While most ram pressure studies have focused on ram pressure stripping ingalaxy clusters, we devise a novel approach based on a kinematic measurement ofram pressure perturbations in HI velocity fields for intergalactic material(IGM) densities and relative velocities that are one to two orders of magnitudelower than in galaxies showing ram pressure stripping. Our model evaluates rampressure induced kinematic terms in gas disks with constant inclination as wellas those with a warped geometry. Ram pressure perturbations are characterizedby kinematic modes of even order, m=0 and m=2, corresponding to a ram windperpendicular and parallel to the gas disk, respectively. Long-termconsequences of ram pressure, such as warped disks as well as uncertainties inthe disk geometry typically generate uneven modes (m=1 and m=3), that areclearly distinguishable from the kinematic ram pressure terms. We have appliedour models to three nearby isolated galaxies, utilizing Markov Chain MonteCarlo fitting routines to determine ram pressure perturbations in the velocityfields of NGC 6946 and NGC 3621 of ~30km s$^{-1}$ (effective line-of-sightvelocity change) at HI column densities below (4-10)$\times$10$^{20}$cm$^{-2}$(at radial scales greater than ~15kpc). In contrast, NGC 628 is dominated by astrongly warped disk. Our model fits reveal the three-dimensional vector of thegalaxies' movement with respect to the IGM rest-frame and provide constraintson the product of speed with IGM density, opening a new window forextragalactic velocity measurements and studies of the intergalactic medium.
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