Milky Way SiIV and CIV kinematics from HST/COS

CIV has a higher ionization potential (47-64eV) than SiIV (33-45eV), so it also traces warm gas, which is roughly cospatial with SiIV. The spatial density distribution and kinematics of CIV are identical to those SiIV within ~2{sigma}.

CIV is more sensitive to the warm gas density distribution at large radii with a higher element abundance. Applying the kinematical model to the CIV sample, we find two possible solutions of the density distribution, which are distinguished by the relative extension along the disk midplane and the normal-line direction. Both solutions can reproduce the existing sample and suggest a warm gas disk mass of logM(M_{sun}_)~8 and an upper limit of logM(M_{sun}_)<9.3 within 250kpc, which is consistent with SiIV.