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Abstract The circumgalactic medium (CGM) contains information on gas flows around galaxies, such as accretion and supernova-driven winds, which are difficult to constrain from observations alone. Here, we use the high-resolution TNG50 cosmological magnetohydrodynamical simulation to study the properties and kinematics of the CGM around star-forming galaxies in 10 11.5 –10 12 M ⊙ halos at z ≃ 1 using mock Mg ii absorption lines, which we generate by postprocessing halos to account for photoionization in the presence of a UV background. We find that the Mg ii gas is a very good tracer of the cold CGM, which is accreting inward at inflow velocities of up to 50 km s −1 . For sight lines aligned with the galaxy’s major axis, we find that Mg ii absorption lines are kinematically shifted due to the cold CGM’s significant corotation at speeds up to 50% of the virial velocity for impact parameters up to 60 kpc. We compare mock Mg ii spectra to observations from the MusE GAs FLow and Wind (MEGAFLOW) survey of strong Mg ii absorbers (EW 2796 Å 0 > 0.5 Å). After matching the equivalent-width (EW) selection, we find that the mock Mg ii spectra reflect the diversity of observed kinematics and EWs from MEGAFLOW, even though the sight lines probe a very small fraction of the CGM. Mg ii absorption in higher-mass halos is stronger and broader than in lower-mass halos but has qualitatively similar kinematics. The median-specific angular momentum of the Mg ii CGM gas in TNG50 is very similar to that of the entire CGM and only differs from non-CGM components of the halo by normalization factors of ≲1 dex. 

Abstract We  present the demography of the dynamics and gas mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of 0.015–0.195Z_⊙and low stellar masses of 10⁴–10⁸M_⊙in the local universe. We conduct deep optical integral field spectroscopy (IFS) for the low-mass EMPGs with the medium-high resolution (R= 7500) grism of the 8 m Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate the Hαemission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the Hαlines by the fitting of three-dimensional disk models. We obtain an average maximum rotation velocity (v_rot) of 15 ± 3 km s⁻¹and an average intrinsic velocity dispersion (σ₀) of 27 ± 10 km s⁻¹for 15 spatially resolved EMPGs out of 33 EMPGs, and find that all 15 EMPGs havev_rot/σ₀< 1 suggesting dispersion-dominated systems. There is a clear decreasing trend ofv_rot/σ₀with the decreasing stellar mass and metallicity. We derive the gas mass fraction (f_gas) for all 33 EMPGs, and find no clear dependence on stellar mass and metallicity. Thesev_rot/σ₀andf_gastrends should be compared with young high-zgalaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe. 

Abstract We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098Z_⊙) and low stellar masses (10^4.7–10^7.6M_⊙). Taking deep medium/high-resolution (R∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hαemission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed Hαflux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (v_rot) of 5–23 km s⁻¹smaller than the velocity dispersions (σ₀) of 17–31 km s⁻¹, indicating dispersion-dominated (v_rot/σ₀= 0.29–0.80 < 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions off_gas≃ 0.9–1.0. Comparing our results with other Hαkinematics studies, we find thatv_rot/σ₀decreases andf_gasincreases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high-z(z∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations atz∼ 7.