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The Interstellar Medium in High-redshift Submillimeter Galaxies as Probed by Infrared Spectroscopy

Wardlow, Julie L. and Cooray, Asantha and Osage, Willow and Bourne, Nathan and Clements, David L. and Dannerbauer, Helmut and Dunne, Loretta and Dye, Simon and Eales, Steve and Farrah, Duncan and Furlanetto, Cristina and Ibar, Edo and Ivison, Rob and Maddox, Steve and Michałowski, Michał J. and Riechers, Dominik and Rigopoulou, Dimitra and Scott, Douglas and Smith, Matthew W. L. and Wang, Lingyu and van der Werf, Paul and Valiante, Elisabetta and Valtchanov, Ivan and Verma, Aprajita (2017) The Interstellar Medium in High-redshift Submillimeter Galaxies as Probed by Infrared Spectroscopy. Astrophysical Journal, 837 (1). Art. No. 12. ISSN 1538-4357.

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Submillimeter galaxies (SMGs) at z ≿ 1 are luminous in the far-infrared, and have star formation rates, SFR, of hundreds to thousands of solar masses per year. However, it is unclear whether they are true analogs of local ULIRGs or whether the mode of their star formation is more similar to that in local disk galaxies. We target these questions by using Herschel-PACS to examine the conditions in the interstellar medium (ISM) in far-infrared luminous SMGs at z ~ 1–4. We present 70–160 μm photometry and spectroscopy of the [O IV]26 μm, [Fe II]26 μm, [S III]33 μm, [Si II]34 μm, [O III]52 μm, [N III]57 μm, and [O I]63 μm fine-structure lines and the S(0) and S(1) hydrogen rotational lines in 13 lensed SMGs identified by their brightness in early Herschel data. Most of the 13 targets are not individually spectroscopically detected; we instead focus on stacking these spectra with observations of an additional 32 SMGs from the Herschel archive—representing a complete compilation of PACS spectroscopy of SMGs. We detect [O I]63 μm, [Si II]34 μm, and [N III]57 μm at ≥ 3σ in the stacked spectra, determining that the average strengths of these lines relative to the far-IR continuum are (0.36 ± 0.12) x 10^(-3), (0.84 ± 0.17) x 10^(-3), and (0.27 ± 0.10) x 10^(-3), respectively. Using the [O III]52 μm/[N III]57 μm emission line ratio, we show that SMGs have average gas-phase metallicities ≿z_⊙. By using PDR modeling and combining the new spectral measurements with integrated far-infrared fluxes and existing [C II]158 μm data, we show that SMGs have average gas densities, n, of ~10^(1-3) cm^(-3) and FUV field strengths, G_0 ~ 10^(2.2-4.5) (in Habing units: 1.6 x 10^(-3) erg cm^(-2) s^(-1)), consistent with both local ULIRGs and lower luminosity star-forming galaxies.

Item Type:Article
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URLURL TypeDescription Paper
Wardlow, Julie L.0000-0003-2376-8971
Cooray, Asantha0000-0002-3892-0190
Clements, David L.0000-0002-9548-5033
Farrah, Duncan0000-0003-1748-2010
Riechers, Dominik0000-0001-9585-1462
van der Werf, Paul0000-0001-5434-5942
Valtchanov, Ivan0000-0001-9930-7886
Additional Information:© 2017 The American Astronomical Society. Received 2016 September 20; accepted 2017 January 9; published 2017 February 27. The authors thank Lee Armus, Jeronimo Bernard-Salas, Kristen Coppin, Tanio Díaz-Santos, Jonatan Selsing, Ian Smail, Mark Swinbank, and Zhi-Yu Zhang for helpful discussions, and an anonymous referee for constructive and clarifying comments. We are grateful to Javier Graciá-Carpio, Eckhard Sturm, and the SHINING collaboration for providing a compilation of spectral observations and IR emission measurements used for comparison with our sample, and to Lucia Marchetti, Steve Crawford, Stephen Serjeant, and Andrew Baker for discussion regarding a followup South African Large Telescope program targeting lens redshifts (L. Marchetti et al. 2017, in preparation). J.L.W. is supported by a European Union COFUND/Durham Junior Research Fellowship under EU grant agreement number 267209, and acknowledges additional support from STFC (ST/L00075X/1). Support for this work was provided by NASA through an award issued by JPL/Caltech. A.C. and J.L.W. acknowledge support from NSF AST-1313319 and NASA NNX16AF38G. H.D. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under the 2014 Ramón y Cajal program MINECO RYC-2014-15686. L.D., S.J.M. and R.J.I. acknowledge support from European Research Council Advanced Investigator Grant COSMICISM, 321302; S.J.M. and L.D. are also supported by the European Research Council Consolidator Grant CosmicDust (ERC-2014-CoG-647939, PI: H.L. Gomez). A.V. acknowledges support from the Leverhulme Trust through a Research Fellowship. The Dark Cosmology Centre is funded by the Danish National Research Foundation. J.L.W., A.C., H.D., and D.R. thank the Aspen Center for Physics for hospitality. This work is supported in part by the NSF under Grant Numbers PHY-1066293 and AST-1055919. This research was supported by the Munich Institute for Astro- and Particle Physics (MIAPP) of the DFG cluster of excellence "Origin and Structure of the Universe." This research has made use of data from the HerMES project ( HerMES is a Herschel Key Programme utilizing Guaranteed Time from the SPIRE instrument team, ESAC scientists, and a mission scientist. The data presented in this paper will be released through the HerMES Database in Marseille, HeDaM ( The Herschel-ATLAS ( is a project with Herschel, which is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia, with important participation from NASA. SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including: Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, and Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); and IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). HCSS/HSpot/HIPE are joint developments of the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. This research has made use of NASA's Astrophysics Data System. Facilities: Herschel (PACS), Herschel (SPIRE).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
COFUND/Durham Junior Research Fellowship267209
Science and Technology Facilities Council (STFC)ST/L00075X/1
Ministerio de Economía, Industria y Competitividad (MINECO)RYC-2014-15686
European Research Council (ERC)321302
European Research Council (ERC)ERC-2014-CoG-647939
Leverhulme TrustUNSPECIFIED
Danish National Research FoundationUNSPECIFIED
Munich Institute for Astro- and Particle Physics (MIAPP)UNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
Subject Keywords:Galaxies: High-redshift; Galaxies: ISM; Galaxies: Star Formation; Gravitational Lensing: Strong; Submillimeter: General
Record Number:CaltechAUTHORS:20170227-113311459
Persistent URL:
Official Citation:Julie L. Wardlow et al 2017 ApJ 837 12
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74549
Deposited By: Melissa Ray
Deposited On:27 Feb 2017 20:39
Last Modified:21 Oct 2017 00:00

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