The Effect of Surface Brightness Dimming in the Selection of High-z
  Galaxies
  Cosmological surface brightness dimming of the form $(1+z)^{-4}$ affects all
sources. The strong dependence of surface brightness dimming on redshift z
suggests the presence of a selection bias when searching for high-redshift
galaxies, i.e. we tend to detect only those galaxies with a high surface
brightness (SB). However, unresolved knots of emission are not affected by SB
dimming, thus providing a way to test the clumpiness of high-z galaxies. Our
strategy relies on the comparison of the total flux detected for the same
source in surveys characterized by different depth. For all galaxies, deeper
images permit the better investigation of low-SB features. Cosmological SB
dimming makes these low-SB features hard to detect when going to higher and
higher redshifts. We used the GOODS and HUDF Hubble Space Telescope legacy
datasets to study the effect of SB dimming on low-SB features of high-redshift
galaxies and compare it to the prediction for smooth sources. We selected a
sample of Lyman-break galaxies at z~4 (i.e. B-band dropouts) detected in all of
the datasets and found no significant trend when comparing the total magnitudes
measured from images with different depth. Through Monte Carlo simulations we
derived the expected trend for galaxies with different SB profiles. The
comparison to the datahints at a compact distribution for most of the
rest-frame ultraviolet light emitted from high-z galaxies.
