Kinematics of H i and O vi Absorbers: Insights into the Turbulence Driver of the Multiphase Circumgalactic Medium

Abstract We investigate large-scale gas kinematics in the multiphase circumgalactic medium (CGM) using the observed correlation between line width (Doppler b parameter) and column density ( N ) for H i and O vi absorbers. Leveraging extensive public galaxy survey data at z ≲ 0.1, we construct a new galaxy sample based on the availability of background quasi-stellar objects with far-ultraviolet spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE). By combining this FUSE galaxy sample with literature collections, we find that H i absorbers exhibit a clear inverse correlation between Doppler width and column density over nearly 5 orders of magnitude in N HI , from N HI ≈ 10 13 cm −2 to N HI ≈ 10 18 cm −2 , while O vi absorption follows a positive correlation across N OVI ≈ 3 × 10 13 –10 15 cm −2 . We develop a model framework to interpret these contrasting trends and show that H i absorbers are best described as systems of approximately constant total column density ( N H ), whereas O vi traces regions of roughly constant spatial density ( n H and n O VI ). Under the latter scenario, the observed b O VI – N O VI relation maps directly to a velocity–size relation consistent with a Kolmogorov-like turbulent spectrum. Together, these findings reveal a coherent physical picture in which H i and O vi trace a continuous turbulent cascade spanning more than 5 orders of magnitude in spatial scale—from cool, photoionized clumps to warm, highly ionized halo gas—with accretion in the halo outskirts likely driving the turbulent energy injection that sustains the multiphase CGM.