%0 Generic %1 zhang2015entrainment %A Zhang, Dong %A Thompson, Todd A. %A Quataert, Eliot %A Murray, Norman %D 2015 %K clouds entrainment outflows %T Entrainment in Trouble: Cool Cloud Acceleration and Destruction in Hot Supernova-Driven Galactic Winds %U http://arxiv.org/abs/1507.01951 %X Efficient thermalization of overlapping supernovae within star-forming galaxies may produce a supernova-heated fluid that drives galactic winds. For fiducial assumptions about the timescale for Kelvin-Helmholz (KH) instabilities from high-resolution simulations (which neglect magnetic fields) we show that cool clouds with temperature from T_c ~ 10^2-10^4 K seen in emission and absorption in galactic winds cannot be accelerated to observed velocities by the ram pressure of a hot wind. Taking into account both the radial structure of the hot flow and gravity, we show that this conclusion holds over a wide range of galaxy, cloud, and hot wind properties. This finding calls into question the prevailing picture whereby the cool atomic gas seen in galactic winds is entrained and accelerated by the hot flow. Given these difficulties with ram pressure acceleration, we discuss alternative models for the origin of high velocity cool gas outflows. Another possibility is that magnetic fields in cool clouds are sufficiently important that they prolong the cloud's life. For T_c = 10^3 K and 10^4 K clouds, we show that if conductive evaporation can be neglected, the KH timescale must be ~ 10 and 3 times longer, respectively, than the values from hydrodynamical simulations in order for cool cloud velocities to reach those seen in observations.

@misc{zhang2015entrainment, abstract = {Efficient thermalization of overlapping supernovae within star-forming galaxies may produce a supernova-heated fluid that drives galactic winds. For fiducial assumptions about the timescale for Kelvin-Helmholz (KH) instabilities from high-resolution simulations (which neglect magnetic fields) we show that cool clouds with temperature from T_c ~ 10^2-10^4 K seen in emission and absorption in galactic winds cannot be accelerated to observed velocities by the ram pressure of a hot wind. Taking into account both the radial structure of the hot flow and gravity, we show that this conclusion holds over a wide range of galaxy, cloud, and hot wind properties. This finding calls into question the prevailing picture whereby the cool atomic gas seen in galactic winds is entrained and accelerated by the hot flow. Given these difficulties with ram pressure acceleration, we discuss alternative models for the origin of high velocity cool gas outflows. Another possibility is that magnetic fields in cool clouds are sufficiently important that they prolong the cloud's life. For T_c = 10^3 K and 10^4 K clouds, we show that if conductive evaporation can be neglected, the KH timescale must be ~ 10 and 3 times longer, respectively, than the values from hydrodynamical simulations in order for cool cloud velocities to reach those seen in observations.}, added-at = {2015-07-09T09:44:31.000+0200}, author = {Zhang, Dong and Thompson, Todd A. and Quataert, Eliot and Murray, Norman}, biburl = {https://www.bibsonomy.org/bibtex/24ab35122c090a68d92c25ca7d43ecc9a/miki}, description = {[1507.01951] Entrainment in Trouble: Cool Cloud Acceleration and Destruction in Hot Supernova-Driven Galactic Winds}, interhash = {ae02fc85bf6d96f677b1376cc9173fd9}, intrahash = {4ab35122c090a68d92c25ca7d43ecc9a}, keywords = {clouds entrainment outflows}, note = {cite arxiv:1507.01951Comment: 14 pages, 6 figures, 1 table, submitted}, timestamp = {2015-07-09T09:44:31.000+0200}, title = {Entrainment in Trouble: Cool Cloud Acceleration and Destruction in Hot Supernova-Driven Galactic Winds}, url = {http://arxiv.org/abs/1507.01951}, year = 2015 }