This paper illustrates how mock observational samples of high–redshift galaxies with sophisticated selection criteria can be extracted from the predictions of galics , a hybrid model of hierarchical galaxy formation that couples the outputs of large cosmological simulations , and semi–analytic recipes to describe dark matter collapse , and the physics of baryons respectively .
As an example of this method , we focus on the properties of Lyman Break Galaxies at redshift z \sim 3 ( hereafter LBGs ) in a \Lambda CDM cosmology .
With the momaf software package described in a companion paper , we generate a mock observational sample with selection criteria as similar as possible to those implied in the actual observations of z \sim 3 LBGs by ( ) .
We need to introduce an additional “ maturity ” criterion to circonvene subtle effects due to mass resolution in the simulation .
We predict a number density of 1.15 arcmin ^ { -2 } at R \leq 25.5 , in good agreement with the observed number density 1.2 \pm 0.18 arcmin ^ { -2 } .
Our model allows us to study the efficiency of the selection criterion to capture z \sim 3 galaxies .
We find that the colour contours designed from models of spectrophotometric evolution of stellar populations are able to select more “ realistic ” galaxies issued from models of hierarchical galaxy formation .
We quantify the fraction of interlopers ( 12 % ) , and the selection efficiency ( 85 % ) , and we give estimates of the cosmic variance .
We then study the clustering properties of our model LBGs .
They are hosted by halos with masses \sim 1.6 \times 10 ^ { 12 } M _ { \odot } , with a linear bias parameter that decreases with increassing scale from b = 5 to 3 .
The amplitude and slope of the 2D correlation function is in good agreement with the data .
We investigate a series of physical properties : UV extinction ( a typical factor 6.2 at 1600 Å ) , stellar masses , metallicities , and Star Formation Rates , and we find them to be in general agreement with observed values .
The model also allows us to make predictions at other optical and IR/submm wavelengths , that are easily accessible though queries to a web interfaced relational database .
Looking into the future of these LBGs , we predict that 75 % of them end up as massive ellipticals and lenticulars today , even though only 35 % of all our local ellipticals and lenticulars are predicted to have a LBG progenitor .
In spite of some shortcomings that come from our simplifying assumptions and the subtle propagation of mass resolution effects , this new ’ mock observation ’ method clearly represents a first step toward a more accurate comparison between hierarchical models of galaxy formation and real observational surveys .