changing the atmospheric seeing, and the lower plot shows the effect of varying the concentration. All other parameters are kept fixed at the preferred values.](./images/PLOT_conc "fig:"){width="0.85\columnwidth"}

Variation of model parameters {#sec:lbg_effect}
-----------------------------

In this section we explore to what extent variation of the parameters of the model affects the conclusion that LBGs are significantly less massive than predicted by the massive–halo model.

1.  We find that our results are not very sensitive to the exactly value of the seeing adopted. We repeated the entire analysis for values of 0.4arcsec and 0.6arcsec. The corresponding likelihood curves are shown in the top plot of Figure \[fig:lbg\_bayesians\], and compared to the curve for the fiducial value of 0.5arcsec. Over the range 0.4 – 0.6arcsec the probability for the massive–halo model varies over the range $0.006<p<0.032$.

2.  The lower plot shows the effect of varying the value of the concentration parameter $c$. Since the relation between $V_{c \rm
      7}$ and $V_h$ depends on $c$, varying $c$ changes not only the predicted rotation velocities but also the value of $\alpha(req)$, as indicated on the plot. For the range of $V_h$ specified by MMW a suitable range for the concentration parameter is $3<c<5$ (Bullock et al. 