%0 Generic %1 thompson2015origin %A Thompson, Todd A. %A Quataert, Eliot %A Zhang, Dong %A Weinberg, David %D 2015 %K galactic gas halo multiphase %T An Origin for Multi-Phase Gas in Galactic Winds and Halos %U http://arxiv.org/abs/1507.04362 %X The origin of high velocity cool gas seen in galactic winds remains unknown. Following Wang (1995), we argue that rapid radiative cooling in initially hot (10^7-10^8 K) thermally-driven outflows can produce fast neutral atomic and photoionized cool gas. Outflows with hot gas mass-loading factor relative to star formation rate of beta > 0.5 cool on scales ranging from the size of the host to tens of kpc. We provide scalings for the cooling radius r_cool, density, column density, emission measure, radiative efficiency, and cool gas velocity. At r_cool, the gas produces X-ray and then UV/optical line emission at velocities of hundreds to thousands of km/s with a total power bounded from above by the energy injection rate 0.01 L_star if the flow is powered by steady-state star formation with luminosity L_star. The wind is thermally and convectively unstable at and beyond r_cool. Thermal instability can amplify density fluctuations by a factor of ~100, potentially leading to a multi-phase medium. Cooled winds can decelerate in the extended gravitational potential of galaxies and may explain the prevalence of cool gas in galactic halos. We forward a picture of winds whereby cool clouds are initially accelerated from the host by ram pressure of the hot flow, but are rapidly shredded and incorporated into the hot flow by the Kelvin-Helmholtz instability. This increases the hot wind mass loading, seeding radiative and thermal instability and cool gas rebirth. We show that if the cooled wind re-shocks as it sweeps up the circumgalactic medium that its cooling time is short, thus depositing cool gas far out into the halo. Finally, we show that conduction can dominate energy transport in low-beta hot galactic winds, leading to much flatter temperature profiles compared to the nominal expectation from adiabaticity, potentially consistent with X-ray observations of some local starbursts. (Abridged)

@misc{thompson2015origin, abstract = {The origin of high velocity cool gas seen in galactic winds remains unknown. Following Wang (1995), we argue that rapid radiative cooling in initially hot (10^7-10^8 K) thermally-driven outflows can produce fast neutral atomic and photoionized cool gas. Outflows with hot gas mass-loading factor relative to star formation rate of beta > 0.5 cool on scales ranging from the size of the host to tens of kpc. We provide scalings for the cooling radius r_cool, density, column density, emission measure, radiative efficiency, and cool gas velocity. At r_cool, the gas produces X-ray and then UV/optical line emission at velocities of hundreds to thousands of km/s with a total power bounded from above by the energy injection rate 0.01 L_star if the flow is powered by steady-state star formation with luminosity L_star. The wind is thermally and convectively unstable at and beyond r_cool. Thermal instability can amplify density fluctuations by a factor of ~100, potentially leading to a multi-phase medium. Cooled winds can decelerate in the extended gravitational potential of galaxies and may explain the prevalence of cool gas in galactic halos. We forward a picture of winds whereby cool clouds are initially accelerated from the host by ram pressure of the hot flow, but are rapidly shredded and incorporated into the hot flow by the Kelvin-Helmholtz instability. This increases the hot wind mass loading, seeding radiative and thermal instability and cool gas rebirth. We show that if the cooled wind re-shocks as it sweeps up the circumgalactic medium that its cooling time is short, thus depositing cool gas far out into the halo. Finally, we show that conduction can dominate energy transport in low-beta hot galactic winds, leading to much flatter temperature profiles compared to the nominal expectation from adiabaticity, potentially consistent with X-ray observations of some local starbursts. (Abridged)}, added-at = {2015-07-17T09:52:08.000+0200}, author = {Thompson, Todd A. and Quataert, Eliot and Zhang, Dong and Weinberg, David}, biburl = {https://www.bibsonomy.org/bibtex/204d105eedf8b5253f186282662d0e7ff/miki}, description = {[1507.04362] An Origin for Multi-Phase Gas in Galactic Winds and Halos}, interhash = {11aa11c58dfd5968132f572d5f72e39b}, intrahash = {04d105eedf8b5253f186282662d0e7ff}, keywords = {galactic gas halo multiphase}, note = {cite arxiv:1507.04362Comment: 15 pages, 5 figures, submitted. Comments welcome}, timestamp = {2015-07-17T09:52:08.000+0200}, title = {An Origin for Multi-Phase Gas in Galactic Winds and Halos}, url = {http://arxiv.org/abs/1507.04362}, year = 2015 }