Galaxy and Mass Assembly (GAMA): A $\textit{WISE}$ study of the activity
  of emission-line systems in G23
  We present a detailed study of emission-line systems in the GAMA G23 region,
making use of $\textit{WISE}$ photometry that includes carefully measured
resolved sources. After applying several cuts to the initial catalogue of
$\sim$41,000 galaxies, we extract a sample of 9,809 galaxies. We then compare
the spectral diagnostic (BPT) classification of 1154 emission-line galaxies
(38$\%$ resolved in W1) to their location in the $\textit{WISE}$ colour-colour
diagram, leading to the creation of a new zone for mid-infrared "warm" galaxies
located 2$\sigma$ above the star-forming sequence, below the standard
$\textit{WISE}$ AGN region. We find that the BPT and $\textit{WISE}$ diagrams
agree on the classification for 85$\%$ and 8$\%$ of the galaxies as non-AGN
(star forming = SF) and AGN, respectively, and disagree on $\sim$7$\%$ of the
entire classified sample. 39$\%$ of the AGN (all types) are broad-line systems
for which the [\ion{N}{ii}] and [H$\alpha$] fluxes can barely be disentangled,
giving in most cases spurious [\ion{N}{ii}]/[H$\alpha$] flux ratios. However,
several optical AGN appear to be completely consistent with SF in
$\textit{WISE}$. We argue that these could be low power AGN, or systems whose
hosts dominate the IR emission. Alternatively, given the sometimes high
[\ion{O}{iii}] luminosity in these galaxies, the emission lines may be
generated by shocks coming from super-winds associated with SF rather than the
AGN activity. Based on our findings, we have created a new diagnostic: [W1-W2]
vs [\ion{N}{ii}]/[H$\alpha$], which has the virtue of separating SF from AGN
and high-excitation sources. It classifies 3$\sim$5 times more galaxies than
the classic BPT
