An origin for multiphase gas in galactic winds and haloes

By T. Thompson, E. Quataert, Dong Zhang, D. Weinberg. 2015

170 citations recorded by the source corpus.

The physical origin of high velocity cool gas seen in galactic winds remains unknown. Following Wang (1995), we argue that radiative cooling in initially hot thermally-driven outflows can produce fast neutral atomic and photoionized cool gas. The inevitability of adiabatic cooling from the flow's initial 10^7-10^8K temperature and the shape of the cooling function for T 0.5 cool radiatively on scales ranging from the size of the energy injection region to tens of kpc. We highlight the beta and star formation rate surface density dependence of the column density, emission measure, radiative efficiency, and velocity. At r_cool, the gas produces X-ray and then UV/optical line emission with a total power bounded by 10^{-2} L_star if the flow is powered by steady-state star formation with luminosity L_star. The wind is thermally unstable at r_cool, potentially leading to a multi-phase medium. Cooled winds decelerate significantly in the extended gravitational potential of galaxies. The cool gas precipitated from hot outflows may explain its prevalence in galactic halos. We forward a picture of winds whereby cool clouds are initially accelerated by the ram pressure of the hot flow, but are rapidly shredded by hydrodynamical instabilities, thereby increasing beta, seeding radiative and thermal instability, and cool gas rebirth. If the cooled wind shocks as it sweeps up the circumgalactic medium, its cooling time is short, thus depositing cool gas far out into the halo. Finally, conduction can dominate energy transport in low-beta hot winds, leading to flatter temperature profiles than otherwise expected, potentially consistent with X-ray observations of some starbursts.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/16d97e012e34397f8c737b455c3cd490fe4cb3cc

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In Astronomy and Astrophysics

1. L. Hernquist
2. Volker Springel
3. P. Hopkins
4. P. Torrey
5. Shy Genel
6. M. Vogelsberger
7. E. Quataert
8. D. Nelson

Citations in the corpus

• Cool outflows in galaxies and their implications (2020, background): “Clouds that start as radiativelydriven experience gentler accelerations, and although they may later be advected in a hot flow and ultimately destroyed, they can potentially reach large distances and high velocities (Thompson et al. 2015).”
• The growth and entrainment of cold gas in a hot wind (2018, background): “Another possibility is the cold gas forming from an adiabatically cooling wind (Thompson et al. 2016; Schneider et al. 2018).”
• A Global Model for Circumgalactic and Cluster-core Precipitation (2016, background): “This simple relationship is likely to be the biggest driver of condensation in more complex treatments of multiphase outflows (e.g., Thompson et al. 2016)”
• The Circumgalactic Medium (2017, background): “…driven by local thermal instabilities (e.g. McCourt et al. 2012); (2) boundary layers between moving cool clouds in a hot atmosphere (e.g. Begelman & Fabian 1990); and (3) the continual shocking and mixing of diffuse halo gas by galactic outflows (e.g. Fielding et al. 2016; Thompson et al. 2016).”
• First results from the TNG50 simulation: galactic outflows driven by supernovae and black hole feedback (2019, background): “= 109 M , together with the invariance of the peak temperature itself in relation to the shape of our adopted cooling curve (Wiersma et al. 2009) suggests a cooling process (possibly in the outflow itself, e.g. Thompson et al. 2016; Schneider et al. 2018).”
• THE COS-HALOS SURVEY: ORIGINS OF THE HIGHLY IONIZED CIRCUMGALACTIC MEDIUM OF STAR-FORMING GALAXIES (2016, background): “Recently, Thompson et al. (2016) presented a detailed picture in which initially hot, adiabatic outflows radiatively cool on large scales (∼ 100 kpc) and timescales less than a Hubble time.”
• A characteristic scale for cold gas (2016, background): “The optically-thick covering fraction is known to evolve rapidly with galaxy mass (cf. Rudie et al. 2012 and Prochaska, Hennawi & Simcoe 2013; Thompson et al. 2016).”
• The impact of star formation feedback on the circumgalactic medium (2016, background): “These small clumps may have formed as result of rapid cooling of galactic wind shocked material (e.g. Thompson et al. 2016), or as a result of pressure confinement after condensing out of a hotter, thermally unstable background (e.g. McCourt et al. 2012, 2016).”