GOODS-ALMA: 1.1 mm galaxy survey. I. Source catalog and optically dark galaxies

December 2018 • 2018A&A...620A.152F

Authors • Franco, M. • Elbaz, D. • Béthermin, M. • Magnelli, B. • Schreiber, C. • Ciesla, L. • Dickinson, M. • Nagar, N. • Silverman, J. • Daddi, E. • Alexander, D. M. • Wang, T. • Pannella, M. • Le Floc'h, E. • Pope, A. • Giavalisco, M. • Maury, A. J. • Bournaud, F. • Chary, R. • Demarco, R. • Ferguson, H. • Finkelstein, S. L. • Inami, H. • Iono, D. • Juneau, S. • Lagache, G. • Leiton, R. • Lin, L. • Magdis, G. • Messias, H. • Motohara, K. • Mullaney, J. • Okumura, K. • Papovich, C. • Pforr, J. • Rujopakarn, W. • Sargent, M. • Shu, X. • Zhou, L.

Abstract •
Aims: We present a 69 arcmin² ALMA survey at 1.1 mm, 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 0.7 mJy at 1.1 mm 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. 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_⋆ = 1.1 × 10¹¹ 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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Ranga-Ram Chary

Senior Scientist