Far-infrared line spectra of active galaxies from the Herschel/PACS spectrometer: The complete database

Journal article

We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/Photoconductor Array Camera and Spectrometer archive for a sample of 170 local active galactic nuclei (AGNs), plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies. Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our database to the full 10-600 μm spectral range. The observations are compared to a set of Cloudy photoionization models to estimate the above physical quantities through different diagnostic diagrams. We confirm the presence of a stratification of gas density in the emission regions of the galaxies, which increases with the ionization potential of the emission lines. The new [O iv] 25.9μm /[O iii] 88μm versus [Ne iii] 15.6μm /[Ne ii] 12.8μm diagram is proposed as the best diagnostic to separate (1) AGN activity from any kind of star formation and (2) low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [O iv] 25.9μm /[O iii] 88μm ratios, which are much higher when compared to the predicted values. Finally, the ([Ne iii] 15.6μm + [Ne ii] 12.8μm )/([S iv] 10.5μm +[S iii] 18.7μm ) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity. The diagnostic power of mid- to far-infrared spectroscopy shown here for local galaxies will be of crucial importance to study galaxy evolution during the dust-obscured phase at the peak of the star formation and black hole accretion activity (1 < z < 4). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as the James Webb Space Telescope, the Atacama Large Millimeter/submillimeter Array, and the Space Infrared telescope for Cosmology and Astrophysics.

Authors: Fernández-Ontiveros, J; Spinoglio, L; Pereira-Santaella, M; Malkan, M; Andreani, P

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Institute of Physics
• Journal: Astrophysical Journal Supplement Series
• Volume: 226
• Issue: 2
• Pages: 19
• Publication date: 2016-10-01
• Acceptance date: 2016-07-06
• DOI: 10.3847/0067-0049/226/2/19
• EISSN: 1538-4365
• ISSN: 0067-0049
• Keywords: galaxies: nuclei; galaxies: dwarf; galaxies: Seyfert; galaxies: active; galaxies: starburst; galaxies: ISM