reliable. Applying the calibration of @Marino2013, valid over a wider range, we find a slightly lower metallicity of $12+\log({\rm O/H})=8.63$, consistent with solar metallicity.

                    Line                    Flux ($10^{-16}$ergs$^{-1}$cm$^{-2}$)
  ---------------------------------------- ---------------------------------------
                  H$\beta$                              $7.9 \pm 1.7$
        [\[O III\] $\lambda5007$]{}                     $8.0 \pm 3.1$
         [\[O I\] $\lambda6300$]{}                         $<3.0$
                 H$\alpha$                             $14.2 \pm 3.8$
         [\[N II\] $\lambda6584$]{}                     $7.6 \pm 1.9$
   [\[S II\] $\lambda\lambda6717,6731$]{}               $6.3 \pm 1.0$
                                                        $\log$ ratio
          [\[O III\]]{} / H$\beta$                     $0.04 \pm 0.25$
          [\[N II\]]{} / H$\alpha$                    $-0.25 \pm 0.14$
          [\[S II\]]{} / H$\alpha$                    $-0.32 \pm 0.16$
          [\[O I\]]{} / H$\alpha$                      $\lesssim -0.7$

  : Host emission line fluxes and BPT line ratios [@Baldwin1981], averaged over the X-shooter spectra.[]{data-label="tab:bpt"}

Ratios of these lines are used in the Baldwin-Phillips-Terlovich (BPT) diagram [@Baldwin1981] to probe the ionization mechanism of the gas. The ratios we measure for the host of AT2019qiz (Table \[tab:bpt\]) lie intermediate between the main sequence of star-forming galaxies and galaxies with ionization dominated by an active galactic nucleus (AGN). This could be evidence of a weak AGN, or another source of ionization such as supernova shocks or evolved stars [@Kewley2001]. Several other TDE hosts lie in a similar region of the BPT parameter space [@Wevers2019; @French2020rev], while a number show direct evidence of AGN ionisation 