we have constructed from the iras database,a sample of data reaching a limiting 60microns flux of about 100mjy in a few regions of the sky, and covering about 100 square degrees both in the northern and in the southern hemisphere.this should allow to study the reliability of iras detections,the nature of the faintest iras sources and the number counts down to this faint flux with a reasonable sky coverage.while the number- counts reveal an excess above model-predictions (with and without evolution)for galaxies,but at a much lower flux then previously found, thus questioning the effective amplitude of the effect,the colours and fluxes indicate that the excess cannot be due to the already known populations of galaxies,including the blue dwarfs at z=0.5. on the other hand,the follow-up work to find the optical counterparts shows an increasing number of cases at faint flux level where more then one galaxy could contribute to the iras flux.the signification of the number-counts can therefore not be assessed before one has an estimate of the fraction of multiple-objects entering the counts.furthermore, we need to know whether at these flux levels,we see the same population of super-starbursters further out,or whether one starts to see a contribution from closeby but fainter ir-emitters. we therefore ask, for a representative subsample of sources,for cam imaging in the 12mu band to separate the various contributors in the far ir,together with two additional cam and one phot point to establish the spectral energy distribution of the sources. complementary ground-based photometry and spectroscopy is under way for a larger sample,in order to establish the nature of the extragalactic sources seen at the limit of sensitivity by iras.
Instrument
CAM01 , PHT04
Temporal Coverage
1996-08-07T04:44:17Z/1997-12-06T14:12:10Z
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 Nature Of The Faintest Iras Galaxies And Galaxy Evolution Follow-Up Of Iras \D_Commadeep-Field\D_Comma Sources, 1.0, European Space Agency, https://doi.org/10.5270/esa-a4uray0
