[@Prieto2016]. We note the caveat that if the lines in our spectra are excited by AGN activity, the calibrations used to estimate the metallicity may not always be valid.

To test the AGN scenario, we look at the mid-infrared colours. @Stern2012 identify a colour cut $W1-W2>0.8$Vega mag to select AGN from WISE data. For the host of AT2019qiz, we find $W1-W2\approx0$Vega mag. At most a few percent of AGN have such a blue $W1-W2$ colour [@Assef2013]. @Wright2010 employ a two-dimensional cut using the $W1-W2$ and $W2-W3$. The host of AT2019qiz has $W2-W3=1.8$mag, consistent with other spiral galaxies. Thus the emission detected by WISE is dominated by the galaxy, not an AGN.

The ratio of X-ray to \[O III\] luminosity can also be used as an AGN diagnostic. Converting the X-rays to the 2-20keV band using our best-fit power-law, we measure a mean $L_X/L_{\rm [O~III]}=2.4\pm0.2$, which is consistent with a typical AGN [@Heckman2005]. However, the X-ray luminosity is only 0.03% of the Eddington luminosity for a SMBH of $10^6$. Moreover, the temporal variation in the luminosity and hardness of the X-rays during the flare suggests a significant fraction of this emission comes from the TDE itself, rather than an existing AGN. 