We present an analysis of a deep ( 1 \sigma =13 \mu Jy ) cosmological 1.2-mm continuum map based on ASPECS , the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field .
In the 1 arcmin ^ { 2 } covered by ASPECS we detect nine sources at > 3.5 \sigma significance at 1.2-mm .
Our ALMA–selected sample has a median redshift of z = 1.6 \pm 0.4 , with only one galaxy detected at z > 2 within the survey area .
This value is significantly lower than that found in millimeter samples selected at a higher flux density cut-off and similar frequencies .
Most galaxies have specific star formation rates similar to that of main sequence galaxies at the same epoch , and we find median values of stellar mass and star formation rates of 4.0 \times 10 ^ { 10 } M _ { \sun } and \sim 40 ~ { } M _ { \sun } yr ^ { -1 } , respectively .
Using the dust emission as a tracer for the ISM mass , we derive depletion times that are typically longer than 300 Myr , and we find molecular gas fractions ranging from \sim 0.1 to 1.0 .
As noted by previous studies , these values are lower than using CO–based ISM estimates by a factor \sim 2 .
The 1 mm number counts ( corrected for fidelity and completeness ) are in agreement with previous studies that were typically restricted to brighter sources .
With our individual detections only , we recover 55 \pm 4 \% of the extragalactic background light ( EBL ) at 1.2 mm measured by the Planck satellite , and we recover 80 \pm 7 \% of this EBL if we include the bright end of the number counts and additional detections from stacking .
The stacked contribution is dominated by galaxies at z \sim 1 - 2 , with stellar masses of ( 1–3 ) \times 10 ^ { 10 } M _ { \odot } .
For the first time , we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm .