Top: distribution of redshifts of the studied SMGs. The blue filled histogram shows the redshift distribution of the SMGs AzTEC1−15, while the red filled histogram shows that of AzTEC16−30. The open grey histogram indicates the redshift distribution of the combined sample (AzTEC1−30). The vertical dashed lines mark the corresponding median redshifts (blue: ; red: ; grey: ). The lower redshift limits (see Table 4) were placed in the bins corresponding to those values, but the indicated median redshifts were properly derived through survival analysis. Bottom: probability density distribution of the redshifts of AzTEC1−30. The light grey curve shows the unsmoothed distribution, and the black curve represents the Gaussian-smoothed kernel density estimate (see text for details). The median redshift and the 68% CI are indicated.