We present UV luminosity functions ( LFs ) at 1500 Å derived from the HST Early Release Science WFC3/UVIS data acquired over \sim 50 arcmin ^ { 2 } of the GOODS-South field .
The LFs are determined over the entire redshift range z = 0.75 - 2.5 using two methods , similar to those used at higher redshifts for Lyman Break Galaxies ( LBGs ) : ( 1 ) 13-band UV+optical+NIR photometric redshifts to study galaxies in the range z = 0.5 - 2 in three bins of dz = 0.5 , and ( 2 ) dropout samples in three redshift windows centered at z \sim 1.5 , z \sim 1.9 , and z \sim 2.5 .
The characteristic luminosity dims by 1.5 mag from z = 2.5 to z = 0.75 , consistent with earlier work .
However , the other Schechter function parameters , the faint-end slope and the number density , are found to be remarkably constant over the range z = 0.75 - 2.5 .
Using these LF determinations we find the UV luminosity density to increase by \sim 1.4 dex according to ( 1 + z ) ^ { 2.58 \pm 0.15 } from z \sim 0 to its peak at z \sim 2.5 .
Strikingly , the inferred faint-end slopes for our LFs are all steeper than \alpha = -1.5 , in agreement with higher-redshift LBG studies .
Since the faint-end slope in the local universe is found to be much flatter with \alpha \simeq - 1.2 , this poses the question as to when and how the expected flattening occurs .
Despite relatively large uncertainties , our data suggest \alpha \simeq - 1.7 at least down to z \sim 1 .
These new results from such a shallow early dataset demonstrate very clearly the remarkable potential of WFC3/UVIS for the thorough characterization of galaxy evolution over the full redshift range z \sim 0.5 to z \sim 3 .