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Low gas-phase metallicities of ultraluminous infrared galaxies are a result of dust obscuration

Chartab, Nima and Cooray, Asantha and Ma, Jingzhe and Nayyeri, Hooshang and Zilliot, Preston and Lopez, Jonathan and Fadda, Dario and Herrera-Camus, Rodrigo and Malkan, Matthew and Rigopoulou, Dimitra and Sheth, Kartik and Wardlow, Julie (2022) Low gas-phase metallicities of ultraluminous infrared galaxies are a result of dust obscuration. Nature Astronomy, 6 (7). pp. 844-849. ISSN 2397-3366. doi:10.1038/s41550-022-01679-y.

[img] Image (JPEG) (Extended Data Fig. 1: Metal abundances of galaxies using the oxygen and nitrogen spectral emission lines) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 2: Metal abundances of galaxies depends on the assumptions related to oxygen and nitrogen ratios relative to hydrogen) - Supplemental Material
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[img] Image (JPEG) (Extended Data Fig. 3: Line maps and spectra of our sample targeted by SOFIA/FIFI-LS) - Supplemental Material
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Optical spectroscopic measurements show that gas in dusty, starbursting galaxies known as ultraluminous infrared galaxies (ULIRGs) in the local Universe has a significantly lower metal content than that of gas in star-forming galaxies with similar masses. This low metal content has resulted in the claim that ULIRGs are primarily fuelled by metal-poor gas falling into those galaxy merger systems from large distances. Here we report a new set of gas-phase metal abundance measurements taken in local ULIRGs using emission lines at far-infrared wavelengths tracing oxygen and nitrogen. These new data show that ULIRGs lie on the fundamental metallicity relation determined by the stellar mass, metal abundance and star formation rate as the key observational parameters. Instead of metal-poor gas accretion, the new data suggest that the underabundance of metals derived from optical emission lines is probably due to heavy dust obscuration associated with the starburst. As dust-obscured, infrared-bright galaxies dominate the star formation rate density of the Universe during the peak epoch of star formation, we caution the use of rest-frame optical measurements alone to study the metal abundances of galaxies at redshifts of 2–3.

Item Type:Article
Related URLs:
URLURL TypeDescription ReadCube access ItemNASA/IPAC Infrared Science Archive ItemSOFIA data reduction pipelines ItemSOSPEX
Chartab, Nima0000-0003-3691-937X
Cooray, Asantha0000-0002-3892-0190
Ma, Jingzhe0000-0003-4178-0800
Nayyeri, Hooshang0000-0001-8242-9983
Fadda, Dario0000-0002-3698-7076
Herrera-Camus, Rodrigo0000-0002-2775-0595
Malkan, Matthew0000-0001-6919-1237
Rigopoulou, Dimitra0000-0001-6854-7545
Sheth, Kartik0000-0002-5496-4118
Wardlow, Julie0000-0003-2376-8971
Additional Information:© The Author(s), under exclusive licence to Springer Nature Limited 2022. Received 12 January 2022; Accepted 11 April 2022; Published 26 May 2022. Results in this paper are based on observations made with the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract number NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR contract number 50-OK-0901 to the University of Stuttgart. Financial support for part of this work was also provided by NASA through award number 80NSS20K0437. J.W. acknowledges support from an STFC Ernest Rutherford Fellowship (ST/P004784/2). Data availability: Data supporting this study are publicly available or will be available by June 2022 through the NASA/IPAC Infrared Science Archive at under Plan ID 08-0095. SOFIA/FIFI-LS observations are publicly available for all the sources except for IRAS 12112+0305 and Mrk273 which will be made available by June 2022. Code availability: The SOFIA data reduction pipelines and SOSPEX are publicly available at and, respectively. All other code used in this work is available upon reasonable request. Contributions: N.C. and A.C. authored the draft version of this paper. N.C. measured line fluxes and FIR metallicities of the sample and conducted the analysis of this paper. A.C., J.M., H.N. and J.W. were PI/co-I in the successful SOFIA proposal and performed the observations. D.F. reduced the SOFIA/FIFI-LS data for the ULIRG sample used in this work. All other coauthors contributed extensively to interpreting the results of this paper and provided comments on this manuscript as part of an internal review process. The authors declare no competing interests. Peer review information: Nature Astronomy thanks Filippo Mannucci and Francois Hammer for their contribution to the peer review of this work.
Funding AgencyGrant Number
Deutsches Zentrum für Luft- und Raumfahrt (DLR)50-OK-0901
Science and Technology Facilities Council (STFC)ST/P004784/2
Subject Keywords:Galaxies and clusters; Interstellar medium
Issue or Number:7
Record Number:CaltechAUTHORS:20220531-100924600
Persistent URL:
Official Citation:Chartab, N., Cooray, A., Ma, J. et al. Low gas-phase metallicities of ultraluminous infrared galaxies are a result of dust obscuration. Nat Astron 6, 844–849 (2022).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114958
Deposited By: Tony Diaz
Deposited On:31 May 2022 16:04
Last Modified:02 Aug 2022 21:56

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