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 $z\lesssim 0.1$, 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 $N_{\mathrm{HI}}$, from $N_{\mathrm{HI}}\approx 10^{13}\mathrm{c}{\mathrm{m}}^{-2}$ to $N_{\mathrm{HI}}\approx 10^{18}\mathrm{c}{\mathrm{m}}^{-2}$, while O VI absorption follows a positive correlation across $N_{\mathrm{OVI}}\approx 3\times 10^{13}$-$10^{15}\mathrm{c}{\mathrm{m}}^{-2}$.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 ($N_{\mathrm{H}}$), whereas O VI traces regions of roughly constant spatial density ($n_{\mathrm{H}}$ and $n_{\mathrm{OVI}}$). Under the latter scenario, the observed $b_{\mathrm{OVI}}$-$N_{\mathrm{OVI}}$ 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.

13 pages, 4 figures, 3 Tables. Accepted to ApJL