We study the sub-mm properties of color–selected galaxies via a stacking analysis applied for the first time to interferometric data at sub-mm wavelengths .
We base our study on 344 GHz ALMA continuum observations of \sim 20 ^ { \prime \prime } –wide fields centered on 86 sub-mm sources detected in the LABOCA Extended Chandra Deep Field South Sub-mm Survey ( LESS ) .
We select various classes of galaxies ( K -selected , star-forming sBzK galaxies , extremely red objects and distant red galaxies ) according to their optical/NIR fluxes .
We find clear , > 10 - \sigma detections in the stacked images of all these galaxy classes .
We include in our stacking analysis Herschel /SPIRE data to constrain the dust SED of these galaxies .
We find that their dust emission is well described by a modified black body with T _ { dust } \approx 30 K and \beta = 1.6 and IR luminosities of ( 5 - 11 ) \times 10 ^ { 11 } L _ { \odot } , or implied star formation rates of 75–140 M _ { \odot } yr ^ { -1 } .
We compare our results with those of previous studies based on single-dish observations at 870 \mu m and find that our flux densities are a factor 2–3 higher than previous estimates .
The discrepancy is observed also after removing sources individually detected in ALESS maps .
We report a similar discrepancy by repeating our analysis on 1.4 GHz observations of the whole ECDFS .
Hence we find tentative evidence that galaxies that are associated in projected and redshift space with sub-mm bright sources are brighter than the average population .
Finally , we put our findings in the context of the cosmic star formation rate density as a function of redshift .