Internal kinematics of CFRS galaxies at z approximately equal to 0.6

The internal kinematics of a galaxy are closely related to its dynamical mass, and can help place constraints an the type of galaxy that is being observed; in particular, different types of galaxies show characteristic scaling relations of size and velocity width sigmav, or rotation velocity Vrot. In principle, these scaling relations provide clues about the nature of a galaxy independently of any changes in luminosity or morphology that may be caused by bursts of star formation.; This thesis is based on 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 30 galaxies from the Canada-France Redshift Survey, most of them with rest-frame (U - V)AB ≤ 1/2. 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 1/3 of the galaxy population in the 0 < z < 0.8 range. The 17 galaxies at z > 0.45 have sizes (from HST images) and velocity widths sigma v (from emission lines) similar to those of typical local Irregular galaxies or very small late-type Spiral galaxies. This is consistent with their morphologies (Brinchmann et al. 1998) and rest-frame colors; however, these galaxies are as bright as the brightest local Irregular galaxies, and roughly 2 magnitudes brighter than 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. This could be caused by either an increase in luminosity of some fraction of the population of small galaxies, by an increase in the number density of said population, or by a combination of both density and luminosity evolution.