Evolution of the fundamental plane of 0.2  <  z  <  1.2 early-type galaxies in the EGS^⋆

¹ Instituto de Astrofísica de Canarias (IAC), C/vía Láctea S/N, 38200 La Laguna, Spain
e-mail: mfernan@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, Spain
³ Herschel Science Centre, INSA/ESAC, Madrid, Spain

Received: 9 July 2010
Accepted: 18 October 2010

Abstract

Context. The fundamental plane links the structural properties of early-type galaxies such as its surface brightness and effective radius with its dynamics. The study of the fundamental plane evolution therefore has important implications for models of galaxy formation and evolution.

Aims. This work aims to identify signs of evolution of early-type galaxies through the study of parameter correlations such as the fundamental plane, the Kormendy, and the Faber-Jackson relations, using a sample of 135 field galaxies extracted from the Extended Groth Strip in the redshift range 0.2 < z < 1.2.

Methods. We calculate the internal velocity dispersions with DEEP2 data by extracting the stellar kinematics from absorption line spectra, using a maximum penalized-likelihood approach. Morphology was determined through visual classification of 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 with the GALFIT code. To check the effect on the fundamental plane of the structural parameters, Sérsic and bulge-to-disc decomposition models were fitted to our sample of galaxies. A good agreement was found in the fundamental plane derived from the three models.

Results. Assuming that effective radii and velocity dispersions do not evolve with redshift, we 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 fundamental plane for our high-redshift sample is reduced by half when we allow the fundamental plane slope to evolve, suggesting a different evolution of early-type galaxies according to their intrinsic properties such as total mass, size, or luminosity. The study of the Kormendy relation shows a population of very compact (R_e < 2 Kpc) and bright galaxies (−21.5 > M_g > −22.5), of which there are only a small fraction (0.4%) at z = 0. Studying the luminosity-size and stellar mass-size relations, we show that 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. We also detect an evolution in the fundamental plane caused mainly by this population of very compact and bright galaxies. Unfortunately, we cannot distinguish a change in the slope from an increase in the scatter of the fundamental plane because our high-redshift sample is biased to the brightest objects.