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

   https://doi.org/10.3847/2041-8213/acf85b  

   Chen, Hsiao-Wen ; Qu, Zhijie ; Rauch, Michael ; Chen, Mandy C. ; Zahedy, Fakhri S. ; Johnson, Sean D. ; Schaye, Joop ; Rudie, Gwen C. ; Boettcher, Erin ; Cantalupo, Sebastiano ; et al ( September 2023 , The Astrophysical Journal Letters)

   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 asl_cl∼ 1 pc and density lower thann_H= 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 motionsb_NT, independent of the ionization models. On average,b_NTis found to increase withl_clfollowing$b_{\mathrm{NT}}\propto l_{\mathrm{cl}}^{0.3}$over three decades in spatial scale froml_cl≈ 1 pc tol_cl≈ 1 kpc. Attributing the observedb_NTto turbulent motions internal to the clumps, the best-fitb_NT–l_clrelation 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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2. Constraining the Temperature-density Relation of the Inter-galactic Medium from Analytically Modeling Lyα Forest Absorbers

   https://doi.org/10.1088/1674-4527/acbe96  

   Yang, Li ; Zheng, Zheng ; Kim, T.-S. ( March 2023 , Research in Astronomy and Astrophysics)

   Abstract The absorption by neutral hydrogen in the intergalactic medium (IGM) produces the Ly α forest in the spectra of quasars. The Ly α forest absorbers have a broad distribution of neutral hydrogen column density N H I and Doppler b parameter. The narrowest Ly α absorption lines (of lowest b ) with neutral hydrogen column density above ∼10 13 cm −2 are dominated by thermal broadening, which can be used to constrain the thermal state of the IGM. Here we constrain the temperature-density relation T = T 0 ( ρ / ρ ¯ ) γ − 1 of the IGM at 1.6 < z < 3.6 by using N H I and b parameters measured from 24 high-resolution and high-signal-to-noise quasar spectra and by employing an analytic model to model the N H I -dependent low- b cutoff in the b distribution. In each N H I bin, the b cutoff is estimated using two methods, one non-parametric method from computing the cumulative b distribution and a parametric method from fitting the full b distribution. We find that the IGM temperature T 0 at the mean gas density ρ ¯ shows a peak of ∼1.5 × 10 4 K at z ∼ 2.7–2.9. At redshift higher than this, the index γ approximately remains constant, and it starts to increase toward lower redshifts. The evolution in both parameters is in good agreement with constraints from completely different approaches, which signals that He ii reionization completes around z ∼ 3. 

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3. Pressure–Strain Interaction as the Energy Dissipation Estimate in Collisionless Plasma

   https://doi.org/10.3847/1538-4357/ac5d3e  

   Yang 杨, Yan 艳. ; Matthaeus, William H. ; Roy, Sohom ; Roytershteyn, Vadim ; Parashar, Tulasi N. ; Bandyopadhyay, Riddhi ; Wan 万, Minping 敏平 ( April 2022 , The Astrophysical Journal)

   The dissipative mechanism in weakly collisional plasma is a topic that pervades decades of studies without a consensus solution. We compare several energy dissipation estimates based on energy transfer processes in plasma turbulence and provide justification for the pressure–strain interaction as a direct estimate of the energy dissipation rate. The global and scale-by-scale energy balances are examined in 2.5D and 3D kinetic simulations. We show that the global internal energy increase and the temperature enhancement of each species are directly tracked by the pressure–strain interaction. The incompressive part of the pressure–strain interaction dominates over its compressive part in all simulations considered. The scale-by-scale energy balance is quantified by scale filtered Vlasov–Maxwell equations, a kinetic plasma approach, and the lag dependent von Kármán–Howarth equation, an approach based on fluid models. We find that the energy balance is exactly satisfied across all scales, but the lack of a well-defined inertial range influences the distribution of the energy budget among different terms in the inertial range. Therefore, the widespread use of the Yaglom relation in estimating the dissipation rate is questionable in some cases, especially when the scale separation in the system is not clearly defined. In contrast, the pressure–strain interaction balances exactly the dissipation rate at kinetic scales regardless of the scale separation.

    

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4. Thermoelastic Properties of Eclogitic Garnets and Omphacites: Implications for Deep Subduction of Oceanic Crust and Density Anomalies in the Upper Mantle

   https://doi.org/10.1029/2018GL081170  

   Xu, Jingui ; Zhang, Dongzhou ; Fan, Dawei ; Dera, Przemyslaw K. ; Shi, Feng ; Zhou, Wenge ( January 2019 , Geophysical Research Letters)

   Synchrotron‐based high‐pressure/high‐temperature single‐crystal X‐ray diffraction experiments to ~24 GPa and 700 K were conducted on eclogitic garnets (low‐Fe: Prp₂₈Alm₃₈Grs₃₃Sps₁and high‐Fe: Prp₁₄Alm₆₂Grs₁₉Adr₃Sps₂) and omphacites (low‐Fe: Quad₅₇Jd₄₂Ae₁and high‐Fe: Quad₅₃Jd₂₇Ae₂₀), using an externally heated diamond anvil cell. Fitting the pressure‐volume‐temperature data to a third‐order Birch‐Murnaghan equation of state yields the thermoelastic parameters including bulk modulus (K_T0), its pressure derivative (K′_T0), temperature derivative ((∂K_T/∂T)_P), and thermal expansion coefficient (α_T). The densities of the high‐Fe and low‐Fe eclogites were then modeled along typical geotherms of the normal mantle and the subducted oceanic crust to the transition zone depth (550 km). The metastable low‐Fe eclogite could be a reason for the stagnant slabs within the upper range of the transition zone. Eclogite would be responsible for density anomalies within 100–200 km in the upper mantle of Asia.

    

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5. High‐Pressure and High‐Temperature Single‐Crystal Elasticity of Cr‐Pyrope: Implications for the Density and Seismic Velocity of Subcontinental Lithospheric Mantle

   https://doi.org/10.1029/2022GC010393  

   Xu, Jingui ; Fan, Dawei ; Li, Bo ; Tkachev, Sergey N. ; Prakapenka, Vitali B. ; Zhang, Dongzhou ; Yang, Guangzhong ; Zhou, Yi ; Zhou, Wenge ( August 2022 , Geochemistry, Geophysics, Geosystems)

   Single‐crystal X‐ray diffraction and Brillouin spectroscopy experiments were performed on a natural Cr‐pyrope (Prp_71.0Alm_12.6Sps_0.7Grs_3.5Uvr_12.2) at high pressure and high temperature up to 11.0 GPa and 800 K. Fitting the collected data to the third‐order finite strain equation yields bulk modulus (K_S0), shear modulus (G₀), their pressure ((∂K_S/∂P)_Tand (∂G/∂P)_T) and temperature ((∂K_S/∂T)_Pand(∂G/∂T)_P) derivatives,K_S0 = 167.7(8) GPa,G₀ = 91.5(5) GPa, (∂K_S/∂P)_T = 4.3(1), (∂G/∂P)_T = 1.4(1), (∂K_S/∂T)_P = −0.0175(1) GPa/K and (∂G/∂T)_P = −0.0073(1) GPa/K. Using the obtained results, we examined whether the elastic properties of the Cr‐pyrope can be accurately calculated from those of endmembers including pyrope, almandine, grossular, and uvarovite assuming a linear relationship between elastic properties and composition (end‐member model). The results indicate that the end‐member model provides a sufficient approximation for the elastic properties of Cr‐pyrope in calculating the density and velocity of the subcontinental lithospheric mantle (SCLM). We modeled the densities and velocities of three typical types of SCLM (Archon, Proton, and Tecton) in order to investigate how the variation of chemical composition influences the SCLM. We obtained that the compositional change from the Archon to the Tecton increases the density of the SCLM significantly, which can be an important prerequisite for SCLM delamination. However, the compositional variation only slightly changes the velocity of the SCLM and the change is within the uncertainty of the calculation. Moreover, in comparison to the velocity,ρ/V_Pandρ/V_Sare much more sensitive to the compositional change of the SCLM.

    

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