paper

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

arXiv:1607.02511 · doi:10.3847/0067-0049/226/2/19

Abstract

We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/PACS archive for a sample of 170 local AGN, 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 spectral range. The observations are compared to a set of CLOUDY photoionisation 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 ionisation potential of the emission lines. The new [OIV]25.9/[OIII]88 vs [NeIII]15.6/[NeII]12.8 diagram is proposed as the best diagnostic to separate: AGN activity from any kind of star formation; and low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [OIV]25.9/[OIII]88 ratios, which are much higher when compared to the predicted values. Finally, the ([NeIII]15.6 + [NeII]12.8)/([SIV]10.5 + [SIII]18.7) 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 (). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as JWST, ALMA, and SPICA.

arXiv commentAccepted for publication in the ApJS

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