=====================================================================
==> In this proposal, more time is being requested for TONAKA.IRGAL_1
==> This proposal requests an upgrade from Priority 3 for TONAKA.IRGAL_1
=====================================================================
The origin of the IR emission from normal galaxies and its relation to the
properties of galaxies is poorly understood.  There are known to be a
systematic variation in the MIR to FIR emission from galaxies and the IR
emission of galaxies is thought to consist of several components.  However, a
clear identification and origin of each component still remain open problems.
These properties and components can be studied in the framework of an analogue
to the diffuse IR emission in our Galaxy.  In the first call proposal,
TONAKA.IRGAL_1, we have proposed ISO observations to complement the IRTS/MIRS
observations and study the IR properties of external galaxies. The observations
made by the Mid-IR spectrometer (MIRS) on board the Infrared Telescope in Space
(IRTS) detected the Unidentified IR (UIR) bands in the diffuse galactic
emission.  They have also indicated that most MIR emission in the diffuse medium
comes from the UIR bands.  The FIR spectroscopy of external galaxies together
with the MIR imaging by ISO can thus elucidate the origin of the IR emission
from external galaxies, complemented by the detailed study of the diffuse
emission in our Galaxy by IRTS/MIRS.  In this proposal, we request to upgrade
the grade 3 observations of IRGAL_1 and to add three galaxies to cover a
sufficient range of the IR properties of galaxies. The results will lead to a
better understanding of the IR properties of external galaxies with the
complementary study by the IRTS/MIRS.