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ABSTRACT We characterize the kinematic and magnetic properties of H i filaments located in a high Galactic latitude region (165° < α < 195° and 12° < δ < 24°). We extract three-dimensional filamentary structures using fil3d from the Galactic Arecibo L-Band Feed Array H i (GALFA-H i) survey 21-cm emission data. Our algorithm identifies coherent emission structures in neighbouring velocity channels. Based on the mean velocity, we identify a population of local and intermediate velocity cloud (IVC) filaments. We find the orientations of the local (but not the IVC) H i filaments are aligned with the magnetic field orientations inferred from Planck 353 GHz polarized dust emission. We analyse position–velocity diagrams of the velocity-coherent filaments, and find that only 15 per cent of filaments demonstrate significant major-axis velocity gradients with a median magnitude of 0.5 km s−1 pc−1, assuming a fiducial filament distance of 100 pc. We conclude that the typical diffuse H i filament does not exhibit a simple velocity gradient. The reported filament properties constrain future theoretical models of filament formation. 

Abstract Dwarf galaxies are found to have lost most of their metals via feedback processes; however, there still lacks consistent assessment on the retention rate of metals in their circumgalactic medium (CGM). Here we investigate the metal content in the CGM of 45 isolated dwarf galaxies withM_*= 10^6.5–9.5M_⊙(M_200m= 10^10.0–11.5M_⊙) using the Hubble Space Telescope/Cosmic Origins Spectrograph. While Hi(Lyα) is ubiquitously detected (89%) within the CGM, we find low detection rates (≈5%–22%) in Cii, Civ, Siii, Siiii, and Siiv, largely consistent with literature values. Assuming these ions form in the cool (T≈ 10⁴K) CGM with photoionization equilibrium, the observed Hiand metal column density profiles can be best explained by an empirical model with low gas density and high volume filling factor. For a typical galaxy withM_200m= 10^10.9M_⊙(median of the sample), our model predicts a cool gas mass ofM_CGM,cool∼ 10^8.4M_⊙, corresponding to ∼2% of the galaxy’s baryonic budget. Assuming a metallicity of 0.3 Z_⊙, we estimate that the dwarf galaxy’s cool CGM likely harbors ∼10% of the metals ever produced, with the rest either in more ionized states in the CGM or transported to the intergalactic medium. We further examine the EAGLE simulation and show that Hiand low ions may arise from a dense cool medium, while Civarises from a diffuse warmer medium. Our work provides the community with a uniform data set on dwarf galaxies’ CGM that combines our recent observations, additional archival data and literature compilation, which can be used to test various theoretical models of dwarf galaxies.