• Fernández-Ontiveros, Juan Antonio
;
• Spinoglio, Luigi
;
• Pereira-Santaella, Miguel
;
• Malkan, Matthew A.
;
• Andreani, Paola
;
• Dasyra, Kalliopi M.

Abstract

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]{}_{25.9μ {{m}}}/[O III]{}_{88μ {{m}}} versus [Ne III]{}_{15.6μ {{m}}}/[Ne II]{}_{12.8μ {{m}}} 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]{}_{25.9μ {{m}}}/[O III]{}_{88μ {{m}}} ratios, which are much higher when compared to the predicted values. Finally, the ([Ne III]{}_{15.6μ {{m}}} + [Ne II]{}_{12.8μ {{m}}})/([S IV]{}_{10.5μ {{m}}} +[S III]{}_{18.7μ {{m}}}) 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\lt z\lt 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.