Internal Kinematics of Blue Canada-France Redshift Survey Galaxies at [CLC][ITAL]z[/ITAL][/CLC] ∼ 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 σv (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.