An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: High resolution 870um source counts

Alexander Karim, Mark Swinbank, Jackie Hodge, Ian Smail, Fabian Walter, Andy Biggs, James Simpson, Alice Danielson, David Alexander, Frank Bertoldi, Carlos de Breuck, Scott Chapman, Kristen Coppin, Helmut Dannerbauer, Alastair Edge, Thomas Greve, Rob Ivison, Kirsten Knudsen, Karl Menten, Eva SchinnererJulie Wardlow, Axel Weiß, Paul van der Werf

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We report the first counts of faint submillimetre galaxies (SMG) in the 870-um band derived from arcsecond resolution observations with the Atacama Large Millimeter Array (ALMA). We have used ALMA to map a sample of 122 870-um-selected submillimetre sources drawn from the (0.5x0.5)deg^2 LABOCA Extended Chandra Deep Field South Submillimetre Survey (LESS). These ALMA maps have an average depth of sigma(870um)~0.4mJy, some ~3x deeper than the original LABOCA survey and critically the angular resolution is more than an order of magnitude higher, FWHM of ~1.5" compared to ~19" for the LABOCA discovery map. This combination of sensitivity and resolution allows us to precisely pin-point the SMGs contributing to the submillimetre sources from the LABOCA map, free from the effects of confusion. We show that our ALMA-derived SMG counts broadly agree with the submillimetre source counts from previous, lower-resolution single-dish surveys, demonstrating that the bulk of the submillimetre sources are not caused by blending of unresolved SMGs. The difficulty which well-constrained theoretical models have in reproducing the high-surface densities of SMGs, thus remains. However, our observations do show that all of the very brightest sources in the LESS sample, S(870um)>12mJy, comprise emission from multiple, fainter SMGs, each with 870-um fluxes of 1 galaxies with gas masses in excess of ~5x10^10 M_Sun is
Original languageEnglish
Pages (from-to)2-9
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date16 Apr 2013
Publication statusPublished - Jun 2013


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