Galaxy surveys 325Figure 11.3. A compilation of number counts in the U, B, I, K bands from different
surveys (Fergusonet al2000 and references therein). Full symbols are from the
HDF North and South, open symbols from several ground-based surveys. Full lines
are no-evolution models obtained integrating the observed local luminosity function for
(m,)=( 0. 3 , 0. 7 ).
significant impact on the selection function and completeness of the sample by
absorbing the UV part of the continuum and selectively suppressing different
emission lines.
11.3.3 Galaxy counts and evolution
We show in figure 11.3 a compilation of number counts from ground-based and
HST surveys over a 13 magnitude range, as observed in the U, B, I and K
passbands (see Fergusonet al2000). Each set is displaced by a factor of 10 for
clarity. Full curves represent the theoretical expectations obtained by integrating
the local luminosity function assumingno evolutionand(m,)=( 0. 3 , 0. 7 ),
as described in section 11.3.3. These no-evolution (NE) models make reasonable
assumptions on the morphological mix of the local galaxy population (relative
fraction of irregulars, spirals, ellipticals), their LFs and their SEDs (required to