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Observational constraints on the physical nature of submillimetre source multiplicity: chance projections are common

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posted on 25.05.2018, 15:32 by Christopher C. Hayward, Scott C. Chapman, Charles C. Steidel, Anneya Golob, Caitlin M. Casey, Daniel J. B. Smith, Adi Zitrin, Andrew W. Blain, Malcolm N. Bremer, Chian-Chou Chen, Kristen E. K. Coppin, Duncan Farrah, Eduardo Ibar, Michał J. Michałowski, Marcin Sawicki, Douglas Scott, Paul Van der Werf, Giovanni G. Fazio, James E. Geach, Mark Gurwel, Glen Petitpas, David J. Wilner
Interferometric observations have demonstrated that a significant fraction of single-dish submillimetre (submm) sources are blends of multiple submm galaxies (SMGs), but the nature of this multiplicity, i.e. whether the galaxies are physically associated or chance projections, has not been determined. We performed spectroscopy of 11 SMGs in six multicomponent submm sources, obtaining spectroscopic redshifts for nine of them. For an additional two component SMGs, we detected continuum emission but no obvious features. We supplement our observed sources with four single-dish submm sources from the literature. This sample allows us to statistically constrain the physical nature of single-dish submm source multiplicity for the first time. In three (3/7, or 43+39 −33 per cent at 95 per cent confidence) of the single-dish sources for which the nature of the blending is unambiguous, the components for which spectroscopic redshifts are available are physically associated, whereas 4/7 (57+33 −39 per cent) have at least one unassociated component. When components whose spectra exhibit continuum but no features and for which the photometric redshift is significantly different from the spectroscopic redshift of the other component are also considered, 6/9 (67+26 −37 per cent) of the single-dish sources are comprised of at least one unassociated component SMG. The nature of the multiplicity of one single-dish source is ambiguous. We conclude that physically associated systems and chance projections both contribute to the multicomponent single-dish submm source population. This result contradicts the conventional wisdom that bright submm sources are solely a result of merger-induced starbursts, as blending of unassociated galaxies is also important.


The Flatiron Institute is supported by the Simons Foundation. Some of this work was supported by a National Aeronautics and Space Administration (NASA) Keck PI Data Award, administered by the NASA Exoplanet Science Institute. EI acknowledges partial support from Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) through grant no.  1171710. MJM acknowledges the support of the National Science Centre, Poland through POLONEZ grant 2015/19/P/ST9/04010. This project has received funding from the European Union's Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no.  665778. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Partially based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). This research has made use of the NASA/Infrared Processing and Analysis Center (IPAC) Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the Nati



Monthly Notices of the Royal Astronomical Society, 2018, 476 (2), pp. 2278-2287 (10)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Monthly Notices of the Royal Astronomical Society


Oxford University Press (OUP), Royal Astronomical Society





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