we propose to observe the outer regions of 3 elliptical/s0 galaxies with optical/hi shells in the fir with isophot in order find evidence for the presence of cool dust in the shells. a large fraction of elliptical and early type galaxies exhibit shells, possibly caused by interactions/merging with gas rich companions. we have found hi associated with the faint optical shells in 4 systems, the most prominent examples being centaurus a and ngc 2865. the kinematics of the hi cast doubt on several of the existing scenarios involving both internal and external origins for the outer shells. the external scenarios appear to have the most promise at the moment. the external scenarios describe infall of a companion object into the parent galaxy. this could be either a gas rich companion galaxy or primordial gas clouds. a way to discriminate between these possibilities is to search for the presence of dust in these outer regions where we found the hi. pointed observations with isophot at 135 and 200 micron will go a factor 10 deeper than the existing iras data where these shells have not been detected at a level of about 1 mjy/ster. these observations will not only provide clues about the presence of dust, but in the case of detection of emission also provide a measure of the fir energy distribution and hence the temperature of the dust, which we expect to be low.
Instrument
PHT22
Temporal Coverage
1996-08-22T23:37:50Z/1996-12-30T00:34:46Z
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.
