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Description
We develop a kinematical model for the Milky Way SiIV-bearing gas to determine its density distribution and kinematics. This model is constrained by a column density line-shape sample extracted from the Hubble Space Telescope/Cosmic Origins Spectrograph archival data, which contains 186 active galactic nucleus sight lines. We find that the SiIV ion density distribution is dominated by an extended disk along the z-direction (above or below the midplane), i.e., n(z)=n_0_exp(-(z/z_0_)^0.82^), where z_0_ is the scale height of 6.3_-1.5_^+1.6^kpc (northern hemisphere) and 3.6_-0.9_^+1.0^kpc (southern hemisphere). The density distribution of the disk in the radial direction shows a sharp edge at 15-20kpc given by, n(r_XY_)=n_0_exp(-(r_XY_/r_0_)^3.36^), where r_0_~12.5+/-0.6kpc. The difference of density distributions over r_XY_ and z directions indicates that the warm gas traced by SiIV is mainly associated with disk processes (e.g., feedback or cycling gas) rather than accretion. We estimate the mass of the warm gas (within 50kpc) is log(M(50kpc)/M_{sun}_)~8.1 (assuming Z~0.5Z_{sun}_), and a 3{sigma} upper limit of log(M(250kpc)/M_{sun}_)~9.1 (excluding the Magellanic system). Kinematically, the warm gas disk is nearly co-rotating with the stellar disk at v_rot_=215+/-3km/s, which lags the midplane rotation by about 8km/s/kpc (within 5kpc). Meanwhile, we note that the warm gas in the northern hemisphere has significant accretion with vacc of 69+/-7km/s at 10kpc (an accretion rate of -0.60_-0.13_^+0.11^M_{sun}_/yr), while in the southern hemisphere, there is no measurable accretion, with an upper limit of 0.4M_{sun}_/yr.
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