Institute of Astronomy

IR Spectroscopic Tracers for Galaxy Evolution Studies: the Spitzer/Herschel database

SpeakerTalk DateTalk Series
Juan Fernandez Ontiveros (IAC Tenerife)1 December 2017Institute of Astronomy Galaxies Discussion Group


The rest-frame mid- to far-IR range contains a unique suite of spectral lines and dust features that allow us to determine the physical conditions in galaxies (e.g. density, ionisation, heavy element abundances) using tracers with a feeble response to both extinction and temperature.

In this study we present a spectroscopic database of mid- to far-IR fine-structure lines observed with Spitzer/IRS and Herschel/PACS for a sample of 170 local AGN, 20 starburst galaxies, and 43 dwarf galaxies. The observations are compared to a set of Cloudy photoionisation models to estimate the physical quantities through the different diagnostic diagrams. The new [OIV]25.9um/[OIII]88um vs [NeIII]15.6um/[NeII]12.8um diagram is proposed as new IR BPT diagnostic diagram, able 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 [OIV]25.9um/[OIII]88um ratios, which are much higher when compared to the predicted values. Finally, the ([NeIII]15.6um +[NeII]12.8um)/([SIV]10.5um + [SIII]18.7um) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity.


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