 the actual flux and noise distribution in real images. These simulations are described in detail by @sanc04a. We applied the peak subtraction nucleus removal as well as [[galfit]{}]{} to a set of $\sim$2000 quasar images created in this way. Comparing input and output parameter values yielded mean magnitude offsets as well as statistical errors for the individual host galaxy magnitudes (Fig. \[fig:corrs\_and\_errors\_z\]).

The simulations give reliability regions and error bars. The left panel in Figure \[fig:corrs\_and\_errors\_z\] shows which magnitudes are recovered for a given synthetic host galaxy. Since the input set covers a large range of different morphological configurations, scale lengths, nucleus-to-host ratios, etc., the recovered values will scatter. Close to the detection limit, the scatter and the corrections grow rapidly as a function of magnitude; additionally, the ability to differentiate between different morphological types will generally be lost. The combination of these effects is reflected in the spread of the output of the simulations. This measured spread is a direct estimate for the uncertainties of the total flux (right panel in Figure \[fig:corrs\_and\_errors\_z\]).

From these simulations we adopt approximate regions in brightness where host galaxy magnitudes can be reliably determined, with correction of 0.25 to a maximum of 0.6 mag. These regions go down to $\mathrm{{F606W}}=26.2$, $\mathrm{{F850LP}}=24.6$ for the peak subtraction method and the present data. Outside the corrections and errors increase. In three cases, marked in Table \[tab:results\_vz\] with ‘?’ in column $Z_\mathrm{hg}$, the observed magnitudes extend to outside these regions; here we continue using the derived corrections for these three objects, but the so derived host galaxies are more uncertain and their magnitudes should be taken with care. Notice that the [F850LP]{} band data are substantially shallower than the [F606W]{} band, mainly a consequence of the ACS detector sensitivity.

![image](f4