since their discovery by the iras satellite, the nature of ultraluminous iras galaxies (ulirgs) has been a subject of controversy. these objects have luminosities typical of quasars, with the vast majority (up to 99%) emitted in the far-ir. there is evidence for massive bursts of star formation in them, but it is unclear whether this, or a dust obscured active nucleus is responsible for their extreme luminosity. it has been suggested that they represent an early stage in the evolution of quasars, during which the nucleus is obscured by a large mass of dust which is only later expelled or destroyed, allowing the quasar to be seen. in this proposal we will observe the 10 most luminous ulirgs found in the oxford ulirg survey. these objects cover the whole gamut of ulirg optical spectral types whilst their luminosities are all > 10^12.8 solar. they are the subject of extensive ground-based followup observations. isophot observations of their mid- to far-ir spectral energy distributions (seds) will provide a unique insight into the energy generation processes at their core, since it allows us to see through much of the obscuring material. if ulirgs are powerwed by agns, we would expect to see evidence of the hot dust in an obscuring torus. iras data on these objects is not sufficiently complete, or high enough signal-to-noise to permit this analysis. if signs of a central engine are not seen, the alternative hypothesis, that ulirgs are powered by a massive starburst, will have to be considered. comparison of iso seds for ulirgs with more normal, lower luminosity starburst galaxies tests this idea. dust temperature, mass and opacity will also be determined with these observations, providing a complete picture of these objects. iso.s long wavelength capabilities make it uniquely powerful for observing ulirgs. with these observations we can finally understand what triggers such high luminosity activity in the far-ir.
Instrument
PHT03 , PHT22
Temporal Coverage
1996-10-29T14:05:29Z/1998-01-28T03:18:16Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the world's 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, 1999, The Spectral Energy Distribution Of Extreme Ultraluminous Iras Galaxies, 1.0, European Space Agency, https://doi.org/10.5270/esa-78xz4qn
