Paper detail

The bright-end of the luminosity function at z~9

We report new constraints on the galaxy luminosity function at z~9 based on observations carried out with ESO/VLT FORS2, HAWK-I and X-Shooter around the lensing cluster A2667, as part of our project aimed at selecting z~7-10 candidates accessible to spectroscopy. Only one J-dropout source was selected in this field fulfilling the color and magnitude criteria. This source was recently confirmed as a mid-z interloper based on X-Shooter spectroscopy. The depth and the area covered by our survey are well suited to set strong constraints on the bright-end of the galaxy luminosity function and hence on the star formation history at very high redshift. The non-detection of reliable J-dropout sources over the ~36arcmin2 field of view towards A2667 was used to carefully determine the lens-corrected effective volume and the corresponding upper-limit on the density of sources. The strongest limit is obtained for Phi(M_{1500}=-21.4+/-0.50)<6.70x10^{-6}Mpc^{-3}mag^{-1} at z~9. A maximum-likelihood fit of the luminosity function using all available data points including the present new result yields M*>-19.7 with fixed alpha=-1.74 and Phi*=1.10x10^{-3}Mpc^{-3}. The corresponding star formation rate density should be rho_{SFR}<5.97x10^{-3}M_{solar}/yr/Mpc^{3} at z~9. These results are in good agreement with the most recent estimates already published in this range of redshift and for this luminosity domain. This new result confirms the decrease in the density of luminous galaxies at very high-redshift, hence providing strong constraints for the design of future surveys aiming to explore the very high-redshift Universe.