Sub-L* Galaxies at Redshifts z 4, 3, and 2: Their UV Luminosity Function and Luminosity Density

Original · EN

We use very deep (Rₗim=27) UGRI imaging to study the evolution of the faint end of the UV-selected galaxy luminosity function from z 4 to z 2. We find that the luminosity function evolves with time and that this evolution is differential with luminosity: the number of sub-L* galaxies increases from z 4 to z 3 by at least a factor of 2.3, while the bright end of the LF remains unchanged. Potential systematic biases restrict our ability to draw strong conclusions at lower redshifts, z 2, but we can say that the number density of sub-L* galaxies at z 2.2 is at least as high as it is at z 3. Turning to the UV luminosity density of the Universe, we find that the luminosity density starts dropping with increasing redshift already beginning at z=3 (earlier than recently thought - Steidel et al. 1999) and that this drop is dominated by the same sub-L* galaxies that dominate the evolution of the LF. This differential evolution of the luminosity function suggests that differentially comparing key diagnostics of dust, stellar populations, etc. as a function of z and L should let us isolate the key mechanisms that drive galaxy evolution at high redshift.