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The observed scale heights of extraplanar diffuse ionized gas (eDIG) layersexceed their thermal scale heights by a factor of a few in the Milky Way andother nearby edge-on disk galaxies. Here, we test a dynamical equilibrium modelof the extraplanar diffuse ionized gas layer in NGC 891, where we ask whetherthe thermal, turbulent, magnetic field, and cosmic ray pressure gradients aresufficient to support the layer. In optical emission line spectroscopy from theSparsePak integral field unit on the WIYN 3.5-meter telescope, the H-alphaemission in position-velocity space suggests that the eDIG is found in a ringbetween galactocentric radii of R_min <= R <= 8 kpc, where R_min >= 2 kpc. Wefind that the thermal (sigma_th = 11 km/s) and turbulent (sigma_turb = 25 km/s)velocity dispersions are insufficient to satisfy the hydrostatic equilibriumequation given an exponential electron scale height of h_z = 1.0 kpc. Using aliterature analysis of radio continuum observations from the CHANG-ES survey,we demonstrate that the magnetic field and cosmic ray pressure gradients aresufficient to stably support the gas at R >= 8 kpc if the cosmic rays aresufficiently coupled to the system (gamma_cr = 1.45). Thus, a stable dynamicalequilibrium model is viable only if the extraplanar diffuse ionized gas isfound in a thin ring around R = 8 kpc, and non-equilibrium models such as agalactic fountain flow are of interest for further study.

Testing a Dynamical Equilibrium Model of the Extraplanar Diffuse Ionized Gas in NGC 891