Almacal I: First Dual-Band Number Counts From a Deep and Wide Alma Submillimeter Survey, Free From Cosmic Variance

Abstract

We have exploited ALMA calibration observations to carry out a novel, wide, and deep submillimeter (submm) survey, ALMACAL. These calibration data comprise a large number of observations of calibrator fields in a variety of frequency bands and array configurations. By gathering together data acquired during multiple visits to many ALMA calibrators, it is possible to reach noise levels which allow the detection of faint, dusty, star-forming galaxies (DSFGs) over a significant area. In this paper, we outline our survey strategy and report the first results. We have analyzed data for 69 calibrators, reaching depths of ∼25 μJy beam −1 at sub-arcsec resolution. Adopting a conservative approach based on 5σ detections, we have found 8 and 11 DSFGs in ALMA bands 6 and 7, respectively, with flux densities S 1.2 mm 0.2 mJy. The faintest galaxies would have been missed by even the deepest Herschel surveys. Our cumulative number counts have been determined independently at 870 μm and 1.2 mm from a sparse sampling of the astronomical sky, and are thus relatively free of cosmic variance. The counts are lower than reported previously by a factor of at least 2×. Future analyses will yield large, secure samples of DSFGs with redshifts determined via the detection of submm spectral lines. Uniquely, our strategy then allows for morphological studies of very faint DSFGs-representative of more normal star-forming galaxies than conventional submm galaxies-in fields where self-calibration is feasible, yielding milliarcsecond spatial resolution.

SXDF–ALMA 2-arcmin2 deep survey: 1.1-mm number counts

“…These counts could be biased because of the possible clustering around the original targets. In figure 6, we plot ALMA number counts obtained in the Extended Chandra Deep Field South (ECDFS) by Karim et al (2013) (870 µm) and in the UKIRT InfraRed Deep Sky Surveys (UKIDSS) Ultra Deep Survey (UDS) field by Simpson et al (2015) (870 µm), and ALMA number counts derived from serendipitously-detected sources by Hatsukade et al (2013) (1.3 mm), Ono et al (2014) (1.2 mm), Carniani et al (2015) (1.1 mm), Fujimoto et al (2016) (1.2 mm), and Oteo et al (2015) (1.2 mm). We also show the number counts obtained by single-dish surveys with MaxPlanck millimeter bolometer (MAMBO) at 1.2 mm (Lindner et al 2011) and AzTEC at 1.1 mm (Scott et al 2012) for the bright end.…”

“…In addition to the counts for ≥4σ sources, the cumulative counts for ≥5σ sources (blue squares) are also presented. For comparison, we plot ALMA number counts in the ECDFS (Karim et al 2013) and the UKIDSS UDS field (Simpson et al 2015), and counts derived from ALMA-detected serendipitous sources by Hatsukade et al (2013), Ono et al (2014), Carniani et al (2015), Fujimoto et al (2016), andOteo et al (2015). Number counts derived with single-dish surveys with MAMBO (Lindner et al 2011) (Lockman Hole North field) and AzTEC (Scott et al 2012) (combined counts of 6 blank fields) are also presented.…”

“…Recently Oteo et al (2015) present the number counts by using ≥5σ sources detected in the ALMA archival data of calibrators. Their counts are lower than previous results by a factor …”

THE SXDF-ALMA 2 arcmin2 DEEP SURVEY: STACKING REST-FRAME NEAR-INFRARED SELECTED OBJECTS

“…All magnitudes are given in the AB system, where m AB = 8.9−2.5 log(F) when flux F is in unit of Jansky. When we compare our 1.1 mm results with previous 1.3 mm and 870 µm results, we assume F 1.1 mm = 1.65 × F 1.3 mm (F16) and F 1.1 mm = F 870 µm /2.5 (Oteo et al 2016). …”

“…Sources detected in these ALMA surveys typically account for ∼ 40% of the EBL (e.g., Hatsukade et al 2016, hereafter H16;D16) and the majority of the dusty galaxies remain undetected. One way to break through the current sensitivity limit is, instead of relying on contiguous ALMA mosaic survey, to exploit the archived data where the individual pointings are sufficiently deep and to look for serendipitously detected faint objects (Hatsukade et al 2013;Ono et al 2014;Carniani et al 2015;Fujimoto et al 2016, hereafter F16;Oteo et al 2016). Another way is to employ stacking analyses to obtain averaged mm/submm properties of high-redshift galaxies (e.g., Decarli et al 2014;Scoville et al 2014, D16).…”