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 $z\lesssim0.1$, we construct a new galaxy sample based on the availability of background Quasi-Stellar Objects (QSOs) 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 five orders of magnitude in $N_{\rm HI}$, from $N_{\rm HI} \approx 10^{13}\,\mathrm{cm^{-2}}$ to $N_{\rm HI} \approx 10^{18}\,\mathrm{cm^{-2}}$, while O VI absorption follows a positive correlation across $N_{\rm OVI}\approx 3\times10^{13}$-$10^{15}\,\mathrm{cm^{-2}}$.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 ($N_{\rm H}$), whereas O VI traces regions of roughly constant spatial density ($n_{\rm H}$ and $n_{\rm OVI}$). Under the latter scenario, the observed $b_{\rm OVI}$-$N_{\rm OVI}$ 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 five 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.