Thursday, June 20, 2013

1306.4362 (Mahavir Sharma et al.)

Interaction of galactic wind with halo gas and the origin of multiphase extraplanar material    [PDF]

Mahavir Sharma, Biman B. Nath, Indranil Chattopadhyay, Yuri Shchekinov
We study the interaction of galactic wind with hot halo gas with hydrodynamical simulation. We find that the outcome of this interaction depends crucially on the wind injection density and velocity. If the cooling time of the gas in the interaction zone between the wind and halo gas exceeds the dynamical time of the wind, then a significant amount of warm-hot gas is produced in the interaction zone, which we identify as warm circum-galactic medium (CGM) that can be detected through OVI absorption. If the cooling time is shorter, then the gas in interaction zone fragments into cold clouds. The clouds which form on the side walls of the wind cone, arising from eddies formed due to relative motion between the wind and halo gas, and can resemble high velocity clouds (HVCs). For high injection speed and density, the clouds formed in the thin shell on top of the wind are driven by ram pressure of the steady wind and represent the case of cold/warm clouds observed to be embedded in galactic outflows. We therefore find that the interaction between wind and halo gas can explain the occurrence of a variety of phenomena ranging from HVCs, outflowing clouds and warm CGM, depending on the combination of wind injection speed and density. We show the different regimes in the parameter space of wind speed and density, and discuss the implications in the context of star formation rates of galaxies.
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