2016ApJ...832..118B -
Astrophys. J., 832, 118-118 (2016/December-1)
Testing a dynamical equilibrium model of the extraplanar diffuse ionized gas in NGC 891.
BOETTCHER E., ZWEIBEL E.G., GALLAGHER III J.S. and BENJAMIN R.A.
Abstract (from CDS):
The observed scale heights of extraplanar diffuse ionized gas (eDIG) layers exceed their thermal scale heights by a factor of a few in the Milky Way and other nearby edge-on disk galaxies. 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 3.5 m telescope, the Hα emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of R{min}\leqslant R\leqslant 8 kpc, where R{min}\geqslant 2 kpc. We find that the thermal (σth=11 km s–1) and turbulent (σturb=25 km s–1) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of hz=1.0 kpc. 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\geqslant 8 kpc if the cosmic rays are sufficiently coupled to the system (γcr=1.45). Thus, a stable dynamical equilibrium model is viable only if the eDIG is found in a thin ring around R = 8 kpc, and nonequilibrium models such as a galactic fountain flow are of interest for further study.
Abstract Copyright:
© 2016. The American Astronomical Society. All rights reserved.
Journal keyword(s):
cosmic rays - galaxies: individual: NGC 891 - galaxies: ISM - ISM: kinematics and dynamics - ISM: magnetic fields - ISM: magnetic fields
VizieR on-line data:
<Available at CDS (J/ApJ/832/118): table3.dat>
Simbad objects:
5
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