Evolution of the Fundamental Plane of 0.2<z<1.2 Early-type galaxies in the EGS
The Fundamental Plane relates the structural properties of early-type
galaxies such as its surface brightness and effective radius with its
dynamics. The study of its evolution has therefore important
implications for models of galaxy formation and evolution. This work
aims to identify signs of evolution of early-type galaxies through the
study of parameter correlations using a sample of 135 field galaxies
extracted from the Extended Groth Strip in the redshift range
0.2<z<1.2. Using DEEP2 data, we calculate the internal velocity
dispersions by extracting the stellar kinematics from absorption line
spectra, using a maximum penalized likelihood approach. Morphology was
determined through visual classification using the V+I images of ACS.
The structural parameters of these galaxies were obtained by fitting de
Vaucouleurs stellar profiles to the ACS I-band images, using the GALFIT
code. S\’ersic and bulge-to-disc decomposition models were also fitted
to our sample of galaxies, and we found a good agreement in the
Fundamental Plane derived from the three models. Assuming that effective
radii and velocity dispersions do not evolve with redshift, we have
found a brightening of 0.68 mag in the B-band and 0.52 mag in the g-band
at <z>=0.7. However, the scatter in the FP is reduced by half when
we allow the FP slope to evolve, suggesting a different evolution of
early-type galaxies according to their intrinsic properties. The study
of the Kormendy relation shows the existence of a population of very
compact (Re<2 Kpc) and bright galaxies (-21.5>Mg>-22.5), of
which there are only a small fraction (0.4%) at z=0. The evolution of
these compact objects is mainly caused by an increase in size that could
be explained by the action of dry minor mergers, and this population is
responsible for the evolution detected in the Fundamental Plane.