we propose sws spectroscopy of selected lines in a complete sample of 56 ultraluminous infrared galaxies (lir>10e12 lsun) at z<0.35 in order to establish the nature of their primary energy sources. the discovery of such galaxies was one of the major results of the iras survey 10 years ago but their nature remains unclear and construction of large samples for further study has taken time.they are generally mergers containing the largest concentrations of molecular gas known but relatively few exhibit qso/seyfert1 type optical spectra although their luminosities are in the qso range. it has been suggested, therefore, both that they are mostly powered by extreme starbursts and by dust enshrouded agn.s. a statistically valid test is of the utmost importance in view of speculation that they may represent different phases of an evolutionary sequence from starbursts in gas rich merging spirals via the formation of dust enshrouded agn.s to visible qso.s following dispersal of their obscuring dust by sn or agn driven winds. as extinction to their nuclei could correspond to av.s of 100 -1000mag searches for dust enshrouded agn.s in the optical are of limited value.iso now offers the unique capability for detecting and discriminating between starbursts and agn via spectroscopy of the neii12.8um,neiii15.6 and nev14.3/24.3 lines which trace 20-60ev photons and, based on theoretical line ratio diagrams, are optimum for our purpose. their fluxes should also be comparable to hbeta but at wavelengths where the extinction in mags is a factor 500 lower. (siix3.95um will be intrinsically fainter and suffers higher extinction but can be observed simultaneously with the ne lines and is of specific interest due to its high ionization potential (303ev) and recent detection in agn. observations of the ne lines to the same s/n ratio in our complete flux limited sample should establish a measure of the relative importance of starburst and agn activity which is statistically valid for whole uig population.
Instrument
SWS02
Temporal Coverage
1996-05-08T07:30:58Z/1997-01-31T22:08:06Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, MOORWOOD et al., 1999, 'ENERGY SOURCE IN ULTRALUMINOUS INFRARED GALAXIES STARBURSTS OR OBSCURED AGN.S IN IRAS GALAXIES', 1.0, European Space Agency, https://doi.org/10.5270/esa-8nkknwm
