The Chevalier & Clegg (1985) spherical wind is widely used to model galactic outflows. Efforts ar... more The Chevalier & Clegg (1985) spherical wind is widely used to model galactic outflows. Efforts are underway to understand the production of multiphase gas in such outflows. Since the important scales for the multiphase gas are very small compared to the size of the wind, it is very useful to have a local model of the cold gas interacting with a volume-filling expanding wind. In this note we explicitly derive the governing hydrodynamic equations in such a local box for the first time. We highlight that the expansion in a wind occurs only in the transverse direction, and this results in anisotropic source terms in the momentum equation. Our equations will be very useful in realistic modelling of the small scale structure of multiphase galactic outflows. [original note does not include an abstract]
Monthly Notices of the Royal Astronomical Society, 2021
Cold, non-self-gravitating clumps occur in various astrophysical systems, ranging from the inters... more Cold, non-self-gravitating clumps occur in various astrophysical systems, ranging from the interstellar and circumgalactic medium (CGM), to active galactic nucleus outflows and solar coronal loops. Cold gas has diverse origins such as turbulent mixing or precipitation from hotter phases. We obtain the analytical solution for a steady pressure-driven 1D cooling flow around cold, local overdensities, irrespective of their origin. Our solutions describe the slow and steady radiative cooling-driven gas inflow in the saturated regime of non-linear thermal instability in clouds, sheets, and filaments. Such a cooling flow develops when the gas around small clumps undergoes radiative cooling. These small-scale, cold ‘seeds’ are embedded in a large volume-filling hot CGM maintained by feedback. We use a simple two-fluid treatment to include magnetic fields as an additional polytropic fluid. To test the limits of applicability of these analytical solutions, we compare with the gas structure f...
Monthly Notices of the Royal Astronomical Society, 2020
We revisit the problem of the growth of dense/cold gas in the cloud-crushing setup with radiative... more We revisit the problem of the growth of dense/cold gas in the cloud-crushing setup with radiative cooling. This model problem captures the interaction of a pre-existing cold cloud with a hot and dilute background medium, through which it moves. The relative motion produces a turbulent boundary layer of mixed gas with a short cooling time. The cooling of this mixed gas in the wake of clouds may explain the ubiquity of a multiphase gas in various sources such as the circumgalactic medium (CGM) and galactic/stellar/AGN outflows. In absence of radiative cooling, the cold gas is mixed in the hot medium before it becomes comoving with it. Recently Gronke & Oh, based on 3D hydrodynamic simulations, showed that with efficient radiative cooling of the mixed gas in the turbulent boundary layer, cold clouds can continuously grow and entrain mass from the diffuse background. They presented an analytic criterion for such growth to happen -- namely, the cooling time of the mixed phase be shorter ...
The Chevalier & Clegg (1985) spherical wind is widely used to model galactic outflows. Efforts ar... more The Chevalier & Clegg (1985) spherical wind is widely used to model galactic outflows. Efforts are underway to understand the production of multiphase gas in such outflows. Since the important scales for the multiphase gas are very small compared to the size of the wind, it is very useful to have a local model of the cold gas interacting with a volume-filling expanding wind. In this note we explicitly derive the governing hydrodynamic equations in such a local box for the first time. We highlight that the expansion in a wind occurs only in the transverse direction, and this results in anisotropic source terms in the momentum equation. Our equations will be very useful in realistic modelling of the small scale structure of multiphase galactic outflows. [original note does not include an abstract]
Monthly Notices of the Royal Astronomical Society, 2021
Cold, non-self-gravitating clumps occur in various astrophysical systems, ranging from the inters... more Cold, non-self-gravitating clumps occur in various astrophysical systems, ranging from the interstellar and circumgalactic medium (CGM), to active galactic nucleus outflows and solar coronal loops. Cold gas has diverse origins such as turbulent mixing or precipitation from hotter phases. We obtain the analytical solution for a steady pressure-driven 1D cooling flow around cold, local overdensities, irrespective of their origin. Our solutions describe the slow and steady radiative cooling-driven gas inflow in the saturated regime of non-linear thermal instability in clouds, sheets, and filaments. Such a cooling flow develops when the gas around small clumps undergoes radiative cooling. These small-scale, cold ‘seeds’ are embedded in a large volume-filling hot CGM maintained by feedback. We use a simple two-fluid treatment to include magnetic fields as an additional polytropic fluid. To test the limits of applicability of these analytical solutions, we compare with the gas structure f...
Monthly Notices of the Royal Astronomical Society, 2020
We revisit the problem of the growth of dense/cold gas in the cloud-crushing setup with radiative... more We revisit the problem of the growth of dense/cold gas in the cloud-crushing setup with radiative cooling. This model problem captures the interaction of a pre-existing cold cloud with a hot and dilute background medium, through which it moves. The relative motion produces a turbulent boundary layer of mixed gas with a short cooling time. The cooling of this mixed gas in the wake of clouds may explain the ubiquity of a multiphase gas in various sources such as the circumgalactic medium (CGM) and galactic/stellar/AGN outflows. In absence of radiative cooling, the cold gas is mixed in the hot medium before it becomes comoving with it. Recently Gronke & Oh, based on 3D hydrodynamic simulations, showed that with efficient radiative cooling of the mixed gas in the turbulent boundary layer, cold clouds can continuously grow and entrain mass from the diffuse background. They presented an analytic criterion for such growth to happen -- namely, the cooling time of the mixed phase be shorter ...
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