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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

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. (2018). GOODS-ALMA: 1.1 mm galaxy survey. Astronomy & Astrophysics 620: A152.

Author(s) from Durham


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.