of the stellar mass in galaxies is the specific star formation rate (SSFR) i.e. the star formation rate per unit mass. It is well known that more massive galaxies have lower SSFR (e.g. Erb et al. 2006) and that at a fixed stellar mass, the SSFR declines with increasing redshift (e.g. Reddy et al. 2006 , Feulner et al. 2005). In Figure \[fig:ssfr1\] we plot the SSFR vs total stellar mass: the two quantities are anti-correlated with high probability (a Spearman Rank test gives a correlation coefficient of -0.6). In practice, galaxies with lower stellar mass are assembling a much higher fraction of their mass with the current star formation episode, compared to more massive objects.

  Property                          $LBG_L$                      $LBG_N$                     P(K-S)
  --------------------------------- ---------------------------- --------------------------- --------
  $N_{gal}$                         66                           66                          
  L(1400) (cgs)                     $5.9\pm0.6 \times 10^{28}$   $6.0\pm0.6 \times10^{28}$   0.993
  $SFR_{SED}$ ($M_\odot yr^{-1}$)   13.2 $\pm 4.2$               16.0$\pm 11$                0.367
  $SFR_{UV}$ ($M_\odot yr^{-1}$)    15.6$\pm 1.9$                12.9$\pm 3.4$               0.414
  Age (Myrs)                        250$\pm$35                   316$\pm$40                  0.136
  E(B-V)                            0.03$\pm0.009$               0.06$\pm0.012$              0.012
  Mass ($M_\odot$)                  3.4$\pm 1.5 \times 10^9$     8.7$\pm 1.2 \times 10^9$    0.000

  : Average properties of and derived from the SED fitting with the Charlot & Bruzual (2009) models

\[popgal\]

![The SSFR vs stellar mass. The two dashed lines indicate 