A Consistent Comparison of Bias Models using Observational Data
  We investigate five different models for the dark matter halo bias, ie., the
ratio of the fluctuations of mass tracers to those of the underlying mass, by
comparing their cosmological evolution using optical QSO and galaxy bias data
at different redshifts, consistently scaled to the WMAP7 cosmology. Under the
assumption that each halo hosts one extragalactic mass tracer, we use a
$\chi^2$ minimization procedure to determine the free parameters of the bias
models as well as to statistically quantify their ability to represent the
observational data. Using the Akaike information criterion we find that the
model that represents best the observational data is the Basilakos & Plionis
(2001; 2003) model with the tracer merger extension of Basilakos, Plionis &
Ragone-Figueroa (2008) model. The only other statistically equivalent model, as
indicated by the same criterion, is the Tinker et al. (2010) model. Finally, we
find an average, over the different models, dark matter halo mass that hosts
optical QSOs of: $M_h\simeq 2.7 (\pm 0.6) \times 10^{12} h^{-1} M_{\odot}$,
while the corresponding value for optical galaxies is: $M_h\simeq 6.3 (\pm 2.1)
\times 10^{11} h^{-1} M_{\odot}$.
