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ALMACAL I : first dual-band number counts from a deep and wide ALMA submillimeter survey, free from cosmic variance.

Oteo, I. and Zwaan, M.A. and Ivison, R.J. and Smail, I. and Biggs, A.D. (2016) 'ALMACAL I : first dual-band number counts from a deep and wide ALMA submillimeter survey, free from cosmic variance.', Astrophysical journal., 822 (1). p. 36.

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.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.3847/0004-637X/822/1/36
Publisher statement:© 2016. The American Astronomical Society. All rights reserved.
Date accepted:17 February 2016
Date deposited:22 June 2016
Date of first online publication:02 May 2016
Date first made open access:22 June 2016

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