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AKARI 2.5–5 micron spectra of luminous infrared galaxies in the local Universe

Inami, H. and Armus, L. and Matsuhara, H. and Charmandaris, V. and Díaz-Santos, T. and Surace, J. and Stierwalt, S. and Ohyama, Y. and Howell, J. and Marshall, J. and Evans, A. S. and Linden, S. T. and Mazzarella, J. (2018) AKARI 2.5–5 micron spectra of luminous infrared galaxies in the local Universe. Astronomy and Astrophysics, 617 . Art. No. A130. ISSN 0004-6361.

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We present AKARI 2.5–5 μm spectra of 145 local luminous infrared galaxies (LIRG; L_(IR) ≥ 10^(11) L⊙) in the Great Observatories All-sky LIRG Survey (GOALS). In all of the spectra, we measure the line fluxes and equivalent widths (EQWs) of the polycyclic aromatic hydrocarbon (PAH) at 3.3 μm and the hydrogen recombination line Brα at 4.05 μm, with apertures matched to the slit sizes of the Spitzer low-resolution spectrograph and with an aperture covering ∼95% of the total flux in the AKARI two-dimensional (2D) spectra. The star formation rates (SFRs) derived from the Brα emission measured in the latter aperture agree well with SFRs estimated from LIR, when the dust extinction correction is adopted based on the 9.7 μm silicate absorption feature. Together with the Spitzer Infrared Spectrograph (IRS) 5.2–38 μm spectra, we are able to compare the emission of the PAH features detected at 3.3 μm and 6.2 μm. These are the two most commonly used near/mid-infrared indicators of starburst or active galactic nucleus (AGN) dominated galaxies. We find that the 3.3 μm and 6.2 μm PAH EQWs do not follow a linear correlation and at least a third of the galaxies classified as AGN-dominated sources using the 3.3 μm feature are classified as starbursts based on the 6.2 μm feature. These galaxies have a bluer continuum slope than galaxies that are indicated to be starburst-dominated by both PAH features. The bluer continuum emission suggests that their continuum is dominated by stellar emission rather than hot dust. We also find that the median Spitzer/IRS spectra of these sources are remarkably similar to the pure starburst-dominated sources indicated by high PAH EQWs in both 3.3 μm and 6.2 μm. Based on these results, we propose a revised starburst/AGN diagnostic diagram using 2–5 μm data: the 3.3 μm PAH EQW and the continuum color, F_ν(4.3 μm)/F_ν(2.8 μm). We use the AKARI and Spitzer spectra to examine the performance of our new starburst/AGN diagnostics and to estimate 3.3 μm PAH fluxes using the James Webb Space Telescope (JWST) photometric bands in the redshift range 0 < z < 5. Of the known PAH features and mid-infrared high ionization emission lines used as starburst/AGN indicators, only the 3.3 μm PAH feature is observable with JWST at z > 3.5, because the rest of the features at longer wavelengths fall outside the JWST wavelength coverage.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Inami, H.0000-0003-4268-0393
Armus, L.0000-0003-3498-2973
Charmandaris, V.0000-0002-2688-1956
Díaz-Santos, T.0000-0003-0699-6083
Surace, J.0000-0001-7291-0087
Stierwalt, S.0000-0002-2596-8531
Evans, A. S.0000-0003-2638-1334
Linden, S. T.0000-0002-1000-6081
Mazzarella, J.0000-0002-8204-8619
Additional Information:© 2018 ESO. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received 19 March 2018; Accepted 11 June 2018; Published online 02 October 2018. The authors would like to thank the referee whose constructive comments helped to improve the manuscript. We would also like to thank the language editor Ruth Chester at A&A for helpful revisions of this manuscript. HI appreciate Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) Fellows (21-969) and JSPS Excellent Young Researchers Overseas Visit Program for supporting this work at the Spitzer Science Center, California Institute of Technology, USA. YO acknowledges support from Ministry of Science and Technology (MOST) of Taiwan 106-2112-M-001-008-. This research is based on observations with AKARI, a JAXA project with the participation of ESA. The authors appreciated the opportunity to present this work at the 4th AKARI international conference, which helped to enrich this work (Inami et al. 2018). The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. This research has made use of the NASA/IPAC Extragalactic Database (NED) and the Infrared Science Archive (IRSA), which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)21-969
Ministry of Science and Technology (Taipei)106-2112-M-001-008
Subject Keywords:galaxies: starburst – galaxies: active – infrared: galaxies
Record Number:CaltechAUTHORS:20181017-162439327
Persistent URL:
Official Citation:The AKARI 2.5–5 micron spectra of luminous infrared galaxies in the local Universe. H. Inami, L. Armus, H. Matsuhara, V. Charmandaris, T. Díaz-Santos, J. Surace, S. Stierwalt, Y. Ohyama, J. Howell, J. Marshall, A. S. Evans, S. T. Linden and J. Mazzarella. A&A, 617 (2018) A130. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90315
Deposited By: Tony Diaz
Deposited On:18 Oct 2018 16:39
Last Modified:18 Oct 2018 16:39

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