2018A&A...620A.152F

Aims. We present a 69 arcmin² ALMA survey at 1.1mm, GOODS-ALMA, matching the deepest HST-WFC3 H-band part of the GOODS-South field.
Methods. We tapered the 0.24" original image with a homogeneous and circular synthesized beam of 0.60" to reduce the number of independent beams - thus reducing the number of purely statistical spurious detections - and optimize the sensitivity to point sources. We extracted a catalog of galaxies purely selected by ALMA and identified sources with and without HST counterparts down to a 5σ limiting depth of H=28.2 AB (HST/WFC3 F160W).
Results. ALMA detects 20 sources brighter than 0.7mJy at 1.1mm in the 0.60" tapered mosaic (rms sensitivity σ~=0.18mJy/beam) with a purity greater than 80%. Among these detections, we identify three sources with no HST nor Spitzer-IRAC counterpart, consistent with the expected number of spurious galaxies from the analysis of the inverted image; their definitive status will require additional investigation. We detect additional three sources with HST counterparts either at high significance in the higher resolution map, or with different detection-algorithm parameters ensuring a purity greater than 80%. Hence we identify in total 20 robust detections.
Conclusions. Our wide contiguous survey allows us to push further in redshift the blind detection of massive galaxies with ALMA with a median redshift of z=2.92 and a median stellar mass of M*=1.1x10¹¹M_☉. Our sample includes 20% HST-dark galaxies (4 out of 20), all detected in the mid-infrared with Spitzer-IRAC. The near-infrared based photometric redshifts of two of them (z∼4.3 and 4.8) suggest that these sources have redshifts z>4. At least 40% of the ALMA sources host an X-ray AGN, compared to ∼14% for other galaxies of similar mass and redshift. The wide area of our ALMA survey provides lower values at the bright end of number counts than single-dish telescopes affected by confusion.