Spectral Energy Distributions of Companion Galaxies to z ∼ 6 Quasars

Creators: Mazzucchelli, C.; Decarli, R.; Farina, E. P.; Bañados, E.; Venemans, B. P.; Strauss, M. A.; Walter, F.; Neeleman, M.; Bertoldi, F.; Fan, X.; Riechers, D.; Rix, H.-W.; Wang, R.

Abstract

Massive, quiescent galaxies are already observed at redshift z ~ 4, i.e., ~1.5 Gyr after the big bang. Current models predict them to be formed via massive, gas-rich mergers at z > 6. Recent ALMA observations of the cool gas and dust in z ≳ 6 quasars have discovered [C II]- and far-infrared-bright galaxies adjacent to several quasars. In this work, we present sensitive imaging and spectroscopic follow-up observations, with HST/WFC3, Spitzer/IRAC, VLT/MUSE, Magellan/FIRE, and LBT/LUCI-MODS, of ALMA-detected, dust-rich companion galaxies of four quasars at z ≳ 6, specifically acquired to probe their stellar content and unobscured star formation rate. Three companion galaxies do not show significant emission in the observed optical/IR wavelength range. The photometric limits suggest that these galaxies are highly dust-enshrouded, with unobscured star formation rates SFR_(UV) < few M⊙ yr^(−1), and a stellar content of M* < 10^(10) M⊙ yr^(−1). However, the companion to PJ167−13 shows bright rest-frame UV emission (F140W AB = 25.48). Its spectral energy distribution resembles that of a star-forming galaxy with a total SFR ~ 50 M⊙ yr^(−1) and M* ~ 9 × 10^9 M⊙. All the companion sources are consistent with residing on the galaxy main sequence at z ~ 6. Additional, deeper data from future facilities, such as the James Webb Space Telescope, are needed in order to characterize these gas-rich sources in the first gigayear of cosmic history.

Additional Information

© 2019 The American Astronomical Society. Received 2019 February 4; revised 2019 July 2; accepted 2019 July 3; published 2019 August. We are grateful to the anonymous referee for constructive feedback. We thank J. Heidt for the acquisition of the LBT/LUCI data. C.M. acknowledges G. Popping, A. Drake, N. Kacharov, and E. Da Cunha for useful insights on galaxy spectral modeling, and for support on the use of MAGPHYS. C.M. thanks I. Georgiev, K. Jahnke, and A. Merritt for precious advice on PSF modeling and subtraction. B.P.V. and F.W. acknowledge funding through the ERC grants "Cosmic Dawn" and "Cosmic Gas." D.R. acknowledges support from the National Science Foundation under grant No. AST-1614213. C.M. thanks the IMPRS for Astronomy and Cosmic Physics at the University of Heidelberg. The present work is based on observations taken with ESO Telescopes at the La Silla Paranal Observatory, under the programs: 099.A-0682, 297.A-5054. This paper includes data gathered with the 6.5 m Magellan Telescope located at Las Campanas Observatory, Chile. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia. This paper used data obtained with the MODS spectrographs built with funding from NSF grant AST-9987045 and the NSF Telescope System Instrumentation Program (TSIP), with additional funds from the Ohio Board of Regents and the Ohio State University Office of Research. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 14876. Support for this work was provided by NASA through grant No. 10747 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This work is based [in part] on observations made and archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration 2018; http://www.astropy.org). Facilities: VLT:Yepun (MUSE) - , Magellan:Baade (FIRE) - , LBT (MODS - , LUCI) - , ALMA - , HST (WFC3) - , Spitzer (IRAC). -

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