Internal Kinematics of Blue Canada-France Redshift Survey Galaxies at Z ~ 0.6

Abstract

We present the results of a study of the internal kinematics of luminous star-forming galaxies in the 0<z<0.8 range, with the aim of investigating the nature of the blue galaxies that cause the largest changes in the luminosity function at z>=0.5. New kinematic data are analyzed for a sample of 24 galaxies from the Canada-France Redshift Survey (CFRS), 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 well-studied magnitude-limited survey (the CFRS). Our sample is therefore representative of the most rapidly changing one-third of the galaxy population in the 0<z<0.8 range. The 15 galaxies at z>0.45 have sizes (from Hubble Space Telescope images) and velocity widths σ_v (from emission lines) similar to those of typical local irregular galaxies. This is consistent with their morphologies and rest-frame colors; however, these galaxies are as bright as the brightest local irregular galaxies and roughly 2 mag brighter than the typical irregular galaxies 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.

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 NAS5-26555.