  High-redshift clusters of galaxies are amongst the largest cosmic structures.
Their properties and evolution are key ingredients to our understanding of
cosmology: to study the growth of structure from the inhomogeneities of the
cosmic microwave background; the processes of galaxy formation, evolution, and
differentiation; and to measure the cosmological parameters (through their
interaction with the geometry of the universe, the age estimates of their
component galaxies, or the measurement of the amount of matter locked in their
potential wells). However, not much is yet known about the properties of
clusters at redshifts of cosmological interest. We propose here a radically new
method to study large samples of cluster galaxies using microslits to perform
spectroscopy of huge numbers of objects in single fields in a narrow spectral
range-chosen to fit an emission line at the cluster redshift. Our objective is
to obtain spectroscopy in a very restricted wavelength range (~100 A in width)
of several thousands of objects for each single 8x8 square arcmin field.
Approximately 100 of them will be identified as cluster emission-line objects
and will yield basic measurements of the dynamics and the star formation in the
cluster (that figure applies to a cluster at z~0.50, and becomes ~40 and ~20
for clusters at z~0.75 and z~1.00 respectively). This is a pioneering approach
that, once proven, will be followed in combination with photometric redshift
techniques and applied to other astrophysical problems.
