The difference between the observed ZTF uncertainties and the model uncertainties.
Prior to ZTF DR1 there were reports of inaccurate photometric uncertainties.
The error models were replaced with empirical values. However, the current
model uncertainties are based on a fit to the scatter observed within individual
full quadrants (in the above figure field 810, ccd 4, quadrant 1,
ZTF r < 17.5). The varying colours in the plot show difference between
the observed source rms and the model uncertainties for individual sources.
Red sources have larger than predicted scatter, green near predicted,
and blue, smaller.
Conclusions:
The actual photometric scatter varies spatially
within a quadrant. This is expected due to edge effects, vignetting, etc.
Thus, although current ZTF photometric error estimates are now good, they
are not completely accurate.
Note: this analysis was not done using the full error model as it was being updated at the time. However, the spatial trend will certainly still exist.
Todo:
Create a new uncertainly model that includes spatial variation.
Investigate differences between quadrants.