until recently, elliptical galaxies were thought mostly as old systems having exhausted their interstellar medium (ism). iras changed that view: dust, as well as molecular gas, is now frequently detected. a second idea that was revised recently is that dust should be colder in ellipticals than in spirals because of the lack of star formation. this is not the case as the very high density of stars in the central parts of the ellipticals and the concentration of dust in these regions lead to a higher equilibrium temperature (sauvage & thuan 1994). but the origin of their 12 microns emission is still a matter of controversy: knapp et al. (1992) brought evidence for a circumstellar origin, while sauvage & thuan (1994) show that an interstellar origin would better explain the far-infrared properties. the proposed observations aim at resolving that controversy. we propose to make a short wavelength (7-13mic) spectroscopic survey of elliptical galaxies. this survey will allow us to: i - assess the relative importance of circumstellar radiation as compared to interstellar radiation, as the spectra will be markedly different in the 2 cases. ii - compare the spectral properties of dust in ellipticals and spirals, in view of the likely external origin of dust in ellipticals. iii - identify the heating sources. the mir-emitting dust is very sensitive to the shape of the heating spectrum. from its emission spectrum, we shall constrain the origin of the dust heating, i.e. residual star formation, hot evolved stars, or an active nucleus?
Instrument
CAM01 , CAM04
Temporal Coverage
1996-02-14T11:22:07Z/1998-01-28T02:28:30Z
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.
