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Title: The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshiftz≈ 0.4–1. Through spectrally resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small aslcl∼ 1 pc and density lower thannH= 10−3cm−3are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperatureTand the nonthermal motionsbNT, independent of the ionization models. On average,bNTis found to increase withlclfollowingbNTlcl0.3over three decades in spatial scale fromlcl≈ 1 pc tolcl≈ 1 kpc. Attributing the observedbNTto turbulent motions internal to the clumps, the best-fitbNTlclrelation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass ofϵ≈ 0.003 cm2s−3and a dissipation timescale of ≲100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferredϵis comparable to what is found in Civabsorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

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DOI PREFIX: 10.3847
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Journal Name:
The Astrophysical Journal Letters
Medium: X Size: Article No. L25
["Article No. L25"]
Sponsoring Org:
National Science Foundation
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