Mid-Infrared properties of Early-type galaxies

Abstract

We have conducted a survey of early-type galaxies using the ISOCAMinstrument on board the Infrared Space Observatory (ISO)in order to probe their dustcontent. We present Mid-Infrared photometric properties for a sampleof 20 galaxies observed at 4.5, 7 and 15 μ$m. Using diagnosticcolor-color diagrams, we can delineate the different Mid-Infrared emissioncontribution from evolved stars, non-thermal emission from AGNs/radiosources, and dust.Detailed modelling of the Spectral Energy Distribution (SED)is performed showing that even though theemission from the evolved stellar population may account for a large part of the Mid-Infrared output, emission from the hot dust and the aromatic hydrocarbon bands (e.g. PAHs) is the main contributorin many cases. Modelling of the surface brightness distribution is alsomade, showing that most of the galaxies follow a de Vaucouleurs profile.The physical nature and spatial distribution of the dust that we findfrom our studies of early-type galaxies will help to constrainthe origin of the dust in those galaxies.