Early Science with the Large Millimeter Telescope: Detection of Dust Emission in Multiple Images of a Normal Galaxy at z > 4 Lensed by a Frontier Fields Cluster

Creators: Pope, Alexandra; Chary, Ranga-Ram

Abstract

We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z > 4 and the strong lensing model (μ = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 10^(10) L_⊙ and an obscured star formation rate of 14.6 ± 4.5 M_⊙ yr^(−1). The unobscured star formation rate from the UV is only 4.1 ± 0.3 M_⊙ yr^(−1), which means the total star formation rate (18.7 ± 4.5 M_⊙ yr^(−1)) is dominated (75%–80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 10^9 M_⊙, MACS0717_Az9 is one of only a handful of z > 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe.

Additional Information

© 2017 American Astronomical Society. Received 2016 May 30. Accepted 2017 March 6. Published 2017 April 3. We thank the referee for constructive comments on this paper. This work would not have been possible without the long-term financial support from the Mexican Science and Technology Funding Agency, CONACYT during the construction and early operational phase of the Large Millimeter Telescope Alfonso Serrano, as well as support from the the US National Science Foundation (NSF) via the University Radio Observatory program, INAOE and the University of Massachusetts, Amherst. This work utilizes gravitational lensing models produced by PIs Bradac, Natarajan & Kneib (CATS), Merten & Zitrin, Sharon, and Williams, and the GLAFIC and Diego groups. This lens modeling was partially funded by the HST Frontier Fields program conducted by STScI. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555. The lens models were obtained from the Mikulski Archive for Space Telescopes (MAST). We also thank J. Diego for information on their lens model. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. A.P. acknowledges valuable discussions with Sandy Faber, George Rieke and Adi Zitrin. I.A. and D.R.G. acknowledge support from CONACYT grants CB-2011-01-1672 and CB-2011-01-167281, respectively. M.L. acknowledges CNRS and CNES for support. D.M. acknowledges the support of the NSF under Grant 1513473, and from HST-AR-14302, provided by NASA through a grant from STScI, which is operated by AURA, under NASA contract NAS5-26555. D.L.V. acknowledges support from the NASA Keck PI Data Awards, administered by the NASA Exoplanet Science Institute. K.E.W. gratefully acknowledge support by NASA through Hubble Fellowship grant #HF2-51368 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA. Facilities: LMT, HST, Spitzer.

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