Detection of turbulence in the hot circumgalactic medium (CGM) of the Milky Way

The density of the hot (>10⁶ K) CGM of the Milky Way is often modeled with an underlying assumption of isotropic density distribution. However, the large (>order-of-magnitude) scatter in the column density of the hot CGM, N(H), contradicts that assumption. N(H) is calculated from z=0 absorption lines of OVII and OVIII toward extragalactic (b>20^o) sightlines using X-ray grating spectroscopy and an assumed uniform metallicity, O/H, across the sky. We calculate the structure function, S(θ) ∝ (δn)² from N(H) as a measure of the density fluctuation, δn. We find that S(θ) grows with θ, the angular separation between sightlines, at a power-law slope of 2.21±0.33, consistent with a Kolmogorov-like slope of 5/3 within 2σ. The driving scale of turbulence, beyond which S(θ) saturates, is 60% of the length scale of the hot CGM, indicating large-scale turbulence.