Contents of: VI/111/./abstract/HVOELK_VIRGO5.abs

The following document lists the file abstract/HVOELK_VIRGO5.abs from catalogue VI/111.
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SCIENTIFIC ABSTRACT
We propose to study a complete volume-limited unbiased sample of 118 spiral,
irregular and dwarf galaxies from the VIRGO cluster in the 40 - 220 micron
spectral range with ISOPHOT and LWS. For the ISOPHOT observations, The
completeness limit of Bt = 18 magnitude corresponds to the maximum (confusion
limited) depth the instrument can achieve, allowing a complete dynamic range
in star-formation activity to be measured. In parallel, wherever instrument
sensitivity permits, we propose a degree of spectro-photometric resolution which
by far exceeds that of IRAS, to provide a basis for distinguishing between dust
components of different temperatures and grain size distributions in the
galaxian interstellar media. These FIR observations will furthermore spatially
resolve the central region from the disk for the giant spirals with diameters
exceeding a few arcminutes. This should allow a distinction between FIR activity
in the centres and the disks for about half the galaxies in the sample.

Using LWS, we further propose to survey a subsample of 50 spiral galaxies from
the PHT sample with integrated blue magnitudes Bt < 14.5, for emission in the
[CII] 158 micron fine structure line. This will probe not only photodissociation
regions associated with massive star formation, but also the quiescent diffuse
HI component of the interstellar medium. The observation list appended below
addresses only the LWS observations, since the full observation list is too
large to fit into a single proposal. The ISOPHOT observations are addressed in
four separate related proposals designated VIRGO1, 2, 3 and 4.

OBSERVATION SUMMARY
The LWS observations addressed by this proposal (VIRGO sub-proposal "VIRGO5")
are implemented as follows. LWS will be used for pointed observations in the
grating mode. The line scanning AOT LWS02 will be used to achieve a spectral
scan about the appropriately redshifted wavelength of the 158 micron CII line.
The wavelength range of the scan will cover two grating resolution elements on
either side of the line with four spectral samples per resolution element. The
scans will be performed in the fast scanning mode to ensure optimal detection
of weak emission superimposed on a strong continuum. The survey will be complete
for all fifty targets down to a line flux of 3.10**(-17)Wm**(-2) with a
signal-to-noise ratio of three in the line detection. As far as possible, the
observations are grouped into concatenated chains so that groups of galaxies
falling within a 1.5 degree radius of some point (the initial pointing in the
concatenated sequence) are observed contiguously. This minimises the spacecraft
slewing overhead (so increasing the observing efficiency) and allows efficient
correlation of measurements of the diffuse IR background with sequential
groupings of galaxy observations. Occasionally, a concatenated sequence of
observations begins with a very short pointing at a sky position chosen only
because it establishes the centre position for the subsequent concatenated chain
in a way which facilitates the optimal use of concatenation.

Due to the design of the LWS instrument in which the 10 detectors spectrally
multiplex during a wavelength scan, our CII line scans will also generate 10
fragments of spectra right across the LWS wavelength range giving information
about the broader continuum spectrum of the targets. We request this data coming
from all LWS detectors.


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