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Dust-enshrouded AGNs Can Dominate Host-galaxy-scale Cold Dust Emission

McKinney, Jed and Hayward, Christopher C. and Rosenthal, Lee J. and Martínez-Galarza, Juan Rafael and Pope, Alexandra and Sajina, Anna and Smith, Howard A. (2021) Dust-enshrouded AGNs Can Dominate Host-galaxy-scale Cold Dust Emission. Astrophysical Journal, 921 (1). Art. No. 55. ISSN 0004-637X. doi:10.3847/1538-4357/ac185f.

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It is widely assumed that long-wavelength infrared (IR) emission from cold dust (T ∼ 20–40 K) is a reliable tracer of star formation even in the presence of a bright active galactic nucleus (AGN). Based on radiative transfer (RT) models of clumpy AGN tori, hot dust emission from the torus contributes negligibly to the galaxy spectral energy distribution (SED) at λ ≳ 100 μm. However, these models do not include AGN heating of host-galaxy-scale diffuse dust, which may have far-IR (FIR) colors comparable to cold diffuse dust heated by stars. To quantify the contribution of AGN heating to host-galaxy-scale cold dust emission at λ ≳ 100 μm, we perform dust RT calculations on a simulated galaxy merger both including and excluding the bright AGN that it hosts. By differencing the SEDs yielded by RT calculations with and without AGNs that are otherwise identical, we quantify the FIR cold dust emission arising solely from reprocessed AGN photons. In extreme cases, AGN-heated host-galaxy-scale dust can increase galaxy-integrated FIR flux densities by factors of 2–4; star formation rates calculated from the FIR luminosity assuming no AGN contribution can overestimate the true value by comparable factors. Because the FIR colors of such systems are similar to those of purely star-forming galaxies and redder than torus models, broadband SED decomposition may be insufficient for disentangling the contributions of stars and heavily dust-enshrouded AGNs in the most IR-luminous galaxies. We demonstrate how kiloparsec-scale resolved observations can be used to identify deeply dust-enshrouded AGNs with cool FIR colors when spectroscopic and/or X-ray detection methods are unavailable.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
McKinney, Jed0000-0002-6149-8178
Hayward, Christopher C.0000-0003-4073-3236
Rosenthal, Lee J.0000-0001-8391-5182
Martínez-Galarza, Juan Rafael0000-0002-5069-0324
Pope, Alexandra0000-0001-8592-2706
Sajina, Anna0000-0002-1917-1200
Additional Information:© 2021. The American Astronomical Society. Received 2021 March 22; revised 2021 July 26; accepted 2021 July 26; published 2021 October 29. We thank the anonymous referee, M. Symeonidis, K. Phadke, and E. Daddi for insightful comments on the manuscript, which helped us significantly improve this work. The Flatiron Institute is supported by the Simons Foundation. H.A.S. and J.R.M.-G. acknowledge partial support from NASA grants NNX14AJ61G and NNX15AE56G and from SOFIA grant NNA17BF53C (08_0069). L.R. acknowledges the SAO REU program, funded by the National Science Foundation REU and Department of Defense ASSURE programs under NSF grant AST-1659473 and by the Smithsonian Institution. The simulations in this paper were performed on the Odyssey cluster supported by the FAS Research Computing Group at Harvard University. This research has made use of NASA's Astrophysics Data System.
Funding AgencyGrant Number
Flatiron InstituteUNSPECIFIED
Simons FoundationUNSPECIFIED
Smithsonian InstitutionUNSPECIFIED
Subject Keywords:Infrared galaxies; AGN host galaxies; Galaxy evolution; Hydrodynamical simulations; Radiative transfer simulations; Ultraluminous infrared galaxies
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Infrared galaxies (790); AGN host galaxies (2017); Galaxy evolution (594); Hydrodynamical simulations (767); Radiative transfer simulations (1967); Ultraluminous infrared galaxies (1735)
Record Number:CaltechAUTHORS:20211117-174147707
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111921
Deposited By: Tony Diaz
Deposited On:17 Nov 2021 23:01
Last Modified:17 Nov 2021 23:01

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