The UDF05 follow-up of the hubble ultra deep field. II. Constraints on reionization from z-dropout galaxies

Abstract

We detect three (plus one less certain) z 850-dropout sources in two separate fields (Hubble Ultra Deep Field and NICP34) of our UDF05 Hubble Space Telescope Near-Infrared Camera and Multi-Object Spectrometer images. These z 7 Lyman-break Galaxy (LBG) candidates allow us to constrain the Luminosity Function (LF) of the star-forming galaxy population at those epochs. By assuming a change in only M * and adopting a linear evolution in redshift, anchored to the measured values at z 6, the best-fit evolution coefficient is found to be 0.43 0.19 mag per unit redshift (0.36 0.18, if including all four candidates), which provides a value of M *(z = 7.2) = -19.7 0.3. This implies a drop in the lumin..