g., see Mellema, Kurk & Röttgering 2002;Cooper et al 2009;Scannapieco & Brüggen 2015;Grønnow et al 2018;Sparre, Pfrommer & Vogelsberger 2019).…”

Dust in RCW 58: clues to common envelope channel formation?

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