Implications of the large OVI columns around low-redshift $L_\star$ galaxies

摘要: Observations reveal massive amounts of OVI around star-forming $L_*$ galaxies, with covering fractions near unity extending to the host halo's virial radius. This absorption is typically kinematically centered upon photoionized gas, line widths that are suprathermal and offset from galaxy. We discuss various scenarios whether they could result in observed phenomenology (cooling gas flows, boundary layers, shocks, virialized clouds thermal equilibrium). If predominantly collisionally ionized, as we argue most probable, observations require circumgalactic medium (CGM) galaxies holds nearly all associated baryons within a radius ($\sim 10^{11}M_\odot$) hosts flows cooling $\approx30[nT/30{\rm~cm^{-3}K}]~M_\odot~$yr$^{-1}$, which must be largely prevented accreting onto Cooling feedback energetics considerations $10 <\langle nT\rangle<100{\rm~cm^{-3}K}$ for warm hot halo gases. winds, shocks unlikely directly account bulk OVI. Furthermore, show there robust constraint on number density many $\sim10^4$K systems yields upper bounds range $n<(0.1-3)\times10^{-3}(Z/0.3)$cm$^{-3}$, where $Z$ metallicity, suggestive dominant pressure some nonthermal. constraint, requires minimal ionization modeling, accord low densities inferred more complex photoionization modeling. The large amount re-form these fraction dynamical time, arguments require, it much energy available supernovae stellar winds dissipated CGM.