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One of the most powerful ways of testing cosmological theories
is to determine the three-dimensional distribution of matter,
in other words, how galaxies of different types are clustered.
The gravitational forces that led to the formation of galaxies in the early
Universe arose both from ordinary matter, which we can detect with
our telescopes, and from dark matter, which we can't. By studying
the distribution of galaxies over the sky, we can calculate the
sizes of the forces that produced them.
Galaxy Clustering
To make an adequate map of galaxy clustering we plan to make
an ultradeep survey of 1200 square degrees to magnitude 27 in
the g band. There is no hope
of measuring redshifts of the faintest galaxies spectroscopically,
so we will perform the survey in four wavebands and use
the measured colors of the galaxies as a guide to their redshifts.
Gravitational Lensing
Another powerful method of studying dark matter is by using gravitational
lensing. Light is slightly bent when it passes through
a gravitational field, irrespective of whether the gravitational
field is caused by dark matter or regular matter. We can use this
effect to measure the total mass in a galaxy cluster. Although
gravitational lensing sometimes produces spectacular effects, it
most often shows itself in subtle distortions in the shapes of
galaxies. By looking for correlations among the profiles of large
numbers of neighboring galaxies it is possible to make three dimensional
maps of the distribution of dark matter in clusters.
Other Galaxy Research
Other extragalactic projects that can be performed by Pan-STARRS
include an ultradeep survey to probe the formation of elliptical
galaxies, studies of dwarf and low-surface-brightness galaxies,
and a program to identify far-infrared sources from future satellite
surveys.
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