%0 Generic %1 citeulike:14138847 %A Cornuault, Nicolas %A Lehnert, Matthew %A Boulanger, Francois %A Guillard, Pierre %D 2016 %K imported %T Are Cosmological Gas Accretion Streams Multiphase and Turbulent? %U http://arxiv.org/abs/1609.04405 %X Simulations of cosmological filamentary accretion streams into galactic halos reveal that such flows are warm at T\$\sim\$10\$^4\$K, laminar, and provide high gas accretion efficiency onto galaxies. We present a phenomenological scenario which suggests that accretion flows are shocked, become thermally unstable, biphasic, and are, as a result, turbulent. We consider a collimated stream of warm gas over denser than the hot, virialized halo gas. The post-shock streaming gas has a higher pressure than the ambient halo gas, expands, and is thermally unstable and fragments, forming a two phase medium -- a hot phase with an embedded warm cloudy phase. The thermodynamic evolution of the post-shock gas is largely determined by the relative timescales of several processes, namely the cooling, the expansion of the hot phase and turbulent warm clouds, and the amount of turbulence in clouds, and the halo dynamics. The cooling is moderated by mixing with the ambient halo gas and heating due to turbulent dissipation. We consider the evolution of a stream for a single halo mass, 10\$^13\$ M\$\_ødot\$, and redshift, 2. We find that the gas becomes thermally unstable and fragments into a two-phase medium where the cooler phase is highly turbulent and has a lower bulk velocity than the initial stream. The turbulent stream loses coherence in less than a halo dynamical time. Both the phase separation and "disruption" of the stream imply that the accretion efficiency onto a galaxy in a dynamical time may be less than in simulations having laminar isothermal flows. De-collimating flows make the direct interaction between galaxy feedback and accretion streams more likely, thereby further reducing the overall accretion efficiency. Moderating the gas accretion efficiency through these mechanisms may help to alleviate a number of significant challenges in theoretical galaxy formation. abridged

@misc{citeulike:14138847, abstract = {Simulations of cosmological filamentary accretion streams into galactic halos reveal that such flows are warm at T\$\sim\$10\$^4\$K, laminar, and provide high gas accretion efficiency onto galaxies. We present a phenomenological scenario which suggests that accretion flows are shocked, become thermally unstable, biphasic, and are, as a result, turbulent. We consider a collimated stream of warm gas over denser than the hot, virialized halo gas. The post-shock streaming gas has a higher pressure than the ambient halo gas, expands, and is thermally unstable and fragments, forming a two phase medium -- a hot phase with an embedded warm cloudy phase. The thermodynamic evolution of the post-shock gas is largely determined by the relative timescales of several processes, namely the cooling, the expansion of the hot phase and turbulent warm clouds, and the amount of turbulence in clouds, and the halo dynamics. The cooling is moderated by mixing with the ambient halo gas and heating due to turbulent dissipation. We consider the evolution of a stream for a single halo mass, 10\$^{13}\$ M\$\_{\odot}\$, and redshift, 2. We find that the gas becomes thermally unstable and fragments into a two-phase medium where the cooler phase is highly turbulent and has a lower bulk velocity than the initial stream. The turbulent stream loses coherence in less than a halo dynamical time. Both the phase separation and "disruption" of the stream imply that the accretion efficiency onto a galaxy in a dynamical time may be less than in simulations having laminar isothermal flows. De-collimating flows make the direct interaction between galaxy feedback and accretion streams more likely, thereby further reducing the overall accretion efficiency. Moderating the gas accretion efficiency through these mechanisms may help to alleviate a number of significant challenges in theoretical galaxy formation. [abridged]}, added-at = {2019-03-25T08:20:55.000+0100}, archiveprefix = {arXiv}, author = {Cornuault, Nicolas and Lehnert, Matthew and Boulanger, Fran\c{c}ois and Guillard, Pierre}, biburl = {https://www.bibsonomy.org/bibtex/24627e4f5454b89300ee8cb468102e5f9/ericblackman}, citeulike-article-id = {14138847}, citeulike-linkout-0 = {http://arxiv.org/abs/1609.04405}, citeulike-linkout-1 = {http://arxiv.org/pdf/1609.04405}, day = 14, eprint = {1609.04405}, interhash = {fea2a7db670e67b9f1afa4ca49389769}, intrahash = {4627e4f5454b89300ee8cb468102e5f9}, keywords = {imported}, month = sep, posted-at = {2016-09-16 16:11:40}, priority = {2}, timestamp = {2019-03-25T08:20:55.000+0100}, title = {{Are Cosmological Gas Accretion Streams Multiphase and Turbulent?}}, url = {http://arxiv.org/abs/1609.04405}, year = 2016 }