GOODS-ALMA: 1.1 mm galaxy survey

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.

The ALMA Spectroscopic Survey in the HUDF: A Model to Explain Observed 1.1 and 0.85 mm Dust Continuum Number Counts

“…Interestingly enough, the median redshift of the redshift distributions is very similar for all three survey depths (around z = 1.5, although note that the uncertain z < 1 redshift range at which our model may over predict the brightness of sources is included). This seems in tension with observational results (e.g., the higher median redshift of Franco et al (2018) than González-López et al (2020)), similar to what we saw in Figure 6. At 1.1 millimeter, a survey reaching a depth of 0.1 mJy will detect approximately an order of magnitude more sources at 1 < z < 4 (up to a factor of 30 at z ∼ 5) than a survey reaching a depth of 1 mJy.…”

“…The low-number statistics of detections at z > 4 makes it hard to further quantify the success of the presented model. Possibly most surprising is the lack of sources detected by Franco et al (2018) at z < 2 compared to our model predictions. We additionally find that at ∼ 1 mJy, our model predicts number counts higher than derived by Franco et al (2018).…”

“…Possibly most surprising is the lack of sources detected by Franco et al (2018) at z < 2 compared to our model predictions. We additionally find that at ∼ 1 mJy, our model predicts number counts higher than derived by Franco et al (2018). Given the success of our model in reproducing the number counts by González-López et al (2020), the apparent mismatch with Franco et al may suggest a tension between the model predictions and observations for the brightest millimeter sources, but we note that not all sources in the Franco et al 2018 sample have a spectroscopic redshift.…”

“…We additionally find that at ∼ 1 mJy, our model predicts number counts higher than derived by Franco et al (2018). Given the success of our model in reproducing the number counts by González-López et al (2020), the apparent mismatch with Franco et al may suggest a tension between the model predictions and observations for the brightest millimeter sources, but we note that not all sources in the Franco et al 2018 sample have a spectroscopic redshift. Furthermore, a prior based selection of the data presented in Franco et al suggested that additional sources may have been missed in the blind selection, which may change the redshfit distribution (Franco et al in prep).…”

“…For this compari-son, we adopt the same field-of-view and sensitivity cutoff as the observations. We compare our predictions to observational results by Franco et al (2018) and González-López et al (2020). These works probe the 1.1 millimeter number counts over an area of 69 arcmin 2 (Franco et al 2018) down to 0.874 mJy and an area of 4.2 arcmin 2 down to 0.034 mJy (González-López et al 2020).…”