On the stability of morphological parameters measurements with redshift

Ferreira, L.; Ferrari, F.; Mendes de Oliveira, C;

Measuring the structural properties of galaxies at different redshifts is a 
crutial step towards understanding how galaxies form and evolve. Traditional 
morphological and structural parameters (e.g. Sérsic intensity, effective 
radius and index, concentration, asymmetry,Petrosian Radius, Gini coefficient) 
may be dependent on the image sampling, point spread function and signal to 
noise ratio.  In order to measure how the morphology of galaxies evolve, we 
need to know how robust our measurements are at different redshifts. In this 
context, we used the FERENGI application to simulate the effect of observing 
the same galaxy at different redshifts. We applied the procedure to the FREI 
and EFIGI databases to artificially redshift local galaxies out to a distance 
of 2 Gpc (z~0.5) and we then used the FOTOMETRIKA package to measure several 
morphological and structural parameters. In this way, we were able to check how 
the measurements behave as the spatial resolution and the signal to noise 
decreases. Those parameters that depend on the distance can be corrected for 
and compared with other measurements. Other parameters, such as asymmetry (both 
traditionally measured and an improved version) are found to present stable 
values with redshift.