The Ionized Gas in Nearby Galaxies as Traced by the [NII] 122 and 205 \mu m Transitions

Understand

The [NII] 122 and 205 \mu m transitions are powerful tracers of the ionized gas in the interstellar medium.

• By combining data from 21 galaxies selected from the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141 spatially resolved regions with a typical size of ~1 kiloparsec, with observations of both [NII] far-infrared lines.
• We measure [NII] 122/205 line ratios in the ~0.6-6 range, which corresponds to electron gas densities $n_e$~1-300 cm$^{-3}$, with a median value of $n_e$=30 cm$^{-3}$.
• Variations in the electron density within individual galaxies can be as a high as a factor of ~50, frequently with strong radial gradients.