We present the first photometric redshift distribution for a large
sample of 870 μm submillimeter galaxies (SMGs) with robust
identifications based on observations with ALMA. In our analysis we
consider 96 SMGs in the Extended Chandra Deep Field South, 77 of which
have 4-19 band photometry. We model the SEDs for these 77 SMGs, deriving
a median photometric redshift of z phot = 2.3 ± 0.1.
The remaining 19 SMGs have insufficient photometry to derive photometric
redshifts, but a stacking analysis of Herschel observations confirms
they are not spurious. Assuming that these SMGs have an absolute H-band
magnitude distribution comparable to that of a complete sample of z ~
1-2 SMGs, we demonstrate that they lie at slightly higher redshifts,
raising the median redshift for SMGs to z phot = 2.5 ±
0.2. Critically we show that the proportion of galaxies undergoing an
SMG-like phase at z >= 3 is at most 35% ± 5% of the total
population. We derive a median stellar mass of M sstarf = (8
± 1) × 1010 M ⊙, although there
are systematic uncertainties of up to 5 × for individual sources.
Assuming that the star formation activity in SMGs has a timescale of
~100 Myr, we show that their descendants at z ~ 0 would have a space
density and MH distribution that are in good agreement with
those of local ellipticals. In addition, the inferred mass-weighted ages
of the local ellipticals broadly agree with the look-back times of the
SMG events. Taken together, these results are consistent with a simple
model that identifies SMGs as events that form most of the stars seen in
the majority of luminous elliptical galaxies at the present day.