Volume 617, September 2018
|Number of page(s)||27|
|Published online||02 October 2018|
The AKARI 2.5–5 micron spectra of luminous infrared galaxies in the local Universe⋆
Univ. Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon (CRAL) UMR5574, 69230 Saint-Genis-Laval, France
2 Infrared Processing and Analysis Center, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
3 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Japan
4 Institute for Astronomy, Astrophysics, Space Applications & Remote Sensing, National Observatory of Athens, 15236 Penteli, Greece
5 University of Crete, Department of Physics, 71003 Heraklion, Greece
6 Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
7 Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville, VA 22904, USA
8 National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA
9 Academia Sinica, Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, National Taiwan University, No.1, Sec. 4 Roosevelt Rd., 10617 Taipei, Taiwan
10 Glendale Community College, 1500 North Verdugo Road, Glendale, CA 91208, USA
Accepted: 11 June 2018
We present AKARI 2.5–5 μm spectra of 145 local luminous infrared galaxies (LIRG; LIR ≥ 1011 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, Fν(4.3 μm)/Fν(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.
Key words: galaxies: starburst / galaxies: active / infrared: galaxies
Full Table 1 and data associated to Fig. 9 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/617/A130
© ESO 2018
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