| dc.description.abstract | We present here photometric redshift confirmation of the presence of large-scale structure around the z= 1.82 quasi-stellar object (QSO) RX J0941, which shows an overdensity of submillimetre (submm) sources. Radio imaging confirms the presence of the submm sources and pinpoints their likely optical near-infrared (NIR) counterparts. Four of the five submm sources present in this field (including the QSO) have counterparts with redshifts compatible with z= 1.82. We show that our photometric redshifts are robust against the use of different spectral templates. We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K-band luminosity obtaining log(M*/M⊙) ∼ 11.5 ± 0.2, slightly larger than the Schechter mass of present-day galaxies, and hence indicating that most of the stellar mass is already formed. We present optical-to-radio spectral energy distributions (SEDs) of the five Submillimetre Common-User Bolometer Array (SCUBA) sources. The emission of RX J0941 is dominated by reprocessed active galactic nucleus (AGN) emission in the observed mid-IR (MIR) range, while the starburst contribution completely dominates in the submm range. The SEDs of the other three counterparts are compatible with a dominant starburst contribution above ∼24 μm, with star formation rates ∼2000 M⊙ yr−1, central dust masses log(Mdust/M⊙) ∼ 9 ± 0.5 and hence central gas masses log(Mgas/M⊙) ∼ 10.7. There is very little room for an AGN contribution. From X-ray upper limits and the observed 24 μm flux, we derive a maximum 2–10 keV X-ray luminosity of 1044 erg s−1 for any putative AGN, even if they are heavily obscured. This in turn points to relatively small black holes with log(M•/M⊙) ≲ 8 and hence stellar-to-black hole mass ratios about 1 order of magnitude higher than those observed in the present Universe: most of their central black hole masses are still to be accreted. Local stellar-to-black hole mass ratios can be reached if ∼1.3 per cent of the available nuclear gas mass is accreted. | es_ES |
| dc.description.sponsorship | The authors thank the anonymous referee for helpful suggestions to clarify the paper. FJC thanks M. Rowan-Robinson for his help with the SWIRE templates, R. Pelló for her help with HYPERZ and N. Benítez for his help with BPZ. FJC, JE and SF acknowledge financial support from the Spanish Ministerio de Educación y Ciencia (later Ministerio de Ciencia e Innovación) under projects ESP2006-13608-C02-01 and AYA2009-08059. FJC, JAS and MJP acknowledge further support from the Royal Society. Based on observations made at the William Herschel Telescope and at the Isaac Newton Telescope which is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Also based on observations obtained at the Gemini Observatory (under programme GN2004A-Q-52), 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 National Science Foundation (United States); the Science and Technology Facilities Council (United Kingdom); the National Research Council (Canada); CONICYT (Chile); the Australian Research Council (Australia); Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). UKIRT is operated by the Joint Astronomy Centre, Hilo, Hawaii on behalf of the UK Science and Technology Facilities Council. Also based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under National Aeronautics and Space Administration (NASA) contract 1407. The James Clerk Maxwell Telescope (JCMT) is operated by The Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the United Kingdom, the Netherlands Organization for Scientific Research and the National Research Council of Canada. JCMT data were taken under project ID M03AU46. Also based on data collected at the XMM–Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This research has made use of data obtained from the SuperCOSMOS Science Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. The NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities. We thank the staff of the GMRT who have made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. This publication makes use of data products from the 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the NASA and the NSF. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the NSF, the US Department of Energy, the NASA, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory and the University of Washington. | |
