GOODS-ALMA: 1.1 mm galaxy survey -I. Source catalogue and optically dark galaxies
GOODS-ALMA: 1.1 mm galaxy survey
Résumé
Aims. We present a 69 arcmin 2 ALMA survey at 1.1mm, GOODS–ALMA, matching the deepest HST–WFC3 H-band part of the GOODS–South field. Methods. We taper 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 extract a catalogue of galaxies purely selected by ALMA and identify sources with and without HST counterparts. Results. ALMA detects 20 sources brighter than 0.7 mJy at 1.1mm in the 0 60 tapered mosaic (rms sensitivity σ 0.18 mJy.beam −1) 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. An additional three sources with HST counterparts are detected 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 = 1.1 × 10 11 M. 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.
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