Internal Kinematics of Blue CFRS Galaxies at z ∼ 0.6 1

We present the results of a study of the internal kinematics of luminous starforming galaxies in the 0 < z < 0.8 range, with the aim of investigating the nature of the blue galaxies which cause the largest changes in the luminosity function at z ≥ 0.5. New kinematic data are analysed for a sample of 24 galaxies from the Canada-France Redshift Survey, most of them with rest-frame (U −V )AB ≤ 1.14. Unlike most previous studies, target galaxies were selected regardless of size and morphology, from a wellstudied magnitude-limited survey (the CFRS). Our sample is therefore representative of the most rapidly changing 1/3 of the galaxy population in the 0 < z < 0.8 range. The 15 galaxies at z > 0.45 have sizes (from HST images) and velocity widths σv (from emission lines) similar to those of typical local Irregulars. This is consistent with their morphologies and rest-frame colors; however, these galaxies are as bright as the brightest local Irregulars, and roughly 2 magnitudes brighter than typical Irregulars known nearby. We conclude that the increase in the number density of luminous blue galaxies at z ≥ 0.5 is mainly due to a population of small and unusually-bright late-type galaxies. Subject headings: galaxies: evolution — galaxies: fundamental parameters — galaxies: kinematics and dynamics Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Visiting Astronomer, Canada-France-Hawaii Telescope, which is operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.