Emission-line spectroscopy in NGC 891

Here, we test a dynamical equilibrium model of the eDIG layer in NGC 891, where we ask whether the thermal, turbulent, magnetic field, and cosmic-ray pressure gradients are sufficient to support the layer. In optical emission-line spectroscopy from the SparsePak integral field unit on the WIYN 3.5m telescope, the H{alpha} emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of R_min_<=R<=8kpc, where R_min_>=2kpc.

We find that the thermal ({sigma}_th_=11km/s) and turbulent ({sigma}_turb_=25km/s) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of h_z_=1.0kpc. Using a literature analysis of radio continuum observations from the CHANG-ES survey, we demonstrate that the magnetic field and cosmic-ray pressure gradients are sufficient to stably support the gas at R>=8kpc if the cosmic rays are sufficiently coupled to the system ({gamma}_cr_=1.45).