The following document lists the file abstract/DRIGOPOU_ULG_PAH.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
Observations we have obtained during the first half year of ISO have clearly demonstrated that ISO spectroscopy can provide key information to determine the nature of ultraluminous IRAS galaxies: 1) SWS spectroscopy of fine structure lines penetrates the high extinction and provides a quantitative diagnostic of the ionizing continuum (Starburst or AGN). This powerful technique is however limited to the brightest dozen of ULIRGs for sensitivity reasons; these observations form a key part of our guaranteed time observations. 2) Low resolution PHT-S spectra we have obtained on a small number of ULIRGS in guaranteed time (fig.1) clearly observe a significant spread in the absolute and relative strengths of PAH emission features. It is expected from pre-ISO data and confirmed by ISO spectroscopy that the behaviour of the PAH features reflects the strength and properties of the radiation field in which they are excited and may distinguish between AGNs and starbursts. Observations of PAH features thus provide a second route to obtain quantitative information on the nature of luminous IRAS galaxies, having less direct diagnostic power but allowing to observe a larger and complete sample allowing detailed statistical analysis. We hence propose to carry out a survey of low resolution 2.5-12um spectroscopy of emission features in a complete sample of ultraluminous IRAS galaxies. We point out that ISO will provide a wide database of comparison objects of various types (Seyferts, Starbursts, normal galaxies, galactic sources...), both from our own observations and those of a variety of other groups.