%0 Journal Article
%T Luminous early-type field galaxies at z ~ 0.4 - II. Star-formation history and space density
%A J. P. Willis
%A P. C. Hewett
%A S. J. Warren
%A G. F. Lewis
%J Physics
%D 2002
%I arXiv
%R 10.1046/j.1365-8711.2002.05970.x
%X We present a combined photometric and spectroscopic analysis of the star formation history and space density of a sample of 485 luminous, M_V - 5 log h < -20.5, field early-type galaxies at redshifts 0.3 < z < 0.6. The observed b_Jori colours as a function of redshift, mean absorption line strengths and [OII] 3727 emission properties are used to constrain the star formation history of the galaxies. The mean star formation history of the early-type galaxy sample is consistent with an old (z_f>1), passively evolving luminosity-weighted stellar population. Twenty-one percent of the sample possess detectable [OII] 3727 emission consistent with a low level (<1 M_solar/yr) of on-going star formation. Parametric and non-parametric estimates of the space density of the sample are derived. The integrated luminosity density at z ~ 0.4, allowing only for passive luminosity evolution, is in excellent agreement with the local, (<z> = 0.1), luminosity density of early-type galaxies. Overall, the sample properties are consistent with a galaxy formation scenario in which the majority of luminous field early-type galaxies formed at redshifts z>1 and have largely evolved passively since the formation epoch.
%U http://arxiv.org/abs/astro-ph/0208224v2